Relationship between ion currents and membrane capacitance in canine ventricular myocytes

Abstract Current density, the membrane current value divided by membrane capacitance (Cm), is widely used in cellular electrophysiology. This assumes that Cmand ion current magnitudes are linearly related, however there is no data about this in cardiac muscle. Therefore, we statistically analysed parameters of cardiac ion currents and Cm, and tested if dividing original parameters with Cmhad any effect. Relationship between the measured parameters and Cmwas tested with correlation analysis. Under CVC conditions, correlations were high for IK1, moderate for IKrand ICa,L, while negligible for IKs. In case of Ito1, correlation between peak amplitude and Cmwas negligible when analysing all cells together, however, the analysis showed high correlations when cells of subepicardial, subendocardial or midmyocardial origin were analysed separately. In APVC experiments IK1,IKrand ICa,Lparameters showed high correlations with Cm. For INCX, INa,lateand IKsthere were low-to-moderate correlations between Cmand these current parameters. Dividing the original current parameters with Cmeither “normalised” the originally non-normal distributions or reduced the effect size of non-normality. Furthermore, dividing with Cmshowed a tendency to reduce coefficient of variance, reaching statistical significance in some cases.