Voltage clamp simulations for multifiber bundles in a double sucrose gap: radial vs. longitudinal resistance effects.

Voltage clamp responses of a single excitable fiber were simulated using a core conductor model including a high external resistance (Rs) in series to the fiber membrane to allow for intercellular clefts in a multifiber preparation. In terms of specific resistance, Rs was between 68 and 264 omega cm2. Internal resistivity (Ri) was taken to be zero or 200 omega cm. The aim of the study was to quantify the expected antagonistic effects of external and internal resistances on Na current measurements. With Ri = 0, the external resistance was found to cause a strong depression of fast inward current compared to an ideal space clamp at command potentials between -30 and 30 mV. With Ri = 200 omega cm, the depression of inward current was partially removed. The effects of Rs and Ri on membrane current measurement were illustrated by cable analysis assuming a quasi-steady state of the fiber at peak time of inward current.