Insulin-secreting INS-1E cells express functional TRPV1 channels

We have studied whether functional TRPV1 channels exist in the INS-1E cells, a cell type used as a model for beta-cells, and in primary beta-cells from rat and human. The effects of the TRPV1 agonists capsaicin and AM404 on the intracellular free Ca2+ concentration ([Ca2+]i) in the INS-1E cells were studied by fura-2based microfluorometry. Capsaicin increased [Ca2+] i in a concentration-dependent manner, and the [Ca2+] i increase was dependent on extracellular Ca2+. AM404 also increased [Ca2+] i in the INS-1E cells. Capsazepine, a specific antagonist of TRPV1, completely blocked the capsaicin- and AM404-induced [Ca2+] i increases. Capsaicin did not increase [Ca2+] i in the primary beta-cells from rat and human. Whole cell patch clamp configuration was used to record currents across the plasma membrane in the INS-1E cells. Capsaicin elicited inward currents that were inhibited by capsazepine. Western blot analysis detected TRPV1 proteins in the INS-1E cells and the human islets. Immunohistochemistry was used to study the expression of TRPV1, but no TRPV1 protein immunoreactivity was detected in the human islet cells and the human insulinoma cells. We conclude that the INS-1E cells, but not the primary beta-cells, express functional TRPV1 channels.