Effect of methacholine on ionic permeability of basal membrane of the eccrine secretory cell

In an attempt to clarify the possible change in ionic permeability of the basal membrane of secretory cells during methacholine (MCH) stimulation, the effect of ionic substitution on membrane potential (PD) was studied in the isolated monkey palm eccrine secretory tubule. The mean PD (Vcb) was -73 mV. Stimulation with local iontophoresis of MCH caused a biphasic change in Vcb, an initial transient depolarization of 5 to 10 mV, followed by repolarization near the resting PD. MCH-induced PD transient reversed its polarity at -43 mV (MCH-null potential). Vcb markedly depolarized by an increase in [K+]b or a decrease in [Cl-]b. Ion-dependent partial potential ratio (Ti) using the estimated change in electromotive force delta Eb yielded values of 0.72 for K+ and 0.26 for Cl-, indicating that the basal membrane is conductive predominantly to K+ and Cl-. However, delta Vcb due to K+ or Cl- replacement did not change before or during MCH stimulation. Although replacement of Na+ with Tris+ or Li+ transiently depolarized Vcb, the delta Vcb reversed to hyperpolarization during MCH stimulation, suggesting that MCH causes a small increase in Na+ conductance across the basal membrane. The implication of these data have been discussed within the conceptual framework of ionic movements in Cl- transporting epithelia.