Yonsei Med J.  1991 Sep;32(3):223-230. 10.3349/ymj.1991.32.3.223.

Na+-Ca2+ exchange transport and pacemaker activity of the rabbit SA node

• Park SR
• Suh CK

• KMID: 1729589
• DOI: http://doi.org/10.3349/ymj.1991.32.3.223

Abstract

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.

Keyword

Rabbit; SA node; pacemaker activity; Na+-Ca2+ exchange; Na+-selective electrode; Intracelluar Na+ activity

MeSH Terms

Action Potentials
Animal
Biological Transport
Calcium/*metabolism/physiology
Electrophysiology
Female
Male
Pacemaker, Artificial
Rabbits
Sinoatrial Node/*metabolism/physiology
Sodium/*metabolism/physiology
Support, Non-U.S. Gov't