PACHYMATISMA JOHNSTONII EXTRACT OPENS ATP-SENSITIVE POTASSIUM CHANNELS IN CARDIAC MYOCYTES OF THE FROG-HEART

The effects of a proteic extract (PachyTX), isolated from the sponge P achymatisma johnstonii, were studied respectively with intracellular m icroelectrode and the ''whole cell'' patch clamp techniques on fibers and myocytes isolated from the sinoatrial region of frog heart. PachyT X significantly and reversibly shortened the action potential duration and decreased the stimulated peak contraction. Under voltage clamp, P achyTX increased, in a dose-dependent manner, a tetraethylammonium-ins ensitive but glibenclamide-inhibited outward current. This current fai led to develop when adenosine 5'-triphosphate (ATP) was intracellularl y applied to the cell by diffusion through the patch electrode. PachyT X mimics the effect of the ATP-sensitive K channel opener SR 44866 on frog atrial action potential and peak contraction. From this evidence, it can be concluded that PachyTX is a new natural potent opener of AT P-sensitive K channels in frog atrial heart muscle and that the openin g of these channels is associated with the inhibition of the contracti on of cardiac muscle. (C) 1994 Academic Press, Inc.