The inhibitors of protein acylation, cerulenin and tunicamycin, increase voltage-dependent Ca 2+ currents in the insulin-secreting INS 832/13 cell

Abstract

As it has been suggested that protein acylation plays a role in nutrient stimulus–secretion coupling in the pancreatic β-cell, we examined the insulin-secreting INS 832/13 β-cell line for evidence that protein acylation was involved. The perforated whole-cell configuration was employed to voltage-clamp INS 832/13 cells. Voltage pulses were applied and Ca 2+ currents measured in the presence and absence of the protein acylation inhibitors cerulenin and tunicamycin. Both inhibitors enhanced the peak amplitude of I Ca,L. Both increased the peak inward current in the range between −40 and +30 mV and shifted the apparent maximum current by 10 mV in the hyperpolarizing direction without affecting the activation threshold of −40 mV. The two drugs had qualitatively and quantitatively similar effects. Steady-state activation curves revealed that cerulenin and tunicamycin shifted the activation curves in the hyperpolarization direction. Activation time constants were significantly reduced in the presence of both drugs. The Ca 2+ charge influx was increased by the drugs at all potentials tested. In contrast to these effects on the L-type Ca 2+ channel, the two inhibitors of protein acylation had no effect on the ATP-sensitive K + channel. The results suggest that protein acylation exerts a tonic inhibitory effect on L-type Ca 2+ channel function in the insulin-secreting β-cell.