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Journal of Experimental Biology 128,349-369 (1987)
Published by Company of Biologists 1987

Intracellular Free Potassium, Sodium and Chloride Measured with Ion-Selective Microelectrodes from Salivary Gland Cells of the Snail Planorbis Corneus

ANDREW BARBER ¹

¹ Physiological Institute, University of Munich, Pettenkoferstrasse 12, 8000 Munich 2, West Germany; Abteilung Pharmakologie, E. Merck AG, Frankfurter Strasse 250, 6100 Darmstadt 1, West Germany

Double-barrelled, ion-selective microelectrodes (ISMEs) have been used to measure the intracellular free concentrations of K⁺ ([K⁺]₁,), Na⁺ ([Na⁺]_i) and Cl^- ([Cl^-]₁), together with membrane potentials (E_M), from single salivary gland acinar cells of the pond snail Planorbis corneus. After adjustments had been made for the cross-sensitivities of the ion-exchangers to other intracellular ions, the mean concentrations were estimated to be: [K⁺]₁, 42.9 mmoll^-1; [Na⁺]₁, 2.4 mmoll^-; and [Cl^-]_i, 10.3 mmoll^-. The mean Nernstian equilibrium potentials for K⁺, Na⁺ and Cl^- were calculated to be -88 mV, +74.4 mV and -41 mV, respectively. The basolateral membrane of Planorbis salivary cells appears to be permeable to K⁺ and Na⁺ under resting conditions, because blocking the electrogenic Na⁺/K⁺ pump with K⁺ -free saline or ouabain revealed the presence of a large passive efflux of K⁺ and an influx of Na⁺. Salivary gland cells also lose intracellular Cl^- rapidly in Cl^-free saline (extracellular Cl^- replaced by sulphate) which, along with other evidence, indicates a substantial resting permeability of the salivary cell membrane to Cl^-. Stimulating gland cells with 10^-4 moll^-1 acetylcholine (ACh) led to a depolarization of EM, a rise in [Na⁺]₁, and a fall in [K⁺]₁. This was followed by a transient hyperpolarization of EM and a recovery of [Na⁺]₁, and [K⁺]₁, to their original levels. There was no evidence that [Cl^-]₁, changes after stimulation with ACh. The mechanism of action of ACh on Planorbis salivary gland cells and its relevance for secretion are discussed.

Key words: salivary gland cells, intracellular K⁺, intracellular Na⁺, intracellular Cl^-, ion-selective microelectrodes, Planorbis corneus, acetylcholine

Accepted on November 10, 1986