Acetylcholine-Induced Na+ influx in the mouse lacrimal gland acinar cells: Demonstration of multiple Na+ transport mechanisms by intracellular Na+ activity measurements
- 1 June 1987
- journal article
- research article
- Published by Springer Nature in The Journal of Membrane Biology
- Vol. 98 (2), 135-144
- https://doi.org/10.1007/bf01872126
Abstract
In the isolated, superfused mouse lacrimal gland, intracellular Na+ activities (aNa i ) of the acinar cells were directly measured with double-barreled Na+-selective microelectrodes. In the nonstimulated conditionaNa i was 6.5±0.5 mM and membrane potential (V m ) was −38.9±0.4 mV. Addition of 1 mM ouabain or superfusion with a K+-free solution slightly depolarized the membrane and caused a gradual increase inaNa i . Stimulation with acetylcholine (ACh, 1 μM) caused a membrane hyperpolarization by about 20 mV and an increase inaNa i by about 9 mM in 5 min. The presence of amiloride (0.1 mM) reduced the ACh-induced increase inaNa i by approximately 50%, without affectingV m and input resistance in both nonstimulated and ACh-stimulated conditions. Acid loading the acinar cells by an addition/withdrawal of 20 mM NH4Cl or by replacement of Tris+-buffer saline solution with HCO 3 − /CO2-buffered solution increasedaNa i by a few mM. Superfusion with a Cl−-free NO 3 − solution or 1 mM furosemide or 0.5 mM bumetanide-containing solution had little effect on the restingaNa i levels, however, it reduced the ACh-induced increase inaNa i by about 30%. Elimination of metabolite anions (glutamate, fumarate and pyruvate) from the superfusate reduced both the restingaNa i and the ACh-induced increase inaNa i . The present results suggest the presence of multiple Na+ entry mechanisms activated by ACh, namely, Na+/H+ exchange, Na-K-Cl cotransport and organic substrate-coupled Na+ transport mechanisms.Keywords
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