Influence of intracellular potential and conduction velocity on extracellular muscle fibre potential.

The influence of alterations in intracellular action potential (ICAP) duration and in muscle fibre conduction velocity (CV) on the extracellular action potential (ECAP) duration was studied. The experiments were carried out on frog isolated skeletal muscle fibres. The ECAPs were recorded at different radial distances (from 0 μm to 3000 μm) to the muscle fibre membrane. Alterations in the CV were induced by changes in the temperature of the medium. The CV decrease led to increase in both ICAP duration and duration of the ECAPs recorded at different radial distances. The ECAP duration reflected changes in the ICAP duration and increased together with increase in the radial distances. The different extent of alteration in ICAP duration and CV following potassium conductivity blockage was used as a model for separately studying the effects of these two parameters on the ECAP duration. The duration of the ECAP in the vicinity of the fibre reflected changes in the ICAP rising time (Rt), and were practically independent of alterations of the CV. The ECAP duration at large radial distance depended on CV alterations and on radial distance.