Electrical resistance of a capillary endothelium.

Abstract

The electrical resistance of consecutive segments of capillaries was determined by a method in which the microvessels were treated as a leaky, infinite cable. A 2-dimensional analytical model to describe the potential field in response to intracapillary current injection was formulated. The model allowed determination of the electrical resistance from 4 sets of data: the capillary radius, the capillary length constant, the length constant in the mesentery perpendicular to the capillary and the relative potential drop across the capillary wall. Of particular importance were the mesothelial membranes covering the mesenteric capillaries with resistances several times higher than that of the capillary endothelium. Frog mesenteric capillaries [27] were characterized. The average resistance of the endothelium was 1.85 .OMEGA.cm2, which compares well with earlier determinations of the ionic permeability of such capillaries. Heterogeneity with respect to resistance was observed, that of 10 arterial capillaries being 3.0 .OMEGA.cm2 as compared with 0.95 .OMEGA.cm2 for 17 mid and venous capillaries. The average in situ length constant was 99 .mu.m for the arterial capillaries and 57 .mu.m for the mid and venous capillaries. The ions that carry the current must move paracellularly, through junctions that are leaky to small solutes.