The adenylyl cyclase inhibitor MDL-12,330A potentiates insulin secretion via blockade of Kv channels in rat pancreatic beta cells

Program: Abstracts - Orals, Featured Poster Presentations, and Posters
Session: SAT 834-867-Islet Biology
Bench to Bedside
Saturday, June 15, 2013: 1:45 PM-3:45 PM
Expo Halls ABC (Moscone Center)

Poster Board SAT-843
Xiaodong Li*, Qing Guo, Jingying Gao, Wan Zhang, Dongmei Wu, Yunfeng Liu and Yi Zhang
Shanxi Medical University, Taiyuan, China
Adenylyl cyclases (ACs) control many aspects of cellular function by regulating the synthesis of cyclic AMP (cAMP), a ubiquitous second messenger. MDL-12,330A, one of the most widely used AC inhibitors, serves as an important pharmacological tool for the study of functional role of ACs in variety of cell types. However, in the present study, we demonstrate that in pancreatic beta cells, MDL-12,330A potently blocked voltage-dependent potassium channels (Kv channels) independent of its influence on AC-cAMP pathway. Beta cells were patch-clamped in conventional whole-cell configuration and were identified by cell size (>4 pF for capacitance measurement) as well as their depolarization response to 11.1 mM glucose. Voltage-clamp experiments showed that MDL-12,330A only elicited 35% of Kv currents compare to control at 70 mV (47 pA/pF for MDL-12,330A, n=6; 136 pA/pF for control, n=12; p<0.001); while another widely used AC inhibitor, SQ 22536, did not exhibit any effect on Kv currents. We then examined whether modulation of cAMP downstream enzyme, protein kinase A(PKA), influences Kv channels. We found H89, a PKA inhibitor, did not elicit changes of Kv currents either. The results suggest that MDL-12,330A has a non-specific effect on Kv channels, which is not related to AC-cAMP signaling. In pancreatic beta cells, it has been well established that blockade of Kv channels prolongs action potential duration, resulting in enhanced electrical excitability, augmented intracellular Ca2+ level, and finally potentiated insulin secretion. We therefore performed experiments to determine if MDL-12,330A exerts similar effects in rat pancreatic beta cells. As expected, our current-clamp recordings showed that MDL-12,330A, but not SQ 22536 and H89, significantly prolonged action potential duration (72 ms for MDL-12,330A, n=6; 29 ms for control, n=5; p<0.001). Calcium imaging studies revealed that MDL-12,330A induced a significant increase in intracellular Ca2+ level in rat pancreatic beta cells, whereas SQ 22536 and H89 had no effects on intracellular Ca2+ level. Meanwhile, voltage-clamp measurements showed that MDL-12,330A did not alter calcium channel activity, implying that the augmented intracellular Ca2+ induced by MDL-12,330A is secondary to the inhibition of Kv channels rather than direct modulation of calcium channels. Furthermore, function examination demonstrated that MDL-12,330A significantly potentiated insulin secretion (1.7 fold increase over control for MDL-12,330A, p<0.05). whereas no effects on insulin secretion had been observed for SQ 22536 and H89 treatments. Taken together, our data indicate that, in pancreatic beta cells, MDL-12,330A potentiates insulin secretion, and the insulinotropic property of MDL-12,330A may be caused by inhibition of Kv currents rather than AC antagonism.

Nothing to Disclose: XL, QG, JG, WZ, DW, YL, YZ

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Sources of Research Support: This work was supported by grants to Y.Z (NSFC 81070662, 81273564) from  National Natural Science Foundation of China, and by grants from Natural Science Foundation of Shanxi Province (2012011039-8), Shanxi Scholarship Council of China (2012-046) as well as Advanced Programs of Shanxi for the Returned Overseas Chinese Scholars (2011-762). This work was also supported by a grant to Y.L from Department of Health of Shanxi Province (201201062). Y.Z was supported by Program for the Top Young Academic Leaders of Higher Learning Institutions of Shanxi.