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Takeyasu M, Kozai K, Sugita M. Involvement of sodium-glucose cotransporter-1 activities in maintaining oscillatory Cl - currents from mouse submandibular acinar cells. J Comp Physiol B 2024; 194:21-32. [PMID: 38308715 PMCID: PMC10940492 DOI: 10.1007/s00360-024-01532-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2023] [Revised: 12/01/2023] [Accepted: 01/04/2024] [Indexed: 02/05/2024]
Abstract
In salivary acinar cells, cholinergic stimulation induces elevations of cytosolic [Ca2+]i to activate the apical exit of Cl- through TMEM16A Cl- channels, which acts as a driving force for fluid secretion. To sustain the Cl- secretion, [Cl-]i must be maintained to levels that are greater than the electrochemical equilibrium mainly by Na+-K+-2Cl- cotransporter-mediated Cl- entry in basolateral membrane. Glucose transporters carry glucose into the cytoplasm, enabling the cells to produce ATP to maintain Cl- and fluid secretion. Sodium-glucose cotransporter-1 is a glucose transporter highly expressed in acinar cells. The salivary flow is suppressed by the sodium-glucose cotransporter-1 inhibitor phlorizin. However, it remains elusive how sodium-glucose cotransporter-1 contributes to maintaining salivary fluid secretion. To examine if sodium-glucose cotransporter-1 activity is required for sustaining Cl- secretion to drive fluid secretion, we analyzed the Cl- currents activated by the cholinergic agonist, carbachol, in submandibular acinar cells while comparing the effect of phlorizin on the currents between the whole-cell patch and the gramicidin-perforated patch configurations. Phlorizin suppressed carbachol-induced oscillatory Cl- currents by reducing the Cl- efflux dependent on the Na+-K+-2Cl- cotransporter-mediated Cl- entry in addition to affecting TMEM16A activity. Our results suggest that the sodium-glucose cotransporter-1 activity is necessary for maintaining the oscillatory Cl- secretion supported by the Na+-K+-2Cl- cotransporter activity in real time to drive fluid secretion. The concerted effort of sodium-glucose cotransporter-1, Na+-K+-2Cl- cotransporter, and apically located Cl- channels might underlie the efficient driving of Cl- secretion in different secretory epithelia from a variety of animal species.
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Affiliation(s)
- Misa Takeyasu
- Department of Physiology and Oral Physiology, Graduate School of Biomedical and Health Sciences, Hiroshima University, Kasumi 1-2-3, Minami-ku, Hiroshima, 734-8553, Japan
- Department of Pediatric Dentistry, Graduate School of Biomedical and Health Sciences, Hiroshima University, Hiroshima, Japan
| | - Katsuyuki Kozai
- Department of Pediatric Dentistry, Graduate School of Biomedical and Health Sciences, Hiroshima University, Hiroshima, Japan
| | - Makoto Sugita
- Department of Physiology and Oral Physiology, Graduate School of Biomedical and Health Sciences, Hiroshima University, Kasumi 1-2-3, Minami-ku, Hiroshima, 734-8553, Japan.
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Kusuda Y, Kondo Y, Miyagi Y, Munemasa T, Hori Y, Aonuma F, Tsuka S, Mukaibo T, Masaki C, Hosokawa R. Long-term dexamethasone treatment diminishes store-operated Ca 2+ entry in salivary acinar cells. Int J Oral Sci 2019; 11:1. [PMID: 30602784 PMCID: PMC6315037 DOI: 10.1038/s41368-018-0031-0] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2017] [Revised: 05/10/2018] [Accepted: 05/14/2018] [Indexed: 11/09/2022] Open
Abstract
Corticosteroids are used in the treatment of many diseases; however, they also induce various side effects. Dexamethasone is one of the most potent corticosteroids, and it has been reported to induce the side effect of impaired salivary gland function. This study aimed to evaluate the effects of dexamethasone on mouse submandibular gland function to gain insight into the mechanism of dexamethasone-induced salivary hypofunction. The muscarinic agonist carbachol (CCh) induced salivary secretion and was not affected by short-term dexamethasone treatment but was decreased following long-term dexamethasone administration. The expression levels of the membrane proteins Na+-K+-2Cl- cotransporter, transmembrane member 16A, and aquaporin 5 were comparable between the control and long-term dexamethasone treatment groups. The CCh-induced increase in calcium concentration was significantly lower in the presence of extracellular Ca2+ in the long-term dexamethasone treatment group compared to that in the control group. Furthermore, CCh-induced salivation in the absence of extracellular Ca2+ and Ca2+ ionophore A23187-induced salivation was comparable between the control and long-term dexamethasone treatment groups. Moreover, salivation induced by the Ca2+-ATPase inhibitor thapsigargin was diminished in the long-term dexamethasone treatment group. In summary, these results demonstrate that short-term dexamethasone treatment did not impair salivary gland function, whereas long-term dexamethasone treatment diminished store-operated Ca2+ entry, resulting in hyposalivation in mouse submandibular glands.
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Affiliation(s)
- Yuichiro Kusuda
- Division of Oral Reconstruction and Rehabilitation, Kyushu Dental University, Kitakyushu, Fukuoka, 803-8580, Japan
| | - Yusuke Kondo
- Division of Oral Reconstruction and Rehabilitation, Kyushu Dental University, Kitakyushu, Fukuoka, 803-8580, Japan.
| | - Yuta Miyagi
- Division of Oral Reconstruction and Rehabilitation, Kyushu Dental University, Kitakyushu, Fukuoka, 803-8580, Japan
| | - Takashi Munemasa
- Division of Oral Reconstruction and Rehabilitation, Kyushu Dental University, Kitakyushu, Fukuoka, 803-8580, Japan
| | - Yusuke Hori
- Division of Oral Reconstruction and Rehabilitation, Kyushu Dental University, Kitakyushu, Fukuoka, 803-8580, Japan
| | - Fumiko Aonuma
- Division of Oral Reconstruction and Rehabilitation, Kyushu Dental University, Kitakyushu, Fukuoka, 803-8580, Japan
| | - Shintaro Tsuka
- Division of Oral Reconstruction and Rehabilitation, Kyushu Dental University, Kitakyushu, Fukuoka, 803-8580, Japan
| | - Taro Mukaibo
- Division of Oral Reconstruction and Rehabilitation, Kyushu Dental University, Kitakyushu, Fukuoka, 803-8580, Japan
| | - Chihiro Masaki
- Division of Oral Reconstruction and Rehabilitation, Kyushu Dental University, Kitakyushu, Fukuoka, 803-8580, Japan
| | - Ryuji Hosokawa
- Division of Oral Reconstruction and Rehabilitation, Kyushu Dental University, Kitakyushu, Fukuoka, 803-8580, Japan
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Nezu A, Morita T, Nagai T, Tanimura A. Simultaneous monitoring of Ca 2+ responses and salivary secretion in live animals reveals a threshold intracellular Ca 2+ concentration for salivation. Exp Physiol 2018; 104:61-69. [PMID: 30367746 DOI: 10.1113/ep086868] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/25/2017] [Accepted: 10/25/2018] [Indexed: 12/21/2022]
Abstract
NEW FINDINGS What is the central question of this study? The effects of Ca2+ responses on salivary fluid secretion have been studied indirectly by monitoring ion channel activities and other indices. Therefore, Ca2+ responses during salivary secretion remain poorly understood. What is the main finding and its importance? Herein, we developed a simultaneous monitoring system for Ca2+ responses and salivary secretion in live animals using a YC-Nano50-expressing submandibular gland and a fibre-optic pressure sensor. This new approach revealed a clear time lag between the onset of Ca2+ responses and salivary secretion. We also estimated the [Ca2+ ]i and provided direct evidence for the regulation of salivary secretion by small increases in [Ca2+ ]i in submandibular gland acinar cells. ABSTRACT We monitored changes in [Ca2+ ]i during salivary secretion in the rat submandibular gland in live animals using a combination of intravital Ca2+ imaging with the ultrasensitive Ca2+ indicator YC-Nano50 and a fibre-optic pressure sensor. Intravenous infusion of ACh (10-720 nmol min-1 ) increased [Ca2+ ]i and salivary flow rate in a dose-dependent manner. Repetitive stimulation with ACh induced equivalent Ca2+ responses and salivary secretion in the same individual animals. The accurate ACh stimulation experiments revealed a clear time lag between the onset of the increase in [Ca2+ ]i and salivary secretion. The time lag with the lowest dose of ACh (30 nmol min-1 ) was 106 s, which shortened to 19 s with the dose used for maximal salivary secretion (360 nmol min-1 ). This time lag might reflect the time required for [Ca2+ ]i to reach the level required to activate molecules for fluid secretion. The resting [Ca2+ ]i in submandibular gland was 37 nm, and [Ca2+ ]i at the onset of salivary secretion was 45-57 nm, irrespective of ACh dose. These results indicate that low [Ca2+ ]i is sufficient to trigger fluid secretion in the rat submandibular gland in vivo.
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Affiliation(s)
- Akihiro Nezu
- Department of Pharmacology, School of Dentistry, Health Sciences University of Hokkaido, Ishikari-Tobetsu, Hokkaido, 061-0293, Japan
| | - Takao Morita
- Department of Biochemistry, The Nippon Dental University School of Life Dentistry at Niigata, 1-8 Hamaura-cho, Chuo-ku, Niigata, 951-8580, Japan
| | - Takeharu Nagai
- Institute of Scientific and Industrial Research, Osaka University, 8-1 Mihogaoka, Ibaraki, Osaka, 567-0047, Japan
| | - Akihiko Tanimura
- Department of Pharmacology, School of Dentistry, Health Sciences University of Hokkaido, Ishikari-Tobetsu, Hokkaido, 061-0293, Japan
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Terachi M, Hirono C, Kitagawa M, Sugita M. The biphasic effect of extracellular glucose concentration on carbachol-induced fluid secretion from mouse submandibular glands. Eur J Oral Sci 2018; 126:197-205. [PMID: 29676804 DOI: 10.1111/eos.12417] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Cholinergic agonists evoke elevations of the cytoplasmic free-calcium concentration ([Ca2+ ]i ) to stimulate fluid secretion in salivary glands. Salivary flow rates are significantly reduced in diabetic patients. However, it remains elusive how salivary secretion is impaired in diabetes. Here, we used an ex vivo submandibular gland perfusion technique to characterize the dependency of salivary flow rates on extracellular glucose concentration and activities of glucose transporters expressed in the glands. The cholinergic agonist carbachol (CCh) induced sustained fluid secretion, the rates of which were modulated by the extracellular glucose concentration in a biphasic manner. Both lowering the extracellular glucose concentration to less than 2.5 mM and elevating it to higher than 5 mM resulted in decreased CCh-induced fluid secretion. The CCh-induced salivary flow was suppressed by phlorizin, an inhibitor of the sodium-glucose cotransporter 1 (SGLT1) located basolaterally in submandibular acinar cells, which is altered at the protein expression level in diabetic animal models. Our data suggest that SGLT1-mediated glucose uptake in acinar cells is required to maintain the fluid secretion by sustaining Cl- secretion in real-time. High extracellular glucose levels may suppress the CCh-induced secretion of salivary fluid by altering the activities of ion channels and transporters downstream of [Ca2+ ]i signals.
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Affiliation(s)
- Momomi Terachi
- Department of Physiology and Oral Physiology, Graduate School of Biomedical & Health Sciences, Hiroshima University, Hiroshima, Japan
| | - Chikara Hirono
- Department of Physiology and Oral Physiology, Graduate School of Biomedical & Health Sciences, Hiroshima University, Hiroshima, Japan
| | - Michinori Kitagawa
- Department of Physiology and Oral Physiology, Graduate School of Biomedical & Health Sciences, Hiroshima University, Hiroshima, Japan
| | - Makoto Sugita
- Department of Physiology and Oral Physiology, Graduate School of Biomedical & Health Sciences, Hiroshima University, Hiroshima, Japan
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Delpire E, Gagnon KB. Na + -K + -2Cl - Cotransporter (NKCC) Physiological Function in Nonpolarized Cells and Transporting Epithelia. Compr Physiol 2018; 8:871-901. [PMID: 29687903 DOI: 10.1002/cphy.c170018] [Citation(s) in RCA: 47] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Two genes encode the Na+ -K+ -2Cl- cotransporters, NKCC1 and NKCC2, that mediate the tightly coupled movement of 1Na+ , 1K+ , and 2Cl- across the plasma membrane of cells. Na+ -K+ -2Cl- cotransport is driven by the chemical gradient of the three ionic species across the membrane, two of them maintained by the action of the Na+ /K+ pump. In many cells, NKCC1 accumulates Cl- above its electrochemical potential equilibrium, thereby facilitating Cl- channel-mediated membrane depolarization. In smooth muscle cells, this depolarization facilitates the opening of voltage-sensitive Ca2+ channels, leading to Ca2+ influx, and cell contraction. In immature neurons, the depolarization due to a GABA-mediated Cl- conductance produces an excitatory rather than inhibitory response. In many cell types that have lost water, NKCC is activated to help the cells recover their volume. This is specially the case if the cells have also lost Cl- . In combination with the Na+ /K+ pump, the NKCC's move ions across various specialized epithelia. NKCC1 is involved in Cl- -driven fluid secretion in many exocrine glands, such as sweat, lacrimal, salivary, stomach, pancreas, and intestine. NKCC1 is also involved in K+ -driven fluid secretion in inner ear, and possibly in Na+ -driven fluid secretion in choroid plexus. In the thick ascending limb of Henle, NKCC2 activity in combination with the Na+ /K+ pump participates in reabsorbing 30% of the glomerular-filtered Na+ . Overall, many critical physiological functions are maintained by the activity of the two Na+ -K+ -2Cl- cotransporters. In this overview article, we focus on the functional roles of the cotransporters in nonpolarized cells and in epithelia. © 2018 American Physiological Society. Compr Physiol 8:871-901, 2018.
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Affiliation(s)
- Eric Delpire
- Department of Anesthesiology, Vanderbilt University Medical School, Nashville, Tennessee, USA
| | - Kenneth B Gagnon
- Division of Nephrology and Hypertension, Department of Medicine, University of Louisville School of Medicine, Louisville, Keystone, USA
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6
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Evaluation of the relationship between salivation ability and blood flow velocity in the submandibular gland using pulsed Doppler ultrasonography. Oral Radiol 2012. [DOI: 10.1007/s11282-012-0102-4] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
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Bansal P, Wang S, Liu S, Xiang YY, Lu WY, Wang Q. GABA coordinates with insulin in regulating secretory function in pancreatic INS-1 β-cells. PLoS One 2011; 6:e26225. [PMID: 22031825 PMCID: PMC3198728 DOI: 10.1371/journal.pone.0026225] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2011] [Accepted: 09/22/2011] [Indexed: 11/18/2022] Open
Abstract
Pancreatic islet β-cells produce large amounts of γ-aminobutyric acid (GABA), which is co-released with insulin. GABA inhibits glucagon secretion by hyperpolarizing α-cells via type-A GABA receptors (GABA(A)Rs). We and others recently reported that islet β-cells also express GABA(A)Rs and that activation of GABA(A)Rs increases insulin release. Here we investigate the effects of insulin on the GABA-GABA(A)R system in the pancreatic INS-1 cells using perforated-patch recording. The results showed that GABA produces a rapid inward current and depolarizes INS-1 cells. However, pre-treatment of the cell with regular insulin (1 µM) suppressed the GABA-induced current (I(GABA)) by 43%. Zinc-free insulin also suppressed I(GABA) to the same extent of inhibition by regular insulin. The inhibition of I(GABA) occurs within 30 seconds after application of insulin. The insulin-induced inhibition of I(GABA) persisted in the presence of PI3-kinase inhibitor, but was abolished upon inhibition of ERK, indicating that insulin suppresses GABA(A)Rs through a mechanism that involves ERK activation. Radioimmunoassay revealed that the secretion of C-peptide was enhanced by GABA, which was blocked by pre-incubating the cells with picrotoxin (50 µM, p<0.01) and insulin (1 µM, p<0.01), respectively. Together, these data suggest that autocrine GABA, via activation of GABA(A)Rs, depolarizes the pancreatic β-cells and enhances insulin secretion. On the other hand, insulin down-regulates GABA-GABA(A)R signaling presenting a feedback mechanism for fine-tuning β-cell secretion.
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Affiliation(s)
- Paul Bansal
- Departments of Physiology and Medicine, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada
- Division of Endocrinology and Metabolism, The Keenan Research Centre in the Li Ka-Shing Knowledge Institute, St. Michael's Hospital, Toronto, Ontario, Canada
| | - Shuanglian Wang
- Department of Physiology and Pharmacology, University of Western Ontario, London, Ontario, Canada
- Robarts Research Institute, University of Western Ontario, London, Ontario, Canada
| | - Shenghao Liu
- Departments of Physiology and Medicine, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada
- Division of Endocrinology and Metabolism, The Keenan Research Centre in the Li Ka-Shing Knowledge Institute, St. Michael's Hospital, Toronto, Ontario, Canada
| | - Yun-Yan Xiang
- Department of Physiology and Pharmacology, University of Western Ontario, London, Ontario, Canada
- Robarts Research Institute, University of Western Ontario, London, Ontario, Canada
| | - Wei-Yang Lu
- Department of Physiology and Pharmacology, University of Western Ontario, London, Ontario, Canada
- Robarts Research Institute, University of Western Ontario, London, Ontario, Canada
- * E-mail: (W-YL); (QW)
| | - Qinghua Wang
- Departments of Physiology and Medicine, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada
- Division of Endocrinology and Metabolism, The Keenan Research Centre in the Li Ka-Shing Knowledge Institute, St. Michael's Hospital, Toronto, Ontario, Canada
- * E-mail: (W-YL); (QW)
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Montalbetti N, Fischbarg J. Frequency spectrum of transepithelial potential difference reveals transport-related oscillations. Biophys J 2009; 97:1530-7. [PMID: 19751657 PMCID: PMC2741586 DOI: 10.1016/j.bpj.2009.05.063] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2009] [Revised: 05/18/2009] [Accepted: 05/28/2009] [Indexed: 11/24/2022] Open
Abstract
How epithelia transport fluid is a fundamental issue that is unresolved. Explanations offered include molecular engines, local transcellular osmosis, local paracellular osmosis, and paracellular fluid transport. On the basis of experimental and theoretical work done on corneal endothelium, a fluid transporting epithelium, we suggest electroosmotic coupling at the level of the intercellular junctions driven by the transendothelial electrical potential difference as an explanation of paracellular fluid transport. We collect frequency spectra of that potential difference in real-time. For what we believe is the first time for any epithelium, we report that, unexpectedly, the potential difference displays oscillations at many characteristic frequencies. We also show that on both stimulating cell activity and inhibiting ion transport mechanisms, there are corresponding changes in the oscillations amplitudes that mirror changes known previously in rates of fluid transport. We believe these findings provide a novel tool to study the kinetics of electrogenic elements such as channels and transporters, which from this evidence would give rise to current oscillations with characteristic periods going from 150 ms to 8 s.
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Affiliation(s)
| | - Jorge Fischbarg
- Institute of Cardiology Research, University of Buenos Aires, and CONICET, Buenos Aires, Argentina
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Shintani T, Hirono C, Sugita M, Iwasa Y, Shiba Y. Suppression of carbachol-induced oscillatory Cl- secretion by forskolin in rat parotid and submandibular acinar cells. Am J Physiol Gastrointest Liver Physiol 2008; 294:G738-47. [PMID: 18187520 DOI: 10.1152/ajpgi.00239.2007] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Sympathetic stimulation induces weak salivation compared with parasympathetic stimulation. To clarify this phenomenon in salivary glands, we investigated cAMP-induced modulation of Ca(2+)-activated Cl(-) secretion from rat parotid and submandibular acinar cells because fluid secretion from salivary glands depends on the Cl(-) secretion. Carbachol (Cch), a Ca(2+)-increasing agent, induced hyperpolarization of the cells with oscillatory depolarization in the current clamp mode of the gramicidin-perforated patch recording. In the voltage clamp mode at -80 mV, Cch induced a bumetanide-sensitive oscillatory inward current, which was larger in rat submandibular acinar cells than in parotid acinar cells. Forskolin and IBMX, cAMP-increasing agents, did not induce any marked current, but they evoked a small nonoscillatory inward current in the presence of Cch and suppressed the Cch-induced oscillatory inward current in all parotid acinar cells and half (56%) of submandibular acinar cells. In the current clamp mode, forskolin + IBMX evoked a small nonoscillatory depolarization in the presence of Cch and reduced the amplitude of Cch-induced oscillatory depolarization in both acinar cells. The oscillatory inward current estimated at the depolarized membrane potential was suppressed by forskolin + IBMX. These results indicate that cAMP suppresses Ca(2+)-activated oscillatory Cl(-) secretion of parotid and submandibular acinar cells at -80 mV and possibly at the membrane potential during Cch stimulation. The suppression may result in the weak salivation induced by sympathetic stimulation.
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Affiliation(s)
- Takahide Shintani
- Department of Oral Physiology, Hiroshima University Graduate School of Biomedical Sciences, Minami-ku, Hiroshima 734-8553, Japan
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KONGO H, HIRONO C, SUGITA M, Iwasa Y, SHIBA Y. Involvement of cytoskeletal integrity in the regulation of Cl- and amylase secretion from rat parotid acinar cells. Biomed Res 2008; 29:131-9. [DOI: 10.2220/biomedres.29.131] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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11
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Li J, Zhang N, Ye B, Ju W, Orser B, Fox JEM, Wheeler MB, Wang Q, Lu WY. Non-steroidal anti-inflammatory drugs increase insulin release from beta cells by inhibiting ATP-sensitive potassium channels. Br J Pharmacol 2007; 151:483-93. [PMID: 17435793 PMCID: PMC2013967 DOI: 10.1038/sj.bjp.0707259] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
BACKGROUND AND PURPOSE Some non-steroidal anti-inflammatory drugs (NSAIDs) incidentally induce hypoglycemia, which is often seen in diabetic patients receiving sulphonylureas. NSAIDs influence various ion channel activities, thus they may cause hypoglycemia by affecting ion channel functions in insulin secreting beta cells. This study investigated the effects of the NSAID meclofenamic acid (MFA) on the electrical excitability and the secretion of insulin from pancreatic beta cells. EXPERIMENTAL APPROACH Using patch clamp techniques and insulin secretion assays, the effects of MFA on the membrane potential and transmembrane current of INS-1 cells, and insulin secretion were studied. KEY RESULTS Under perforated patch recordings, MFA induced a rapid depolarization in INS-1 cells bathed in low (2.8 mM), but not high (28 mM) glucose solutions. MFA, as well as acetylsalicylic acid (ASA) and flufenamic acid (FFA), excited the cells by inhibiting ATP-sensitive potassium channels (K(ATP)). In whole cell recordings, K(ATP) conductance consistently appeared when intracellular ATP was diluted. Intracellular glibenclamide prevented the development of K(ATP) activity, whereas intracellular MFA had no effect. At low glibenclamide concentrations, MFA induced additional inhibition of the K(ATP) current. Live cell Ca(2+) imaging displayed that MFA elevated intracellular Ca(2+) at low glucose concentrations. Furthermore, MFA dose-dependently increased insulin release under low, but not high, glucose conditions. CONCLUSIONS AND IMPLICATIONS MFA blocked K(ATP) through an extracellular mechanism and thus increased insulin secretion. As some NSAIDs synergistically inhibit K(ATP) activity together with sulphonylureas, the risk of NSAID-induced hypoglycemia should be considered when glucose-lowering compounds are administered.
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Affiliation(s)
- J Li
- Department of Anesthesia, Sunnybrook Health Sciences Centre, University of Toronto Toronto, Ontario, Canada
- Department of Anesthesia, University of Toronto Toronto, Ontario, Canada
| | - N Zhang
- Division of Endocrinology & Metabolism, St Michael's Hospital, University of Toronto Toronto, Ontario, Canada
| | - B Ye
- Department of Anesthesia, Sunnybrook Health Sciences Centre, University of Toronto Toronto, Ontario, Canada
| | - W Ju
- Department of Physiology, University of Toronto Toronto, Ontario, Canada
| | - B Orser
- Department of Anesthesia, University of Toronto Toronto, Ontario, Canada
- Department of Physiology, University of Toronto Toronto, Ontario, Canada
| | - J E M Fox
- Department of Physiology, University of Toronto Toronto, Ontario, Canada
| | - M B Wheeler
- Department of Physiology, University of Toronto Toronto, Ontario, Canada
| | - Q Wang
- Division of Endocrinology & Metabolism, St Michael's Hospital, University of Toronto Toronto, Ontario, Canada
- Department of Physiology, University of Toronto Toronto, Ontario, Canada
| | - W-Y Lu
- Department of Anesthesia, Sunnybrook Health Sciences Centre, University of Toronto Toronto, Ontario, Canada
- Department of Anesthesia, University of Toronto Toronto, Ontario, Canada
- Department of Physiology, University of Toronto Toronto, Ontario, Canada
- Author for correspondence:
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12
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Hirono C. [Electrolyte transport by salivary glands]. Nihon Yakurigaku Zasshi 2006; 127:256-60. [PMID: 16755076 DOI: 10.1254/fpj.127.256] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
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13
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Blumenthal EM. Modulation of tyramine signaling by osmolality in an insect secretory epithelium. Am J Physiol Cell Physiol 2005; 289:C1261-7. [PMID: 15987771 DOI: 10.1152/ajpcell.00026.2005] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The control of water balance in multicellular organisms depends on absorptive and secretory processes across epithelia. This study concerns the effects of osmolality on the function of the Malpighian tubules (MTs), a major component of the insect excretory system. Previous work has shown that the biogenic amine tyramine increases transepithelial chloride conductance and urine secretion in Drosophila MTs. This study demonstrates that the response of MTs to tyramine, as measured by the depolarization of the transepithelial potential (TEP), is modulated by the osmolality of the surrounding medium. An increase in osmolality caused decreased tyramine sensitivity, whereas a decrease in osmolality resulted in increased tyramine sensitivity; changes in osmolality of +/-20% resulted in a nearly 10-fold modulation of the response to 10 nM tyramine. The activity of another diuretic agent, leucokinin, was similarly sensitive to osmolality, suggesting that the modulation occurs downstream of the tyramine receptor. In response to continuous tyramine signaling, as likely occurs in vivo, the TEP oscillates, and an increase in osmolality lengthened the period of these oscillations. Increased osmolality also caused a decrease in the rate of urine production; this decrease was attenuated by the tyraminergic antagonist yohimbine. A model is proposed in which this modulation of tyramine signaling enhances the conservation of body water during dehydration stress. The modulation of ligand signaling is a novel effect of osmolality and may be a widespread mechanism through which epithelia respond to changes in their environment.
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Affiliation(s)
- Edward M Blumenthal
- Department of Biological Sciences, Marquette University, PO Box 1881, Milwaukee, WI 53201-1881, USA.
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