Does galanin inhibit insulin secretion by opening of the ATP-regulated K⁺ channel in the β-cell?

The intrapancreatic neuropeptide galanin potently inhibits glucose-induced insulin secretion. This effect is in part due to a repolarization of the β-cells and ensuring reduction in the cytoplasmic free Ca²⁺ concentration, [Ca²⁺]_i. We propose that galanin inhibition of β-cell action potentials is associated with the appearance of ATP-regulated K⁺ channels. Galanin opens K⁺ channels in a patch membrane when applied to the external solution in the cell-attached patch configuration. However, galanin does not detectably increase K⁺ permeability during whole-cell experiments, even when GTP was included in the internal solution. Our findings are not consistent with a direct effect of galanin on the K⁺ channels, but rather indicate that the effect of the neuropeptide is mediated by some intracellular coupling factor(s).