Electrophysiology of Stimulus-Secretion Coupling in Human β-Cells

Herein, we review the applicability to human β-cells of an electrophysiologically based hypothesis of the coupling of glucose metabolism to insulin secretion. According to this hypothesis, glucose metabolism leads to the generation of intracellular intermediates (including ATP), which leads to closure of ATP-sensitive K⁺ channels. Channel closure results in membrane depolarization, the onset of electrical activity, and voltage-dependent Ca²⁺ entry. The resultant rise in cytosolic Ca²⁺ leads to Ca²⁺-dependent exocytosis of insulin granules. We found that most of the published experimental evidence for human β-cells supports this hypothesis. In addition, we present three other emerging lines of evidence in support of this hypothesis for human islet β-cells: 1) the effects of pH¹-altering maneuvers on insulin secretion and electrical activity; 2) preliminary identification of LVA and HVA single Ca²⁺ channel currents; and 3) validation of the feasibility of C^m measurements to track insulin granule exocytosis. On the basis of this last new line of evidence, we suggest that combinations of C^m measurements and electrical activity/membrane current measurements may help define the roles of diverse electrical activity patterns, displayed by human β-cells, in stimulus-induced insulin secretion.