Phosphocreatine as a determinant of K(ATP) channel activity in pancreatic beta-cells.

The aim of the present study was to test the hypothesis that a creatine kinase/phosphocreatine system is involved in the regulation of K(ATP) channels in pancreatic beta-cells. The phosphocreatine concentration in isolated mouse islets clearly increased in parallel with the ATP/ADP ratio in response to a rise of the glucose concentration from 0.5 mM to 15 mM. The currents through K(ATP) channels expressed in oocytes of Xenopus laevis were inhibited by injection of phosphocreatine or ATP but not by phosphate or creatine alone. In inside-out patches of beta-cell membranes obtained from native beta-cells, phosphocreatine reduced the open probability of single K(ATP) channels in the presence of ADP but not in the absence of the nucleotide. These experiments suggest the existence of a K(ATP) channel-associated creatine kinase that phosphorylates ADP. The creatine kinase inhibitor iodoacetamide suppressed the glucose-induced oscillations of the cytoplasmic Ca(2+) concentration, [Ca(2+)](c). It is concluded that phosphocreatine serves as a shuttle for energy-rich phosphate from the mitochondria to the plasma membrane. The data provide a novel model for signal transduction to K(ATP) channels in pancreatic beta-cells.