POSSIBLE ROLE OF CALCIUM-RELEASE FROM THE SARCOPLASMIC-RETICULUM IN PACEMAKING IN GUINEA-PIG SINOATRIAL NODE

Ryanodine and cyclopiazonic acid were used to alter the ability of the sarcoplasmic reticulum (SR) to store calcium. interventions of this k ind significantly reduced the rate of spontaneous beating of guinea-pi g sino-atrial node preparations. In addition, both of these drugs decr eased the rate of rise and modified other characteristics of the actio n potentials recorded from this region. It is proposed that calcium re leased from the SR plays an important, previously unrecognized, role i n pacemaking in the sino-atrial node, possibly through regulation of s arcolemmal ionic currents.