- Research Associate Professor, Physiology
- Research Associate Professor, Ophthalmology
Since August 1983 I had an uninterrupted career in different teaching and research positions with 5 different Universities in Asia, Europe and America. I published more than 40 peer reviewed articles in different reputed journals and contributed significantly to the field of ocular Physiology and Pharmacology.
I graduated with Doctor of Veterinary Medicine (DVM) degree in 1982 from Bangladesh Agricultural University. I was awarded University Prize for securing First position in the First Class and appointed as a Lecturer in the Department of Physiology and Pharmacology in the following year. During the tenure of my lectureship position I completed MSc in Pharmacology degree in 1985, again with distinction and secured First Class. I was promoted to Assistant professor in 1987 and worked in that position until Sept. 1990.
In 1990 I was awarded Commonwealth Scholarship by the Association of Universities in the United Kingdom to do my PhD in Pharmacology. Strictly speaking this was the start of my research career. I completed PhD in 1994 from the University of Glasgow, UK and because of my outstanding contribution in research I was immediately offered Postdoc position and worked for this University until 2001. During this period I had an outstanding achievement in establishing an experimental model, the perfused intact eye system to study ocular drugs. I published a number of manuscripts utilizing this model system with significant contribution to the field.
In 2001 I was invited by the School of Optometry of the Hong Kong Polytechnic University to help them establish an Ocular Pharmacology laboratory and appointed me as a Research Fellow and Visiting Lecturer. I worked there until June 2005. During this period I was able to adapt the intact eye preparation to record multifocal ERG and this was the first in vitro ERG record in the world. In this position I taught Pharmacology and Physiology to the optometry students.
In June 2005 I moved to the United States of America and since then I have been working as Assistant Professor including my present position at the University of Arizona. During this time I established a second model system, the primary culture of nonpigmented ciliary epithelial cells. I published a large number of peer reviewed papers in many reputed journals with significant contribution to ocular physiology and pharmacology research.
- Ph.D. Pharmacology
- University of Glasgow, Glasgow, United Kingdom
- Mechanisms of action of drugs used in the treatment of glaucoma.
- M.S. Pharmacology
- Bangladesh Agricultural University, Mymensingh, Bangladesh
- D.V.M. Veterinary Medicine
- Bangladesh Agricultural University, Mymensingh, Bangladesh
- University of Arizona, Tucson, Arizona (2006 - Ongoing)
- University of Louisville (2005 - 2006)
- Hong Kong Polytechnic University (2001 - 2005)
- University of Glasgow (1994 - 2001)
- Bangladesh Agricultural University (1987 - 1997)
- Bangladesh Agricultural University (1983 - 1987)
Licensure & Certification
- Certification of Registration as a Veterinary Practitioner., Bangladesh Veterynary Council (1986)
Systems Physiology, Ocular Physiology. Cellular and Molecular Physiology; General Pharmacology, Clinical Pharmacology.
Aqueous humor physiology and pharmacology, Lens transport physiology, Xenobiotics transport by the ocular ciliary epithelium.
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- Aw, M., Armstrong, T. M., Nawata, C. M., Bodine, S. N., Oh, J. J., Wei, G., Evans, K. K., Shahidullah, M., Rieg, T., & Pannabecker, T. L. (2018). Body mass-specific Na+, K+-ATPase activity in the medullary thick ascending limb - implications for species-dependent urine concentrating mechanisms. American journal of physiology. Regulatory, integrative and comparative physiology.More infoIn general, mammalian whole body mass-specific metabolic rate correlates positively with maximal urine concentration (Umax) irrespective of whether or not the species have adapted to arid or mesic habitat. Accordingly, we hypothesized that the thick ascending limb (TAL) of a rodent with markedly higher whole body mass-specific metabolism than rat exhibits a substantially higher TAL metabolic rate as estimated by Na+, K+-ATPase activity and Na+, K+-ATPase α1 gene and protein expression. The kangaroo rat inner stripe of the outer medulla exhibits significantly higher mean Na+, K+-ATPase activity (~70%) compared to 2 rat strains (Sprague-Dawley and Munich-Wistar), extending prior studies showing rat activity exceeds rabbit. Furthermore, higher expression of Na+, K+-ATPase α1 protein (~4-6-fold) and mRNA (~13-fold) and higher TAL mitochondrial volume density (~20%) occur in the kangaroo rat compared to both rat strains. Rat TAL Na+, K+-ATPase α1 protein expression is relatively unaffected by body hydration status or, shown previously, by dietary Na+, arguing against confounding effects from two unavoidably dissimilar diets: grain-based diet without water (kangaroo rat) or grain-based diet with water (rat). We conclude that higher Na+, K+-ATPase activity contributes to relationships between whole body mass-specific metabolic rate and high Umax. More vigorous TALNa+, K+-ATPase activity in kangaroo rat than rat may contribute to its steeper Na+ and urea axial concentration gradients, adding support to a revised model of the urine concentrating mechanism, which hypothesizes a leading role for vigorous active transport of NaCl, rather than countercurrent multiplication, in generating the outer medullary axial osmotic gradient.
- Mandal, A., Shahidullah, M., & Delamere, N. A. (2018). TRPV1-dependent ERK1/2 activation in porcine lens epithelium. Experimental eye research, 172, 128-136.More infoRecently we determined that the Transient Receptor Potential Vanilloid 4 ion channel (TRPV4) has a crucial signaling role in a pathway that regulates various aspects of lens epithelium function. Here, we report on a different TRPV channel, TRPV1, in porcine lens. The presence of TRPV1 in the lens was evident from RT-PCR studies and Western blot analysis of MAPK signaling pathway activation caused by the TRPV1 agonist capsaicin. TRPV1 mRNA was detected in the epithelium of porcine as well as human lens. Transient ERK1/2 and p38 MAPK phosphorylation was detected within 1 min in the epithelium isolated from intact porcine lenses exposed to capsaicin (100 nM), a selective TRPV1 agonist, and the response was significantly inhibited by A889245 (1.0 μM), a TRPV1 antagonist. A similar ERK 1/2 and p38 response in the epithelium, also inhibitable by A889245, was evident in lenses treated with hyperosmotic solution (350 vs 300 mOsm). Lenses pre-treated with either the cytosolic Ca chelator BAPTA-AM or the PKC inhibitor sotrastaurin (1.0 μM) had a diminished ERK1/2 activation response to capsaicin and hyperosmotic solution. Taken together the findings support the notion that TRPV1 functions as a plasma membrane ion channel that, when activated, permits the entry of extracellular calcium into the lens epithelium, leading to activation of PKC, ERK1/2 and p38 MAPK. It is significant that the findings confirm earlier proposals that hyperosmotic stress is linked to TRPV1 channel activation in the mouse lens. Further studies are ongoing to determine what functional changes are triggered by the TRPV1-linked signaling pathways and how they might relate to lens volume homeostasis.
- Matagne, V., Wondolowski, J., Frerking, M., Shahidullah, M., Delamere, N. A., Sandau, U. S., Budden, S., & Ojeda, S. R. (2018). Correcting deregulated Fxyd1 expression rescues deficits in neuronal arborization and potassium homeostasis in MeCP2 deficient male mice. Brain research, 1697, 45-52.More infoRett syndrome (RTT) is a neurodevelopmental disorder caused by mutations in the MECP2 gene. In the absence of MeCP2, expression of FXYD domain-containing transport regulator 1 (FXYD1) is deregulated in the frontal cortex (FC) of mice and humans. Because Fxyd1 is a membrane protein that controls cell excitability by modulating Na, K-ATPase activity (NKA), an excess of Fxyd1 may reduce NKA activity and contribute to the neuronal phenotype of Mecp2 deficient (KO) mice. To determine if Fxyd1 can rescue these RTT deficits, we studied the male progeny of Fxyd1 null males bred to heterozygous Mecp2 female mice. Maximal NKA enzymatic activity was not altered by the loss of MeCP2, but it increased in mice lacking one Fxyd1 allele, suggesting that NKA activity is under Fxyd1 inhibitory control. Deletion of one Fxyd1 allele also prevented the increased extracellular potassium (K) accumulation observed in cerebro-cortical neurons from Mecp2 KO animals in response to the NKA inhibitor ouabain, and rescued the loss of dendritic arborization observed in FC neurons of Mecp2 KO mice. These effects were gene-dose dependent, because the absence of Fxyd1 failed to rescue the MeCP2-dependent deficits, and mimicked the effect of MeCP2 deficiency in wild-type animals. These results indicate that excess of Fxyd1 in the absence of MeCP2 results in deregulation of endogenous K conductances functionally associated with NKA and leads to stunted neuronal growth.
- Shahidullah, M., Mandal, A., & Delamere, N. A. (2018). Activation of TRPV1 channels leads to stimulation of NKCC1 cotransport in the lens. American journal of physiology. Cell physiology.More infoLens ion homeostasis is crucial in maintaining water content and, in turn, refractive index and transparency of the multicellular syncytium-like structure. New information is emerging on the regulation of ion transport in the lens by mechanisms that rely on Transient Receptor Potential Vanilloid (TRPV) ion channels. We found recently that TRPV1 activation leads to Ca/PKC-dependent ERK1/2 signaling. Here we show that the TRPV1 agonist capsaicin (100 nM) and hyperosmotic solution (350 vs 300 mOsm) similarly cause an increase of bumetanide-inhibitable Rb uptake by intact porcine lenses and NKCC1 phosphorylation in the lens epithelium. The TRPV1 antagonist A889425 (1 µM) abolished the increases of Rb uptake and NKCC1 phosphorylation in response to hyperosmotic solution. Exposing lenses to hyperosmotic solution in the presence of MEK/ERK inhibitor U0126 (10 µM) or the WNK kinase inhibitor WNK463 (1 µM) also prevented NKCC1 phosphorylation and the Rb uptake responses to hyperosmotic solution. WNK463 did not prevent the increase in ERK1/2 phosphorylation that occurs in response to capsaicin or hyperosmotic solution, suggesting ERK1/2 activation occurs prior to WNK activation in the sequence of signaling events. Taken together, the evidence indicates that activation of TRPV1 is a critical early step in a signaling mechanism that responds to a hyperosmotic stimulus, possibly lens shrinkage. By activating ERK1/2 and WNK, TRPV1 activation leads to NKCC1 phosphorylation and stimulation of NKCC1-mediated ion transport.
- Shahidullah, M., Mandal, A., & Delamere, N. A. (2017). A Role for Calcium-Activated Adenylate Cyclase and Protein Kinase A in the Lens Src Family Kinase and Na,K-ATPase Response to Hyposmotic Stress. Investigative ophthalmology & visual science, 58(11), 4447-4456.More infoNa,K-ATPase activity in lens epithelium is subject to control by Src family tyrosine kinases (SFKs). Previously we showed hyposmotic solution causes an SFK-dependent increase in Na,K-ATPase activity in the epithelium. Here we explored the role of cAMP in the signaling mechanism responsible for the SFK and Na,K-ATPase response.
- Shahidullah, M., Mandal, A., & Delamere, N. A. (2017). Src Family Kinase Links Insulin Signaling to Short Term Regulation of Na,K-ATPase in Nonpigmented Ciliary Epithelium. Journal of cellular physiology, 232(6), 1489-1500.More infoInsulin has been shown to elicit changes of Na,K-ATPase activity in various tissues. Na,K-ATPase in the nonpigmented ciliary epithelium (NPE) plays a role in aqueous humor secretion and changes of Na,K-ATPase activity impact the driving force. Because we detect a change of NPE Na,K-ATPase activity in response to insulin, studies were carried out to examine the response mechanism. Ouabain-sensitive rubidium (Rb) uptake by cultured NPE cells, measured as a functional index of Na,K-ATPase-mediated inward potassium transport, was found to increase in cells exposed for 5 min to insulin. The maximally effective concentration was 100 nM. An intrinsic increase of Na,K-ATPase activity evident as a >2-fold increase in the rate of ouabain-sensitive ATP hydrolysis in homogenates obtained from cells exposed to 100 nM insulin for 5 min was also observed. Insulin-treated cells exhibited Akt, Src family kinase (SFK), ERK1/2, and p38 activation, all of which were prevented by a pI3 kinase inhibitor LY294002. The Rb uptake and Na,K-ATPase activity response to insulin both were abolished by PP2, an SFK inhibitor which also prevented p38 and ERK1/2 but not Akt activation. The Akt inhibitor MK-2206 did not change the Na,K-ATPase response to insulin. The findings suggest insulin activates pI3K-dependent Akt and SFK signaling pathways that are separate. ERK1/2 and p38 activation is secondary to and dependent on SFK activation. The increase of Na,K-ATPase activity is dependent on activation of the SFK pathway. The findings are consistent with previous studies that indicate a link between Na,K-ATPase activity and SFK signaling. J. Cell. Physiol. 232: 1489-1500, 2017. © 2016 Wiley Periodicals, Inc.
- Delamere, N. A., Mandal, A., & Shahidullah, M. (2016). The Significance of TRPV4 Channels and Hemichannels in the Lens and Ciliary Epithelium. Journal of ocular pharmacology and therapeutics : the official journal of the Association for Ocular Pharmacology and Therapeutics, 32(8), 504-508.More infoTo function normally, all cells must maintain ion homeostasis, establish a membrane potential, and regulate water content. These actions require active Na-K transport provided by Na,K-ATPase. The lens, however, is made up almost entirely of fiber cells that have little or no Na,K-ATPase activity. Lens ion and water homeostasis rely on Na,K-ATPase activity in a small number of cells at the periphery of epithelium monolayer. Therefore, the function of the epithelium must be integrated with the needs of the fiber mass. This suggests that a remote control mechanism may adjust Na,K-ATPase activity to match increases or decreases of ion leakage, which may occur a considerable distance away. Here, we review evidence that TRPV4 channels in the epithelium become activated when the lens is subjected to osmotic- or damage-induced swelling. This triggers a chain of events in the lens epithelium that opens connexin hemichannels, allowing ATP release that stimulates purinergic receptors, activates Src family tyrosine kinases, and increases Na,K-ATPase activity. Recent studies also revealed functional connexin hemichannels along with TRPV4 channels in nonpigmented ciliary epithelial (NPE) cells that secrete aqueous humor into the eye. Because TRPV4 channels are mechanosensitive, we speculate they might enable the NPE to respond to stimuli such as mechanical distortion associated with volume homeostasis during fluid transfer across the ciliary epithelium or changes in intraocular pressure.
- Lee, J., Shahidullah, M., Hotchkiss, A., Coca-Prados, M., Delamere, N. A., & Pelis, R. M. (2015). A renal-like organic anion transport system in the ciliary epithelium of the bovine and human eye. Molecular pharmacology, 87(4), 697-705.More infoThe purpose of this study was to determine the direction of organic anion (OA) transport across the ciliary body and the transport proteins that may contribute. Transport of several OAs across the bovine ciliary body was examined using ciliary body sections mounted in Ussing chambers and a perfused eye preparation. Microarray, reverse-transcription polymerase chain reaction (RT-PCR), immunoblotting, and immunohistochemistry were used to examine OA transporter expression in human ocular tissues. Microarray analysis showed that many OA transporters common to other barrier epithelia are expressed in ocular tissues. mRNA (RT-PCR) and protein (immunoblotting) for OAT1, OAT3, NaDC3, and MRP4 were detected in extracts of the human ciliary body from several donors. OAT1 and OAT3 localized to basolateral membranes of nonpigmented epithelial cells and MRP4 to basolateral membranes of pigmented cells in the human eye. Para-aminohippurate (PAH) and estrone-3-sulfate transport across the bovine ciliary body in the Ussing chambers was greater in the aqueous humor-to-blood direction than in the blood-to-aqueous humor direction, and active. There was little net directional movement of cidofovir. Probenecid (0.1 mM) or novobiocin (0.1 mM) added to the aqueous humor side of the tissue, or MK571 (5-(3-(2-(7-chloroquinolin-2-yl)ethenyl)phenyl)-8-dimethylcarbamyl-4,6-dithiaoctanoic acid; 0.1 mM) added to the blood side significantly reduced net active PAH transport. The rate of 6-carboxyfluorescein elimination from the aqueous humor of the perfused eye was reduced 80% when novobiocin (0.1 mM) was present in the aqueous humor. These data indicate that the ciliary body expresses a variety of OA transporters, including those common to the kidney. They are likely involved in clearing potentially harmful endobiotic and xenobiotic OAs from the eye.
- Mandal, A., Shahidullah, M., & Delamere, N. A. (2015). Calcium entry via connexin hemichannels in lens epithelium. Experimental eye research, 132C, 52-58.More infoExposure to hyposmotic solution causes release of ATP from lens cells via hemichannels. Because hemichannel opening feasibly could swamp the cells with calcium, we carried out studies to measure the magnitude of the increase in cytoplasmic calcium concentration caused by hemichannel opening. In studies on porcine lens epithelial cells in primary culture, propidium iodide (PI) uptake was measured as an index of hemichannel opening. PI uptake was increased significantly in cells exposed to hyposmotic solution. The PI increase under hyposmotic conditions was suppressed by GAP 27, a connexin inhibitor peptide. In studies on cells loaded with Fura-2, continuous exposure to hyposmotic solution caused a cytoplasmic calcium concentration increase that peaked within ∼30 s then remained elevated at or below the peak response for more than 60 min. The peak calcium concentration was 186 ± 2.3 nM compared to a baseline value of 98.0 ± 1.4 nM. The calcium concentration increased a lot further in cells exposed to A23187 (2.5 μM) or the sodium-calcium exchange inhibitor SN-6 (10 μM) added after the onset of the calcium rise in hyposmotic solution. The cytoplasmic calcium increase in hyposmotic solution was abolished by GAP 27. Calcium returned to baseline in cells exposed to hyposmotic solution then treated with GAP 27 starting 2 min after the onset of the calcium rise. The calcium increase in hyposmotic solution did not occur when calcium was eliminated from the bathing medium. The responses to hyposmotic and hyperosmotic stress were different. There was no detectable increase in calcium or PI entry in cells exposed to hyperosmotic solution (500mOsm). In summary, GAP 27-sensitive accumulation of PI by cultured lens epithelium points to connexin hemichannel opening and associated calcium entry. Even though connexins form channels with a large carrying capacity, calcium entry does not increase the cytoplasmic calcium concentration beyond a tolerable physiological range.
- Shahidullah, M., Mandal, A., & Delamere, N. A. (2015). Damage to lens fiber cells causes TRPV4-dependent Src family kinase activation in the epithelium. Experimental eye research, 140, 85-93.More infoThe bulk of the lens consists of tightly packed fiber cells. Because mature lens fibers lack mitochondria and other organelles, lens homeostasis relies on a monolayer of epithelial cells at the anterior surface. The detection of various signaling pathways in lens epithelial cells suggests they respond to stimuli that influence lens function. Focusing on Src Family Kinases (SFKs) and Transient Receptor Potential Vanilloid 4 (TRPV4), we tested whether the epithelium can sense and respond to an event that occurs in fiber mass. The pig lens was subjected to localized freeze-thaw (FT) damage to fibers at posterior pole then the lens was incubated for 1-10 min in Krebs solution at 37 °C. Transient SFK activation in the epithelium was detectable at 1 min. Using a western blot approach, the ion channel TRPV4 was detected in the epithelium but was sparse or absent in fiber cells. Even though TRPV4 expression appears low at the actual site of FT damage to the fibers, SFK activation in the epithelium was suppressed in lenses subjected to FT damage then incubated with the TRPV4 antagonist HC067047 (10 μM). Na,K-ATPase activity was examined because previous studies report changes of Na,K-ATPase activity associated with SFK activation. Na,K-ATPase activity doubled in the epithelium removed from FT-damaged lenses and the response was prevented by HC067047 or the SFK inhibitor PP2 (10 μM). Similar changes were observed in response to fiber damage caused by injection of 5 μl hyperosmotic NaCl or mannitol solution beneath the surface of the posterior pole. The findings point to a TRPV4-dependent mechanism that enables the epithelial cells to detect remote damage in the fiber mass and respond within minutes by activating SFK and increasing Na,K-ATPase activity. Because TRPV4 channels are mechanosensitive, we speculate they may be stimulated by swelling of the lens structure caused by damage to the fibers. Increased Na,K-ATPase activity gives the lens greater capacity to control ion concentrations in the fiber mass and the Na,K-ATPase response may reflect the critical contribution of the epithelium to lens ion homeostasis.
- Beckel, J. M., Argall, A. J., Lim, J. C., Xia, J., Lu, W., Coffey, E. E., Macarak, E. J., Shahidullah, M., Delamere, N. A., Zode, G. S., Sheffield, V. C., Shestopalov, V. I., Laties, A. M., & Mitchell, C. H. (2015). Mechanosensitive release of adenosine 5'-triphosphate through pannexin channels and mechanosensitive upregulation of pannexin channels in optic nerve head astrocytes: a mechanism for purinergic involvement in chronic strain. Glia, 62(9), 1486-501.More infoAs adenosine 5'-triphosphate (ATP) released from astrocytes can modulate many neural signaling systems, the triggers and pathways for this ATP release are important. Here, the ability of mechanical strain to trigger ATP release through pannexin channels and the effects of sustained strain on pannexin expression were examined in rat optic nerve head astrocytes. Astrocytes released ATP when subjected to 5% of equibiaxial strain or to hypotonic swelling. Although astrocytes expressed mRNA for pannexins 1-3, connexin 43, and VNUT, pharmacological analysis suggested a predominant role for pannexins in mechanosensitive ATP release, with Rho kinase contribution. Astrocytes from panx1(-/-) mice had reduced baseline and stimulated levels of extracellular ATP, confirming the role for pannexins. Swelling astrocytes triggered a regulatory volume decrease that was inhibited by apyrase or probenecid. The swelling-induced rise in calcium was inhibited by P2X7 receptor antagonists A438079 and AZ10606120, in addition to apyrase and carbenoxolone. Extended stretch of astrocytes in vitro upregulated expression of panx1 and panx2 mRNA. A similar upregulation was observed in vivo in optic nerve head tissue from the Tg-MYOC(Y437H) mouse model of chronic glaucoma; genes for panx1, panx2, and panx3 were increased, whereas immunohistochemistry confirmed increased expression of pannexin 1 protein. In summary, astrocytes released ATP in response to mechanical strain, with pannexin 1 the predominant efflux pathway. Sustained strain upregulated pannexins in vitro and in vivo. Together, these findings provide a mechanism by which extracellular ATP remains elevated under chronic mechanical strain, as found in the optic nerve head of patients with glaucoma.
- Delamere, N. A., Shahidullah, M., J, B. M., M, A. J., C, L. J., & J, X. (2014). Mechanosensitive release of adenosine 5'-triphosphate pannexin channels and mechanosensitive upregulation of pannexin channels in potic nerve head astrocytes: A mechanism for purinergic involvement in chronic strain..
- Delamere, N. A., Shahidullah, M., J, B. M., M, A. J., C, L. J., & J, X. (2014). Mechanosensitive release of adenosine 5'-triphosphate pannexin channels and mechanosensitive upregulation of pannexin channels in potic nerve head astrocytes: A mechanism for purinergic involvement in chronic strain.. Glia.
- Shahidullah, M., & Delamere, N. A. (2014). Connexins form functional hemichannels in porcine ciliary epithelium. Experimental eye research, 118, 20-9.More infoThe expression of connexins in the ciliary epithelium is consistent with gap junctions between the pigmented (PE) and nonpigmented ciliary epithelium (NPE) that form when connexon hemichannels from adjacent cells pair to form a channel. Here we present evidence that suggests undocked connexons may form functional hemichannels that permit exchange of substances between NPE and the aqueous humor. Intact porcine eyes were perfused via the ciliary artery and propidium iodide (PI) (MW 668) was added to the aqueous humor compartment as a tracer. After calcium-free solution containing PI was introduced into the aqueous humor compartment for 30 min, fluorescence microscopy revealed PI in the NPE cell layer. PI entry into the NPE was inhibited by calcium and by the connexin antagonist 18α-glycyrrhetinic acid (18-AGA). Studies also were carried out with cultured porcine NPE. Under normal conditions, little PI entered the cultured cells but calcium-free medium stimulated PI accumulation and the entry was inhibited by 18-AGA. In cells loaded with calcein (MW 622), calcium-free solution stimulated calcein exit. 18-AGA partially suppressed calcein exit in calcium-free medium. Connexin 43 and connexin 50 proteins were detected by western blot analysis in both native and cultured NPE. In the intact eye, immunolocalization studies revealed connexin 50 at the basolateral, aqueous humor-facing, margin of the NPE. In contrast, connexin 43 was observed at the junction of the PE and NPE layer and on the basolateral membrane of PE. The results point to functional hemichannels at the NPE basolateral surface. It is feasible that hemichannels might contribute to the transfer of substances between the ciliary epithelium cytoplasm and aqueous humor.
- Shahidullah, M., Mandal, A., Wei, G., & Delamere, N. A. (2014). Nitric oxide regulation of Na, K-ATPase activity in ocular ciliary epithelium involves Src family kinase. Journal of cellular physiology, 229(3), 343-52.More infoThe nitric oxide (NO) donor sodium nitroprusside (SNP) is known to reduce aqueous humor (AH) secretion in the isolated porcine eye. Previously, SNP was found to inhibit Na,K-ATPase activity in nonpigmented ciliary epithelium (NPE), AH-secreting cells, through a cGMP/protein kinase G (PKG)-mediated pathway. Here we show Src family kinase (SFK) activation in the Na,K-ATPase activity response to SNP. Ouabain-sensitive (86) Rb uptake was reduced by >35% in cultured NPE cells exposed to SNP (100 µM) or exogenously added cGMP (8-Br-cGMP) (100 µM) and the SFK inhibitor PP2 (10 µM) prevented the response. Ouabain-sensitive ATP hydrolysis was reduced by ~40% in samples detected in material obtained from SNP- and 8-Br-cGMP-treated cells following homogenization, pointing to an intrinsic change of Na,K-ATPase activity. Tyrosine-10 phosphorylation of Na,K-ATPase α1 subunit was detected in SNP and L-arginine-treated cells and the response prevented by PP2. SNP elicited an increase in cell cGMP. Cells exposed to 8-Br-cGMP displayed SFK activation (phosphorylation) and inhibition of both ouabain-sensitive (86) Rb uptake and Na,K-ATPase activity that was prevented by PP2. SFK activation, which also occurred in SNP-treated cells, was suppressed by inhibitors of soluble guanylate cyclase (ODQ; 10 µM) and PKG (KT5823; 1 µM). SNP and 8-Br-cGMP also increased phosphorylation of ERK1/2 and p38 MAPK and the response prevented by PP2. However, U0126 did not prevent SNP or 8-Br-cGMP-induced inhibition of Na,K-ATPase activity. Taken together, the results suggest that NO activates guanylate cyclase to cause a rise in cGMP and subsequent PKG-dependent SFK activation. Inhibition of Na,K-ATPase activity depends on SFK activation.
- Shahidullah, M., Mandal, A., Wei, G., Levin, L. R., Buck, J., & Delamere, N. A. (2014). Nonpigmented ciliary epithelial cells respond to acetazolamide by a soluble adenylyl cyclase mechanism. Investigative ophthalmology & visual science, 55(1), 187-97.More infoThe nonpigmented ciliary epithelium (NPE) is rich in soluble adenylyl cyclase (sAC), a proposed cytoplasmic bicarbonate sensor. Here, we examine the contribution of sAC to an increase in cyclic AMP (cAMP) and changes in a key ion transporter, H(+)-ATPase, in NPE exposed to acetazolamide, a carbonic anhydrase inhibitor (CAI).
- Delamere, N. A., Burt, J. M., Mandal, A., Shahidullah, M., & Ek Vitorin, J. F. (2018, Fall). Opening for common goals: the transient (calcium) connection of TRP and Cx channels. 2018 Arizona Physiological Society (AZPS) Annual Meeting. Tempe AZ: AZPS.