Cl- permeability of sweat duct cell membranes: intracellular microelectrode analysis

Cl- permeability in the reabsorptive sweat duct (RSD) epithelium from normal subjects was studied using electrophysiological techniques. The average basolateral membrane potential (Vb) of normal ducts was -36.8 +/- 0.8 mV and the average apical membrane potential (Va) was -27.2 +/- 0.8 mV (n = 45). Amiloride in the lumen of microperfused sweat ducts hyperpolarized Va by 34.3 +/- 3.1 mV and Vb by 25.7 +/- 3.1 mV (n = 12) with a small but significant increase in voltage divider ratio (Ra/Rb) from 4.2 +/- 0.8 to 5.0 +/- 0.8 (n = 8). Cl- substitution in the lumen depolarized Va by +37 +/- 4.2 (n = 11) accompanied by a significantly larger increase in Ra/Rb from 4.8 +/- 2.6 (n = 8) to 7.0 +/- 3.1 (n = 8). Bath Cl- substitution depolarized Vb by +24.3 +/- 2.7 mV (n = 15) while decreasing Ra/Rb from 3.2 +/- 0.7 to 1.9 +/- 0.4 (n = 7). These results indicated a significant Cl- permeability in both apical and basolateral membranes. Removing Cl- from the lumen significantly decoupled Va and Vb and restricted the amiloride-induced hyperpolarization to the apical membrane. This result may suggest that intracellular Cl- might be responsible for coupling Va and Vb and that hyperpolarization of Va and Vb by amiloride may result in changes in intracellular Cl-. Alternatively, Va and Vb could be coupled through a Cl- sensitive paracellular shunt. These results are consistent with Cl- permeability in both apical and basolateral membranes of duct cells. However, the question of whether paracellular Cl- permeability is important in Cl- uptake cannot be determined from the present data.