Electric current flow in cell pairs isolated from adult rat hearts.

Cell pairs were isolated from ventricles of adult rat hearts so as to study cell‐to‐cell coupling. Both cells of each pair were impaled with micro‐electrodes connected to balanced bridge circuits. Rectangular current pulses were passed and the resulting voltage deflexions monitored. The data were analysed in terms of a delta configuration of three resistive elements, the resistances of the non‐junctional membrane of cell 1 and cell 2 (rm, 1 and rm, 2), and the resistance of the nexal membrane (rn). The nexal membrane resistance was found to be insensitive to voltage gradients across the non‐junctional membrane (range examined: ‐70 to ‐10 mV) and direction of current flow. The mean value of rn was 2.12 M omega ([K+]o = 12 mM). Taking into account morphological parameters, this corresponds to a specific nexal membrane resistance (Rn) of 0.1 omega cm2. Spontaneous uncoupling in which one cell remained polarized while the other one depolarized was never observed. The current‐voltage relationship of the non‐junctional membrane was found to be bell‐shaped. The specific resistance (Rm) at the resting membrane potential (approximately ‐50 mV) was 3.2 k omega cm2 ([K+]o = 12 mM). Comparative studies performed on single cells revealed a similar relationship Rm versus Vm. Rm at the resting membrane potential (Vm approximately ‐50 mV) was 2.5 k omega cm2 ([K+]o = 12 mM). The specific capacitance of the non‐junctional membrane (Cm) was determined from experiments on single cells. Cm was found to be independent of Vm (voltage range: ‐80 to 0 mV). The mean value of Cm was 1.66 microF/cm2 ([K+]o = 12 mM). For comparison, experiments on cell pairs and single cells were also carried out with [K+]o = 4 mM. The values obtained for Rn, Rm and Cm did not deviate significantly from those found with [K+]o = 12 mM.