U-73122 inhibits carbachol-induced increases in [Ca2+]i, IP3, and insulin release in beta-TC3 cells

We studied the effects of the aminosteroid U-73122, a putative phospholipase C (PLC) inhibitor, on carbachol-induced increases in insulin release, [Ca2+]i, and IP3 in beta-TC3 cells. Carbachol (0.1-100 microM) increased [Ca2+]i and carbachol (0.1-1000 microM) increased insulin release dose-dependently. Carbachol (100 microM) also increased inositol 1,4,5-trisphosphate (IP3) production. U-73122 (2-12 microM) inhibited the effects of carbachol on [Ca2+]i and insulin release in a dose-dependent manner, and at the highest dose studied (12 microM) it abolished or greatly attenuated all three effects of carbachol. In contrast, U-73343 (12 microM), the analog of U-73122 that does not inhibit PLC, only inhibited the effect of carbachol on [Ca2+]i by 20%, and did not inhibit the effect of carbachol on insulin release. Since carbachol increases IP3, [Ca2+]i, and insulin release by activating PLC, these results suggested that U-73122 inhibits phospholipase C-dependent processes in beta-TC3 cells.