Possible Involvement of Transient Receptor Potential Channels in Electrophile-Induced Insulin Secretion from RINm5F Cells

Abstract

Endogenously produced reactive oxygen species reportedly stimulate insulin secretion from islet β-cells. However, the molecular machinery that governs the oxidant-induced insulin secretion has yet to be determined. The present study demonstrates, using rat islet β-cell-derived RINm5F cells, the involvement of the transient receptor potential (TRP) cation channels in the insulin secretion induced by the lipid peroxidation product 4-hydroxy-2-nonenal. Short-term (1 h) exposure of 4-hydroxy-2-nonenal induced a transient increase in intracellular Ca²⁺ concentration and subsequent insulin secretion in a concentration-dependent manner. The increase in intracellular Ca²⁺ concentration seemed to be due to an influx through the L-type voltage-dependent Ca²⁺ channel, since it was not observed when extracellular Ca²⁺ was absent and was inhibited almost completely by diltiazem or nifedipine. Ruthenium red, a non-specific inhibitor of TRP channels, inhibited the Ca²⁺ influx and insulin secretion evoked by 4-hydroxy-2-nonenal. Among the TRP channels, TRPA1 was found to be predominantly expressed, not only in RINm5F cells, but also rat islets. TRPA1 agonists, allylisothiocyanate and 15-deoxy-Δ^12,14-prostaglandin J₂, significantly induced Ca²⁺ influx, and a specific inhibitor TRPA1, HC-030031, blocked the effects elicited by 4-hydroxy-2-nonenal. These results suggest that 4-hydroxy-2-nonenal induces Ca²⁺ influx via the activation of TRP channels, including TRPA1, which appears to be coupled with the L-type voltage-dependent Ca²⁺ channel, and ultimately insulin secretion in RINm5F cells.