Unstirred-layer model for the long time-constant transient voltage response to current in epithelial tissue

Abstract

In previous work on the in vitro frog gastric mucosa it was found that step currents produced a transmucosal voltage response of about 100 seconds duration. The voltage response can be formally represented by five resistors in series, with four of the resistors shunted by dielectric capacitors. It was shown that the two resistance-capacitor subcircuits with the longest time constants demand capacitors of the order of Farads cm −2 and that this portion of the transient can be explained on the basis of mechanisms involving the polarization of e.m.f.'s. In the present paper a conceptual unstirred-layer model is presented in which the transient voltage response to step currents is comparable to the observed response in the gastric mucosa. In both the model and in the gastric mucosa the voltage response for small currents is linear and bilateral and deviates from linear bilateral behavior at higher current densities. The implication of the unstirred-layer model is discussed in relation to other models previously proposed as explanations for the long-time constant transient.