Long-term inhibition of protein tyrosine kinase impairs electrophysiologic activity and a rapid component of exocytosis in pancreatic β-cells

Dysfunction of pancreatic beta-cells is a fundamental feature in the pathogenesis of type 2 diabetes. As insulin receptor signaling occurs via protein tyrosine kinase (PTK), we investigated the role of PTK activity in the etiology of beta-cell dysfunction by inhibiting PTK activity in primary cultured mouse pancreatic beta-cells and INS-1 cells with genistein treatment over 24 h. Electrophysiologic recordings showed genistein treatment significantly attenuated ATP-sensitive K+ (K-ATP) and voltage-dependent Ca2+ currents, and depolarized the resting membrane potential in primary beta-cells. When stimulated by high glucose, genistein-treated P-cells exhibited a time delay of both depolarization and Ca2+ influx, and were unable to fire action potentials, as well as displaying a reduced level of Ca2+ influx and a loss of Ca2+ oscillations. Semiquantitative PCR analysis revealed decreased expression of K-ATP and L-type Ca2+ channel mRNA in genistein-treated islets. PTK inhibition also significantly reduced the rapid component of secretory vesicle exocytosis, as indicated by membrane capacitance measurements, and this is likely to be due to the reduced Ca2+ current amplitude in these cells. These results illustrate that compromised PTK activity contributes to pancreatic P-cell dysfunction and may be involved in the etiology of type 2 diabetes.