[Effects of sodium and calcium ions on the potentials of cardiac pacemaker cells in the frog].

True and latent pacemaker cells were differentiated in the frog heart sino-atrial area. Within the first 5 min in the hyposodium solution, a decrease of the overshoot and maximal velocity of depolarization occurred. The true pacemaker cells did not reveal any changes of the AP parameters within 30-60 min. The cells of true pacemaker exhibited a higher sensitivity to the hypocalcium solution. The data obtained suggested a scheme of the whole cycle of Na+, K+ and Ca2+ exchange.