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E-mail contact: michael.wheeler{at}utoronto.ca
Voltage-dependent K+ (Kv) channels negatively regulate Ca2+ entry into pancreatic β-cells by repolarizing glucose-stimulated action potentials. A role for phosphatidylinositol 3-kinase (PI3K) modulation of Kv channel function was investigated using the PI3K inhibitors wortmannin and LY294002, and LY303511, a negative control compound with respect to PI3K activity. In MIN6 insulinoma cells, wortmannin (100 nM) had no effect on whole-cell outward K+ currents, but LY294002 and LY303511 reversibly blocked currents in a dose-dependent manner (IC50=9.0±0.7 μM and 64.6±9.1 μM, respectively). Western blotting confirmed the specific inhibitory effects of LY294002 and wortmannin on insulin-stimulated PI3K activity. Kv currents in rat β-cells at near physiological temperatures were inhibited 92% by 25 μM LY294002. Kv2.1 and Kv1.4 are highly expressed in β-cells, and in Kv2.1-transfected tsA201 cells, 50 μM LY294002 and 100 μM LY303511 reversibly inhibited currents by 99% and 41%, respectively. In Kv1.4-transfected tsA201 cells, 50 μM LY294002 reduced the inactivation time constant from 73 to 18 ms. The insulinotropic properties of LY294002 and its effects in other excitable cells may be caused by inhibition of Kv currents rather than PI3K antagonism. Furthermore, LY294002 may represent a novel structure from which future Kv channel blockers may be developed.
Key words: insulin secretion · β cells · Kv channels · whole-cell and excised patch configuration · sustained and peak currents · activation and inactivation time constants
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