Ionic dependence of the resting membrane potential of rabbit lacrimal gland in vitro

Abstract

1. 1. Intracellular measurements of membrane potentials were made from acinar cells of rabbit lacrimal gland in vitro at 25 ± 0.03° C (± S.E.) by using 3 M KCl-filled glass microelectrodes. 2. 2. The mean resting membrane potential in a Krebs-Ringer bicarbonate solution was -26.7 ± 0.3 mV, insidethe cell negative. 3. 3. Elevation of the external K + concentration ([K + ] 0 ) caused depolarization of the resting potential. When [K + ] 0 was above 5 mM, a tenfold increase in [K + ] 0 decreased the membrane potential by approx. 15 mV. This depolarization was not mediated by the release of acetylcholine (ACh) from the depolarized nerve terminals since it was seen in the presence of 10 -5 M atropine. 4. 4. Equimolar replacement of [Na + ] 0 by either choline or Tris at constant [K + ] 0 (5.8 mM) produced hyperpolarization. The resting potential was -33.1 ± 0.6 mV and -38.9 ± 0.6 mV, when 70 mM [Na + ] 0 was replaced by choline and Tris respectively. 5. 5. The resting potential was not affected by either partial or complete substitution of [Cl - ] 0 with SP 4 2- . 6. 6. Omission of Ca 2+ from the external medium in the absence and in the presence of 5 mM EGTA decreased the membrane potential by 5.4 mV and 11.8 mV respectively. 7. 7. It is concluded that the resting membrane potential of rabbit lacrimal gland is independent of the external Cl - but it primarily depends on the external Na + , K + and Ca 2+ . The data were interpreted in terms of high membrane permeability to Na + and K + of the lacrimal gland cells. The relative permeability ratio, P Na /P K , in normal Krebs-Ringer bicarbonate solution was estimated to be 0.35. © 1977.