Na(+)-Ca2+ exchange transport and pacemaker activity of the rabbit SA node.
Recent electrophysiological data have provided the evidences that background currents such as Na(+)-Ca2+ exchange can significantly modulate cardiac pacemaker activity. In this study, the effects of extracellular Na+ and Ca2+ concentrations on the pacemaker activity were investigated by measuring the intracellular Na+ activity (aiNa) with Na(+)-selective microelectrodes and the results are summarized as follows. 1) In the rabbit SA node, aiNa was 3.2 +/- 0.3 mM and mean MDP (maximal diastolic potential) was -63.3 +/- 1.4 mV. 2) Graded decreases of external Na+ concentration resulted in the loss of spontaneous beating, hyperpolarization and the decrease of aiNa. 3) An increase in extracellular Ca2+ concentration in low Na+ solution augmented the transient decrease of aiNa, about 3 minutes in low Na+ solution, until aiNa started to increase. 4) In low Na+ solution, which had extracellular Ca2+ concentration according to the calculation based on the equilibrium state of Na(+)-Ca2+ exchange, aiNa was continuously decreased. It was concluded that intracellular Na+ activity modulated by Na(+)-Ca2+ exchange could play an important role in the initiation of pacemaker potential.
Rark
S R
SR
Department of Physiology, Yonsei University College of Medicine, Seoul, Korea.
Suh
C K
CK
D000200:Action Potentials; D000818:Animals; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism* / Q000502:physiology; D004594:Electrophysiology; D005260:Female; D008297:Male; D010138:Pacemaker, Artificial; D011817:Rabbits; D012849:Sinoatrial Node / Q000378:metabolism* / Q000502:physiology; D012964:Sodium / Q000378:metabolism* / Q000502:physiology
D012964:Sodium; D002118:Calcium