Electrical impedance of cardiac muscle

I T HAS long been held that transmissionof excitation from cell to cell in cardiac muscle is effected by local-circuit current. Recent electron microscopy1"3 has shown that the myocardium is not a morphological syn-cytium; the intercalated discs are actually cell boundaries. If the resistances of the disc membranes are high, then local-circuit cur-rent transmission is unlikely, and the major possibility remaining would be that of chemi-cal junction transmission. Several lines of evi-dence have led to a questioning of the validity of the electrical theory of transmission.4"8 The present report deals with an effort to determine the resistance and the capacitance of the transverse membranes by measurement of tissue impedance in the direction of fiber orientation, before and after reduction of the interspace ion concentration. This work is an extension, with impedance measurements, of a previous report7 which presented D.C. re-sistance measurements. The passive current flow paths through a muscle strip may be lumped into two major parallel paths: (a) the path through the extracellular fluid (ecf), and (b) the path through the cell membranes and intracellular fluid (icf). The resistance of the extracellular path depends on the inter-space volume relative to the cell volume, and the resistance of the cellular path depends on the number and on the resistance of the cell membranes and on the myoplasmic resistance