Muscarinic regulation of potassium transport in a human submandibular epithelial cell line
Ship, J.A.; Patton, L.L.; Wellner, R.B.
American Journal of Physiology 259(2 Pt 1): C340-C348
1990
ISSN/ISBN: 0002-9513 PMID: 2116725 Document Number: 367275
Results of previous studies suggest that the transport of K+ by salivary ducts is under muscarinic control. The mechanisms by which this regulation occurs have not been well defined, however. In this paper, we describe mechanisms involved in the muscarinic regulation of K+ (86Rb) transport in HSG-PA, an epithelial cell line derived from human submandibular gland duct. Stimulation of HSG-PA cells by carbachol, a muscarinic agonist, increases both 86Rb influx and efflux, which results in a decrease in the equilibrium content of 86Rb within the cells. Increases in both fluxes are dose dependent with respect to carbachol concentration, and both responses can be blocked by atropine, a muscarinic antagonist. The carbachol-stimulated 86Rb fluxes appear to be calcium dependent since 1) the calcium ionophore A23187 increases 86Rb fluxes in these cells, 2) cells loaded with 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA; a calcium chelator) exhibit a reduced ability to respond to carbachol stimulation, and 3) removal of extracellular calcium concentration reduces the carbachol-stimulated effects. Treatment of HSG-PA cells with 10-7 M phorbol myristate acetate (PMA) partially blocks the carbachol-stimulated changes in 86Rb fluxes, suggesting that protein kinase C plays a role in this response. PMA also partially blocks A23187-stimulated 86Rb influx, suggesting that activation of protein kinase C inhibits muscarinic-stimulated K+ influx by blocking either the Ca2+ signal (X. He, X. Wu, and B. J. Baum. Biochem. Biophys. Res. Commun. 152: 1062-1069, 1988), steps subsequent to this effect, or both. Neither carbachol-stimulated 86Rb flux is inhibited by ouabain (a Na+-K+-ATPase inhibitor) or bumetanide (a Na+-K+-2Cl- cotransport inhibitor), but both stimulated fluxes are inhibited by the K+ channel blockers quinine, tetraethylammonium chloride (TEA), and scorpion venom containing charybodotoxin. TEA blocks a substantial portion of the carbachol-induced calcium signal, however, which probably accounts for the fact that TEA concentrations, which effectively block-carbachol-stimulated 86Rb fluxes, are ineffective in blocking A23187-stimulated 86Rb fluxes. In contrast, quinine and scorpion venon effectively inhibit both carbachol- and A23187-stimulated 86Rb fluxes, suggesting that muscarinic regulation of K+ fluxes involves the participation of one or more classes of Ca2+-regulated K+ channels.