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 (EM), 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.
Intracellular Free Potassium, Sodium and Chloride Measured with Ion-Selective Microelectrodes from Salivary Gland Cells of the Snail Planorbis Corneus
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ANDREW BARBER; Intracellular Free Potassium, Sodium and Chloride Measured with Ion-Selective Microelectrodes from Salivary Gland Cells of the Snail Planorbis Corneus. J Exp Biol 1 March 1987; 128 (1): 349–369. doi: https://doi.org/10.1242/jeb.128.1.349
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