[Heterogeneity of Na+/Ca2+ exchanger current across the left ventricular wall of rabbit].

Objective: To investigate the distribution characteristics of Na+/Ca2+ exchanger current (I(Na+/Ca2+)) across the left ventricular wall of rabbit and the relationship between I(Na+/Ca2+) and transmural depolarization heterogeneity.

Methods: By using whole-cell patch clamp techniques, action potentials (AP), I(Na+/Ca2+), and both rapid and slow components of delayed rectifier potassium current (I(Kr) and I(Ka)) were recorded in subendocardial (Endo), midmyocardial (M), and subepicardial (Epi) cells of the left ventricular wall of rabbit.

Results: AP duration in M cells was longer than that in Epi cells, P<0.01. At the test potential of +40 mV, outward I(Na+/Ca2+) in M cells was larger than that in Epi and Endo cells, P<0.01, P<0.05, respectively. At the test potential of -100 mV, inward I(Na+/Ca2+) in M cells was larger than that in Epi cells, P<0.05. At the test potential of +50 mV, the tail current density of I(Ka) in M cells was smaller than that in Epi cells, P<0.05, and there was no significant difference among the tail current densities of I(Kr) in Endo, M, and Epi cells.

Conclusion: The distribution of I(Na+/Ca2+) and I(Ka) across the left ventricular wall of rabbit is unequal, which contributes to the transmural depolarization heterogeneity.