Effect of Protein Kinase C on Glucose-Mediated Insulin Secretion in HIT-T15 Cells

Hiroko Akiyoshi; Yutaka Nakaya

doi:10.6092/1590-8577/372

Hiroko Akiyoshi Department of Nutrition, School of Medicine, The University of Tokushima. Tokushima City, Japan
Yutaka Nakaya Department of Nutrition, School of Medicine, The University of Tokushima. Tokushima City, Japan

DOI: https://doi.org/10.6092/1590-8577/372

Keywords: Potassium Channels, Protein Kinase C, Staurosporine

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 Ca²⁺ concentration ([Ca²⁺]_i) and the activity of Ca²⁺-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 [Ca²⁺]_i. On the contrary, glibenclamide (100 nmol/L) specifically blocked ATP-sensitive K⁺ channels, and increased both [Ca²⁺]_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.

Image: Inhibitory effects of glucose on K_Ca channels.

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