Direct current electrical measurement in epithelia: steady-state and transient analysis.

A method has been presented for the determination of resistance of biological tissues in which the PD response to step currents is determined. The delta PD after the dielectric capacitors are charged, divided by the current, gives the resistance, provided the current density is low enough so that the tissue behaves as a linear-bilateral system. In the gastric mucosa the PD continues to increase after the dielectric capacitors are charged and it is shown that this part of the delta PD is due to polarization of EMFs and should not be used in determining the resistance. It has been shown that (1) resistance measurements have enabled us to demonstrate that during acid secretion there is a neutral mechanism(s) for the movement of HCO3- out of and the entrance of Cl- into the oxyntic cells, (2) the transmucosal resistance varies inversely with the rate of acid secretion, and (3) the low resistance of the secreting frog fundus is due to the low resistance of the lumen-tubular cell pathway--the parallel pathways (the TIC or paracellular and surface cell pathways) have high resistances. The results of both the resistance and PD measurements have recently been analyzed with respect to the problem of whether the proton pump is neutral or electrogenic in the intact tissue.