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

The intrapancreatic neuropeptide galanin potently inhibits glucose-induced insulin secretion. This effect is in part due to a repolarization of the beta-cells and ensuring reduction in the cytoplasmic free Ca2+ concentration, [Ca2+]i. We propos that galanin inhibition of beta-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).

Demonstration of A-currents in pancreatic islet cells

Voltage-activated K+ currents resistant to TEA but blockable by 4-AP were recorded from mouse pancreatic islet cells. These currents first become observable during depolarizations to voltages more positive than -40 mV, reaching a peak amplitude of 120 +/- 34 pA at +6 mV (n = 4), display rapid turn on (tau = 3.3 +/- 1.1 ms at +6 mV) and inactivate completely within 250 ms (tau = 65 +/- 5 at +6 mV). The current is subject to steady-state inactivation. The midpoint (Vh) of the inactivation curve (h infinity) was observed at -72 +/- 2 mV. The properties of this current resemble those reported for the A-current in neurons.