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Schmidt G, Rienas G, Müller S, Richter K, Sander M, Koch C, Henrich M. A fixed 20:1 combination of cafedrine/theodrenaline increases cytosolic Ca 2+ concentration in human tracheal epithelial cells via ryanodine receptor-mediated Ca 2+ release. Sci Rep 2023; 13:16216. [PMID: 37758747 PMCID: PMC10533847 DOI: 10.1038/s41598-023-43342-0] [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: 04/10/2023] [Accepted: 09/22/2023] [Indexed: 09/29/2023] Open
Abstract
Mucociliary clearance is a pivotal physiological mechanism that protects the lung by cleaning the airways from pollution and colonization, thereby preventing infection. Ciliary function is influenced by various signal transduction cascades, and Ca2+ represents a key second messenger. A fixed 20:1 combination of cafedrine and theodrenaline has been widely used to treat perioperative hypotension and emergency hypotensive states since the 1960s; however, its effect on the intracellular Ca2+ concentration ([Ca2+]i) of respiratory epithelium remains unknown. Therefore, human tracheal epithelial cells were exposed to the clinically applied 20:1 mixture of cafedrine/theodrenaline and the individual substances separately. [Ca2+]i was assessed by FURA-2 340/380 fluorescence ratio. Pharmacological inhibitors were applied to elucidate relevant signal transduction cascades, and reverse transcription polymerase chain reaction (RT-PCR) was performed on murine tracheal epithelium to analyze ryanodine receptor (RyR) subtype expression. All three pharmacological preparations instantaneously induced a steep increase in [Ca2+]i that quickly returned to its baseline value despite the persistence of each substance. Peak [Ca2+]i following the administration of 20:1 cafedrine/theodrenaline, cafedrine alone, and theodrenaline alone increased in a dose-dependent manner, with median effective concentrations of 0.35 mM (7.32 mM cafedrine and 0.35 mM theodrenaline), 3.14 mM, and 3.45 mM, respectively. When extracellular Ca2+ influx was inhibited using a Ca2+-free buffer solution, the peak [Ca2+]i following the administration of cafedrine alone and theodrenaline alone were reduced but not abolished. No alteration in [Ca2+]i compared with baseline [Ca2+]i was observed during β-adrenergic receptor inhibition. Depletion of caffeine-sensitive stores and inhibition of RyR, but not IP3 receptors, completely abolished any increase in [Ca2+]i. However, [Ca2+]i still increased following the depletion of mitochondrial Ca2+ stores using 2,4-dinitrophenol. RT-PCR revealed RyR-2 and RyR-3 expression on murine tracheal epithelium. Although our experiments showed that cafedrine/theodrenaline, cafedrine alone, or theodrenaline alone release Ca2+ from intracellular stores through mechanisms that are exclusively triggered by β-adrenergic receptor stimulation, which most probably lead to RyR activation, clinical plasma concentrations are considerably lower than those used in our experiments to elicit an increase in [Ca2+]i; therefore, further studies are needed to evaluate the ability of cafedrine/theodrenaline to alter mucociliary clearance in clinical practice.
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Affiliation(s)
- Götz Schmidt
- Department of Anesthesiology, Operative Intensive Care Medicine and Pain Therapy, Justus Liebig University of Giessen, Rudolf-Buchheim-Strasse 7, 35392, Giessen, Germany.
| | - Gerrit Rienas
- Department of Anesthesiology, Operative Intensive Care Medicine and Pain Therapy, Justus Liebig University of Giessen, Rudolf-Buchheim-Strasse 7, 35392, Giessen, Germany
| | - Sabrina Müller
- Department of Anesthesiology, Operative Intensive Care Medicine and Pain Therapy, Justus Liebig University of Giessen, Rudolf-Buchheim-Strasse 7, 35392, Giessen, Germany
| | - Katrin Richter
- Department of General and Thoracic Surgery, Justus Liebig University of Giessen, Rudolf-Buchheim-Strasse 7, 35392, Giessen, Germany
| | - Michael Sander
- Department of Anesthesiology, Operative Intensive Care Medicine and Pain Therapy, Justus Liebig University of Giessen, Rudolf-Buchheim-Strasse 7, 35392, Giessen, Germany
| | - Christian Koch
- Department of Anesthesiology, Operative Intensive Care Medicine and Pain Therapy, Justus Liebig University of Giessen, Rudolf-Buchheim-Strasse 7, 35392, Giessen, Germany
| | - Michael Henrich
- Department of Anesthesiology, Intensive Care Medicine, Emergency Medicine, Vidia St. Vincentius-Clinic Karlsruhe gAG, Karlsruhe, Germany
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Ozawa T. Elucidation of the ryanodine-sensitive Ca2+ release mechanism of rat pancreatic acinar cells: modulation by cyclic ADP-ribose and FK506. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2004; 1693:159-66. [PMID: 15363629 DOI: 10.1016/j.bbamcr.2004.04.003] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/18/2003] [Revised: 03/01/2004] [Accepted: 04/16/2004] [Indexed: 10/26/2022]
Abstract
The effects of cyclic ADP-ribose (cADPR) and the immunosuppressant drug FK506 on microsomal Ca2+ release through a ryanodine-sensitive mechanism were investigated in rat pancreatic acinar cells. After a steady state of 45Ca2+ uptake into the microsomal vesicles, ryanodine or caffeine was added. Preincubation of the vesicles with cADPR (0.5 microM) shifted the dose-response curve of ryanodine- or caffeine-induced 45Ca2+ release from the vesicles to the left. Preincubation with cADPR shifted the dose-response curve of the FK506-induced 45Ca2+ release upward. Preincubation with FK506 (3 microM) shifted the dose-response curve of the ryanodine- or caffeine-induced 45Ca2+ release to the left by the same extent as that in the case of cADPR. FK506 shifted the dose-response curve of the cADPR-induced 45Ca2+ release upward. The presence of both cADPR and FK506 enhanced the ryanodine (30 microM)- or caffeine (10 mM)-induced 45Ca2+ release by the same extent as that in the case of cADPR alone or FK506 alone. These results indicate that cADPR and FK506 modulate the ryanodine-sensitive Ca2+ release mechanism of rat pancreatic acinar cells by increasing the ryanodine or caffeine sensitivity to the mechanism. In addition, there is a possibility that the mechanisms of modulation by cADPR and FK506 are the same.
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Affiliation(s)
- Terutaka Ozawa
- Department of Physiology, Graduate School of Medicine, Tohoku University, Seiryo-machi 2-1, Aoba-ku, Sendai 980-8575, Japan.
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Abstract
An impressive array of cytosolic calcium ([Ca2+](i)) signals exert control over a broad range of physiological processes. The specificity and fidelity of these [Ca2+](i) signals is encoded by the frequency, amplitude, and sub-cellular localization of the response. It is believed that the distinct characteristics of [Ca2+](i) signals underlies the differential activation of effectors and ultimately cellular events. This "shaping" of [Ca2+](i) signals can be achieved by the influence of additional signaling pathways modulating the molecular machinery responsible for generating [Ca2+](i) signals. There is a particularly rich source of potential sites of crosstalk between the cAMP and the [Ca2+](i) signaling pathways. This review will focus on the predominant molecular loci at which these classical signaling systems interact to impact the spatio-temporal pattern of [Ca2+](i) signaling in non-excitable cells.
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Affiliation(s)
- Jason I E Bruce
- Department of Pharmacology & Physiology, School of Medicine and Dentistry, University of Rochester Medical Center, 601 Elmwood Avenue, Rochester, NY 14642, USA.
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Tsuboi T, da Silva Xavier G, Holz GG, Jouaville LS, Thomas AP, Rutter GA. Glucagon-like peptide-1 mobilizes intracellular Ca2+ and stimulates mitochondrial ATP synthesis in pancreatic MIN6 beta-cells. Biochem J 2003; 369:287-99. [PMID: 12410638 PMCID: PMC1223096 DOI: 10.1042/bj20021288] [Citation(s) in RCA: 159] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2002] [Revised: 09/25/2002] [Accepted: 10/31/2002] [Indexed: 11/17/2022]
Abstract
Glucagon-like peptide-1 (GLP-1) is a potent regulator of glucose-stimulated insulin secretion whose mechanisms of action are only partly understood. In the present paper, we show that at low (3 mM) glucose concentrations, GLP-1 increases the free intramitochondrial concentrations of both Ca(2+) ([Ca(2+)](m)), and ATP ([ATP](m)) in clonal MIN6 beta-cells. Suggesting that cAMP-mediated release of Ca(2+) from intracellular stores is responsible for these effects, increases in [ATP](m) that were induced by GLP-1 were completely blocked by the Rp isomer of adenosine-3',5'-cyclic monophosphothioate (Rp-cAMPS), or by chelation of intracellular Ca(2+). Furthermore, inhibition of Ins(1,4,5) P (3) (IP(3)) receptors with xestospongin C, or application of ryanodine, partially inhibited GLP-1-induced [ATP](m) increases, and the simultaneous blockade of both IP(3) and ryanodine receptors (RyR) completely eliminated the rise in [ATP](m). GLP-1 appeared to prompt Ca(2+)-induced Ca(2+) release through IP(3) receptors via a protein kinase A (PKA)-mediated phosphorylation event, since ryanodine-insensitive [ATP](m) increases were abrogated with the PKA inhibitor, H89. In contrast, the effects of GLP-1 on RyR-mediated [ATP](m) increases were apparently mediated by the cAMP-regulated guanine nucleotide exchange factor cAMP-GEFII, since xestospongin C-insensitive [ATP](m) increases were blocked by a dominant-negative form of cAMP-GEFII (G114E,G422D). Taken together, these results demonstrate that GLP-1 potentiates glucose-stimulated insulin release in part via the mobilization of intracellular Ca(2+), and the stimulation of mitochondrial ATP synthesis.
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Affiliation(s)
- Takashi Tsuboi
- Henry Wellcome Laboratories for Integrated Cell Signalling, Department of Biochemistry, School of Medical Sciences, University of Bristol, University Walk, Bristol BS8 1TD, U.K
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Bruce JIE, Shuttleworth TJ, Giovannucci DR, Yule DI. Phosphorylation of inositol 1,4,5-trisphosphate receptors in parotid acinar cells. A mechanism for the synergistic effects of cAMP on Ca2+ signaling. J Biol Chem 2002; 277:1340-8. [PMID: 11694504 DOI: 10.1074/jbc.m106609200] [Citation(s) in RCA: 124] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Acetylcholine-evoked secretion from the parotid gland is substantially potentiated by cAMP-raising agonists. A potential locus for the action of cAMP is the intracellular signaling pathway resulting in elevated cytosolic calcium levels ([Ca(2+)](i)). This hypothesis was tested in mouse parotid acinar cells. Forskolin dramatically potentiated the carbachol-evoked increase in [Ca(2+)](i), converted oscillatory [Ca(2+)](i) changes into a sustained [Ca(2+)](i) increase, and caused subthreshold concentrations of carbachol to increase [Ca(2+)](i) measurably. This potentiation was found to be independent of Ca(2+) entry and inositol 1,4,5-trisphosphate (InsP(3)) production, suggesting that cAMP-mediated effects on Ca(2+) release was the major underlying mechanism. Consistent with this hypothesis, dibutyryl cAMP dramatically potentiated InsP(3)-evoked Ca(2+) release from streptolysin-O-permeabilized cells. Furthermore, type II InsP(3) receptors (InsP(3)R) were shown to be directly phosphorylated by a protein kinase A (PKA)-mediated mechanism after treatment with forskolin. In contrast, no evidence was obtained to support direct PKA-mediated activation of ryanodine receptors (RyRs). However, inhibition of RyRs in intact cells, demonstrated a role for RyRs in propagating Ca(2+) oscillations and amplifying potentiated Ca(2+) release from InsP(3)Rs. These data indicate that potentiation of Ca(2+) release is primarily the result of PKA-mediated phosphorylation of InsP(3)Rs, and may largely explain the synergistic relationship between cAMP-raising agonists and acetylcholine-evoked secretion in the parotid. In addition, this report supports the emerging consensus that phosphorylation at the level of the Ca(2+) release machinery is a broadly important mechanism by which cells can regulate Ca(2+)-mediated processes.
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Affiliation(s)
- Jason I E Bruce
- Department of Pharmacology & Physiology, School of Medicine and Dentistry, University of Rochester Medical Center, Rochester, New York 14642, USA.
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Kang G, Chepurny OG, Holz GG. cAMP-regulated guanine nucleotide exchange factor II (Epac2) mediates Ca2+-induced Ca2+ release in INS-1 pancreatic beta-cells. J Physiol 2001; 536:375-85. [PMID: 11600673 PMCID: PMC2278885 DOI: 10.1111/j.1469-7793.2001.0375c.xd] [Citation(s) in RCA: 169] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
1. The signal transduction pathway responsible for cAMP-dependent Ca2+-induced Ca2+ release (CICR) from endoplasmic reticulum Ca2+ stores was assessed in the insulin-secreting cell line INS-1. 2. CICR was triggered by the GLP-1 receptor agonist exendin-4, an effect mimicked by caffeine, Sp-cAMPS or forskolin. CICR required influx of Ca2+ through L-type voltage-dependent Ca2+ channels, and was blocked by treatment with nimodipine, thapsigargin, or ryanodine, but not by the IP3 receptor antagonist xestospongin C. 3. Treatment with the cAMP antagonist 8-Br-Rp-cAMPS blocked CICR in response to exendin-4, whereas the PKA inhibitor H-89 was ineffective when tested at a concentration demonstrated to inhibit PKA-dependent gene expression. 4. RT-PCR of INS-1 cells demonstrated expression of mRNA coding for the type-II isoform of cAMP-regulated guanine nucleotide exchange factor (cAMP-GEF-II, Epac2). 5. CICR in response to forskolin was blocked by transient transfection and expression of a dominant negative mutant isoform of cAMP-GEF-II in which inactivating mutations were introduced into the exchange factor's two cAMP-binding domains. 6. It is concluded that CICR in INS-1 cells results from GLP-1 receptor-mediated sensitization of the intracellular Ca2+ release mechanism, a signal transduction pathway independent of PKA, but which requires cAMP-GEF-II.
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Affiliation(s)
- G Kang
- Department of Physiology and Neuroscience, New York University School of Medicine, New York, NY 10016, USA
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Chou CL, Yip KP, Michea L, Kador K, Ferraris JD, Wade JB, Knepper MA. Regulation of aquaporin-2 trafficking by vasopressin in the renal collecting duct. Roles of ryanodine-sensitive Ca2+ stores and calmodulin. J Biol Chem 2000; 275:36839-46. [PMID: 10973964 DOI: 10.1074/jbc.m005552200] [Citation(s) in RCA: 176] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In the renal collecting duct, vasopressin increases osmotic water permeability (P(f)) by triggering trafficking of aquaporin-2 vesicles to the apical plasma membrane. We investigated the role of vasopressin-induced intracellular Ca(2+) mobilization in this process. In isolated inner medullary collecting ducts (IMCDs), vasopressin (0.1 nm) and 8-(4-chlorophenylthio)-cAMP (0.1 mm) elicited marked increases in [Ca(2+)](i) (fluo-4). Vasopressin-induced Ca(2+) mobilization was completely blocked by preloading with the Ca(2+) chelator BAPTA. In parallel experiments, BAPTA completely blocked the vasopressin-induced increase in P(f) without affecting adenosine 3',5'-cyclic monophosphate (cAMP) production. Previously, we demonstrated the lack of activation of the phosphoinositide-signaling pathway by vasopressin in IMCD, suggesting an inositol 1,4,5-trisphosphate-independent mechanism of Ca(2+) release. Evidence for expression of the type 1 ryanodine receptor (RyR1) in IMCD was obtained by immunofluorescence, immunoblotting, and reverse transcription-polymerase chain reaction. Ryanodine (100 microm), a ryanodine receptor antagonist, blocked the arginine vasopressin-mediated increase in P(f) and blocked vasopressin-stimulated redistribution of aquaporin-2 to the plasma membrane domain in primary cultures of IMCD cells, as assessed by immunofluorescence immunocytochemistry. Calmodulin inhibitors (W7 and trifluoperazine) blocked the P(f) response to vasopressin and the vasopressin-stimulated redistribution of aquaporin-2. The results suggest that Ca(2+) release from ryanodine-sensitive stores plays an essential role in vasopressin-mediated aquaporin-2 trafficking via a calmodulin-dependent mechanism.
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Affiliation(s)
- C L Chou
- Laboratory of Kidney and Electrolyte Metabolism, NHLBI, National Institutes of Health, Bethesda, Maryland 20892, USA
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8
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Watson EL, Jacobson KL, Singh JC, Idzerda R, Ott SM, DiJulio DH, Wong ST, Storm DR. The type 8 adenylyl cyclase is critical for Ca2+ stimulation of cAMP accumulation in mouse parotid acini. J Biol Chem 2000; 275:14691-9. [PMID: 10799557 DOI: 10.1074/jbc.275.19.14691] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Capacitative Ca(2+) entry stimulates cAMP synthesis in mouse parotid acini, suggesting that one of the Ca(2+)-sensitive adenylyl cyclases (AC1 or AC8) may play an important role in the regulation of parotid function (Watson, E. L., Wu, Z., Jacobson, K. L., Storm, D. R., Singh, J. C., and Ott, S. M. (1998) Am. J. Physiol. 274, C557-C565). To evaluate the role of AC1 and AC8 in Ca(2+) stimulation of cAMP synthesis in parotid cells, acini were isolated from AC1 mutant (AC1-KO) and AC8 mutant (AC8-KO) mice and analyzed for Ca(2+) stimulation of intracellular cAMP levels. Although Ca(2+) stimulation of intracellular cAMP levels in acini from AC1-KO mice was indistinguishable from wild type mice, acini from AC8-KO mice showed no Ca(2+)-stimulated cAMP accumulation. This indicates that AC8, but not AC1, plays a major role in coupling Ca(2+) signals to cAMP synthesis in parotid acini. Interestingly, treatment of acini from AC8-KO mice with agents, i.e. carbachol and thapsigargin that increase intracellular Ca(2+), lowered cAMP levels. This decrease was dependent upon Ca(2+) influx and independent of phosphodiesterase activation. Immunoblot analysis revealed that AC5/6 and AC3 are expressed in parotid glands. Inhibition of calmodulin (CaM) kinase II with KN-62, or inclusion of the CaM inhibitor, calmidazolium, did not prevent agonist-induced inhibition of stimulated cAMP accumulation. In vitro studies revealed that Ca(2+), independently of CaM, inhibited isoproterenol-stimulated AC. Data suggest that agonist augmentation of stimulated cAMP levels is due to activation of AC8 in mouse parotid acini, and strongly support a role for AC5/6 in the inhibition of stimulated cAMP levels.
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Affiliation(s)
- E L Watson
- Department of Oral Biology, University of Washington, Seattle, Washington 98195, USA.
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Ozawa T. Ryanodine-sensitive Ca(2+) release mechanism of rat pancreatic acinar cells is modulated by calmodulin. BIOCHIMICA ET BIOPHYSICA ACTA 1999; 1452:254-62. [PMID: 10590314 DOI: 10.1016/s0167-4889(99)00135-4] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
The effects of calmodulin (CaM) and CaM antagonists on microsomal Ca(2+) release through a ryanodine-sensitive mechanism were investigated in rat pancreatic acinar cells. When caffeine (10 mM) was added after a steady state of ATP-dependent (45)Ca(2+) uptake into the microsomal vesicles, the caffeine-induced (45)Ca(2+) release was significantly increased by pretreatment with ryanodine (10 microM). The presence of W-7 (60 microM), a potent inhibitor of CaM, strongly inhibited the release, while W-5 (60 microM), an inactive CaM antagonist, showed no inhibition. Inhibition of the release by W-7 was observed at all caffeine concentrations (5-30 mM) tested. The presence of exogenously added CaM (10 microg/ml) markedly increased the caffeine (5-10 mM)-induced (45)Ca(2+) release and shifted the dose-response curve of caffeine-induced (45)Ca(2+) release to the left. Cyclic ADP-ribose (cADPR, 2 microM)-induced (45)Ca(2+) release was enhanced by the presence of ryanodine (10 microM). cADPR (2 microM)- or ryanodine (500 microM)-induced (45)Ca(2+) release was also inhibited by W-7 (60 microM), but not by W-5 (60 microM), and was stimulated by CaM (10 microg/ml). These results suggest that the ryanodine-sensitive Ca(2+) release mechanism of rat pancreatic acinar cells is modulated by CaM.
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Affiliation(s)
- T Ozawa
- Department of Physiology, Tohoku University School of Medicine Seiryocho 2-1, Aoba-ku, Sendai, Japan
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Holz GG, Leech CA, Heller RS, Castonguay M, Habener JF. cAMP-dependent mobilization of intracellular Ca2+ stores by activation of ryanodine receptors in pancreatic beta-cells. A Ca2+ signaling system stimulated by the insulinotropic hormone glucagon-like peptide-1-(7-37). J Biol Chem 1999; 274:14147-56. [PMID: 10318832 PMCID: PMC3508791 DOI: 10.1074/jbc.274.20.14147] [Citation(s) in RCA: 164] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Glucagon-like peptide-1 (GLP-1) is an intestinally derived insulinotropic hormone currently under investigation for use as a novel therapeutic agent in the treatment of type 2 diabetes mellitus. In vitro studies of pancreatic islets of Langerhans demonstrated that GLP-1 interacts with specific beta-cell G protein-coupled receptors, thereby facilitating insulin exocytosis by raising intracellular levels of cAMP and Ca2+. Here we report that the stimulatory influence of GLP-1 on Ca2+ signaling results, in part, from cAMP-dependent mobilization of ryanodine-sensitive Ca2+ stores. Studies of human, rat, and mouse beta-cells demonstrate that the binding of a fluorescent derivative of ryanodine (BODIPY FL-X ryanodine) to its receptors is specific, reversible, and of high affinity. Rat islets and BTC3 insulinoma cells are shown by reverse transcriptase polymerase chain reaction analyses to express mRNA corresponding to the type 2 isoform of ryanodine receptor-intracellular Ca2+ release channel (RYR2). Single-cell measurements of [Ca2+]i using primary cultures of rat and human beta-cells indicate that GLP-1 facilitates Ca2+-induced Ca2+ release (CICR), whereby mobilization of Ca2+ stores is triggered by influx of Ca2+ through L-type Ca2+ channels. In these cells, GLP-1 is shown to interact with metabolism of D-glucose to produce a fast transient increase of [Ca2+]i. This effect is reproduced by 8-Br-cAMP, but is blocked by a GLP-1 receptor antagonist (exendin-(9-39)), a cAMP antagonist ((Rp)-cAMPS), an L-type Ca2+ channel antagonist (nimodipine), an antagonist of the sarco(endo)plasmic reticulum Ca2+ ATPase (thapsigargin), or by ryanodine. Characterization of the CICR mechanism by voltage clamp analysis also demonstrates a stimulation of Ca2+ release by caffeine. These findings provide new support for a model of beta-cell signal transduction whereby GLP-1 promotes CICR by sensitizing intracellular Ca2+ release channels to the stimulatory influence of cytosolic Ca2+.
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Affiliation(s)
- G G Holz
- Diabetes Unit, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts 02114, USA.
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