Abstract
ObjectiveAdenylyl cyclases (ACs) play important role in regulating pancreatic beta cell growth, survival and secretion through the synthesis of cyclic AMP (cAMP). MDL-12,330A and SQ 22536 are two AC inhibitors used widely to establish the role of ACs. The goal of this study was to examine the effects of MDL-12,330A and SQ 22536 on insulin secretion and underlying mechanisms.MethodsPatch-clamp recording, Ca2+ fluorescence imaging and radioimmunoassay were used to measure outward K+ currents, action potentials (APs), intracellular Ca2+ ([Ca2+]i) and insulin secretion from rat pancreatic beta cells.ResultsMDL-12,330A (10 µmol/l) potentiated insulin secretion to 1.7 times of control in the presence of 8.3 mmol/l glucose, while SQ 22536 did not show significant effect on insulin secretion. MDL-12,330A prolonged AP durations (APDs) by inhibiting voltage-dependent K+ (KV) channels, leading to an increase in [Ca2+]i levels. It appeared that these effects induced by MDL-12,330A did not result from AC inhibition, since SQ 22536 did not show such effects. Furthermore, inhibition of the downstream effectors of AC/cAMP signaling by PKA inhibitor H89 and Epac inhibitor ESI-09, did not affect KV channels and insulin secretion.ConclusionThe putative AC inhibitor MDL-12,330A enhances [Ca2+]i and insulin secretion via inhibition of KV channels rather than AC antagonism in beta cells, suggesting that the non-specific effects is needed to be considered for the right interpretation of the experimental results using this agent in the analyses of the role of AC in cell function.
Highlights
Adenylyl cyclase (AC) is a crucial enzyme that catalyses the synthesis of cyclic AMP from ATP
The effects of cyclic AMP (cAMP) are mediated by two downstream effectors, protein kinase A (PKA) and exchange protein directly activated by cAMP (Epac) [4]
AC/cAMP signaling pathway is known important in regulating beta cell growth, survival and glucose-induced insulin secretion [5,6]. cAMP is a pivotal component that mediates the functions of some insulinotropic hormones, such as glucagon-like peptide-1 (GLP1) and glucose-dependent insulinotropic polypeptide (GIP) [7,8]
Summary
Adenylyl cyclase (AC) is a crucial enzyme that catalyses the synthesis of cyclic AMP (cAMP) from ATP. As an ubiquitous second messenger, cAMP plays key roles in a variety of fundamental cell functions ranging from cell growth and differentiation, to transcriptional regulation and apoptosis [1,2,3]. AC/cAMP signaling pathway is known important in regulating beta cell growth, survival and glucose-induced insulin secretion [5,6]. CAMP is a pivotal component that mediates the functions of some insulinotropic hormones, such as glucagon-like peptide-1 (GLP1) and glucose-dependent insulinotropic polypeptide (GIP) [7,8]. For investigating the role of AC/cAMP signaling pathway, pharmacological tools have been chosen to modulate AC activities in many studies. In the present study, the non-specific effect of MDL-12,330A on KV channels has been observed in pancreatic beta cells
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