Possible role of an ischemic preconditioning-like response mechanism in K(ATP) channel opener-mediated protection against streptozotocin-induced suppression of rat pancreatic islet function.

Potassium channel openers (KCOs) decrease insulin secretion from beta-cells. Some KCOs also protect against damage to beta-cell function and type 1 diabetes in animal models. Previously we have found that the KCO NNC 55-0118 counteracted islet cell dysfunction, and this was associated with a lowering of the mitochondrial membrane potential (Deltapsi). Presently we aimed to explore whether inhibition of insulin secretion per se or rather inhibition of mitochondrial function correlates to counteraction of beta-cell suppression. For this we used two novel KCOs (NNC 55-0321 and NNC 55-0462), which at certain concentrations have different actions regarding insulin secretion and the Deltapsi, with NNC 55-0321 being a potent inhibitor of Deltapsi and NNC 55-0462 being a potent inhibitor of insulin secretion. At 10 microM NNC 55-0321, but not with NNC 55-0462, the islet ATP content and ATP/ADP ratio was acutely decreased. This was accompanied by a complete protection against streptozotocin-induced suppression of islet insulin secretion using the former KCO. In cardiac research KCOs have been used to induce an ischemic preconditioning (IPC) response. In line with an IPC-like mechanism we found that NNC 55-0321 induced an initial free oxygen radical formation, PKC-epsilon isoform activation and a subsequent phosphorylation of the survival promoting factor Akt. Thus, KCOs may elicit mitochondrial events that resemble classical IPC seen in cardiomyocytes, and this could explain the enhanced islet cell function observed. KCOs with this property may be particularly interesting compounds to study as a rescue therapy during acute episodes of beta-cell suppression/destruction.