Impaired insulin secretion and glucose tolerance in beta cell-selective Ca(v)1.2 Ca2+ channel null mice.
Schulla V., Renström E., Feil R., Feil S., Franklin I., Gjinovci A., Jing X-J., Laux D., Lundquist I., Magnuson MA., Obermüller S., Olofsson CS., Salehi A., Wendt A., Klugbauer N., Wollheim CB., Rorsman P., Hofmann F.
Insulin is secreted from pancreatic beta cells in response to an elevation of cytoplasmic Ca(2+) resulting from enhanced Ca(2+) influx through voltage-gated Ca(2+) channels. Mouse beta cells express several types of Ca(2+) channel (L-, R- and possibly P/Q-type). beta cell-selective ablation of the gene encoding the L-type Ca(2+) channel subtype Ca(v)1.2 (betaCa(v)1.2(-/-) mouse) decreased the whole-cell Ca(2+) current by only approximately 45%, but almost abolished first-phase insulin secretion and resulted in systemic glucose intolerance. These effects did not correlate with any major effects on intracellular Ca(2+) handling and glucose-induced electrical activity. However, high-resolution capacitance measurements of exocytosis in single beta cells revealed that the loss of first-phase insulin secretion in the betaCa(v)1.2(-/-) mouse was associated with the disappearance of a rapid component of exocytosis reflecting fusion of secretory granules physically attached to the Ca(v)1.2 channel. Thus, the conduit of Ca(2+) entry determines the ability of the cation to elicit secretion.