The electrical constants of Purkinje fibres

The aim of the present work was to measure the myoplasm resistance and the membrane resistance and capacity in Purkinje fibres of the mammalian heart. A knowledge of these characteristics is important in any discussion of cardiac excitation and conduction, and may also be of interest to those concerned with the movement of ions through cell membranes. The theoretical method employed was similar in principle to that introduced by Hodgkin & Rushton (1946). This is based on the assumption that a single fibre can be regarded as a cable-like structure with a core of well-conducting protoplasm and a thin surface membrane having a high resistance and a large capacity per unit area. In the present case the analysis was simplified by keeping the fibre in a large volume of saline and using internal electrodes to apply current and to record potential. This has the advantage that fewer independent measurements are needed in order to determine the basic constants of the fibre. The equations of cable theory are usually applied to a uniform fibre of infinite length, while the fibres of the cardiac syncytium fuse with one another at distances of less than 1 mm. The difficulties arising from this situation were reduced by using single fibres in the Purkinje system of the kid which were found to be free from interconnexions for a length of a few mm and by making use of a phenomenon characteristic for heart muscle, the 'healing-over' of cut surfaces. THEORY