Abstract
Current density, the membrane current value divided by membrane capacitance (C(m)), is widely used in cellular electrophysiology. Comparing current densities obtained in different cell populations assume that C(m) and ion current magnitudes are linearly related, however data is scarce about this in cardiomyocytes. Therefore, we statistically analyzed the distributions, and the relationship between parameters of canine cardiac ion currents and C(m), and tested if dividing original parameters with C(m) had any effect. Under conventional voltage clamp conditions, correlations were high for I(K1), moderate for I(Kr) and I(Ca,L), while negligible for I(Ks). Correlation between I(to1) peak amplitude and C(m) was negligible when analyzing all cells together, however, the analysis showed high correlations when cells of subepicardial, subendocardial or midmyocardial origin were analyzed separately. In action potential voltage clamp experiments I(K1,) I(Kr) and I(Ca,L) parameters showed high correlations with C(m). For I(NCX), I(Na,late) and I(Ks) there were low-to-moderate correlations between C(m) and these current parameters. Dividing the original current parameters with C(m) reduced both the coefficient of variation, and the deviation from normal distribution. The level of correlation between ion currents and C(m) varies depending on the ion current studied. This must be considered when evaluating ion current densities in cardiac cells.