ABSTRACT
AIM: To investigate the changes in intracellular potassium activity(a iK) and membrane potential(V_m) induced by low external sodium infusion (Low _o) and to detect the mechanisms involved and the relationship between a iK and V_m. METHODS: a iK and V_m were measured in infusion with different sodium concentrations using methods of convenient and ion selective microelectrodes in guinea pig ventricular myocardium. RESULTS: Low _o resulted in a decrease in a iK and an increase in V_m in a Na + concentration-dependent manner.At the same time,contraction and resting potential increased, and action potential duration decreased markedly,but action potential amplitude was not affected. A change of the pH from 7.4 to 7.0 in low _o solution reduced the decrease in a iK, but did not affect the increase in V_m. CONCLUSION: A better linear relationship appeared between the changes in a ik and _o or in V_m and _o,while during each low _o the change in both a iK or V_m may reach a new balance level.