Effect of protein kinase C on glucose-mediated insulin secretion in HIT-T15 cells

Abstract

Objective: To clarify the regulation of protein kinase C on glucose-mediated insulin secretion.

Main outcome measures: We examined the effect of protein kinase C on the cytosolic free Ca(2+) concentration ([Ca(2+)]i) and the activity of Ca(2+)-activated K(+) channels (K(Ca)-channel) in the insulinoma cell line, HIT-T15.

Results: Glucose at a concentration of 10 mmol/L increased the secretion of insulin. This increase was partly inhibited by 1 nmol/L staurosporine, a protein kinase C inhibitor. Staurosporine (1 nmol/L) also attenuated the glucose-induced elevations in [Ca(2+)]i. On the contrary, glibenclamide (100 nmol/L) specifically blocked ATP-sensitive K(+) channels, and increased both [Ca(2+)]i and insulin secretion, but staurosporine had no effect on them. Patch clamp studies showed that 10 mmol/L glucose almost completely blocked K(Ca) channel activity, an effect that was reversed by 1 nmol/L staurosporine. Phorbol 12-myristate 13-acetate (1 mmol/L), a protein kinase C activator, also decreased K(Ca) channel activity.

Conclusions: These results indicate that the activation of protein kinase C is involved in the glucose-induced release of insulin by modulating K(+) channel function in HIT-T15 cells.