Dependence between intra- and extracellular action potentials of isolated frog muscle fibres at different temperatures.

The intra- and extracellular action potentials of isolated frog muscle fibre immersed in a volume conductor at different temperatures are described. It was found that upon increasing the temperature the amplitude of the first time derivative of the intracellular action potentials increased linearly, whereas the amplitude of the second time derivative increased nonlinearly. The duration of the separate phases of the time derivatives shortened upon heating, as the velocity of spreading of the excitation increased. The length of the separate phases of the space derivatives of the action potential shortened when increasing the temperature. The amplitudes of the space derivatives were calculated. The changes in the derivatives of the action potential were explained by the influence of the temperature on the peak inward and outward transmembrane current. The changes in the extracellular action potentials produced by the temperature near the membrane and at longer radial distance at points far and near the end of the fibre are described. They were explained by the changes in the space derivatives of the intracellular action potential as well as by the features of the distribution of the extracellular potential field in the volume conductor around the finite-in-length excitable fibre.