title: Membrane potential modulates divalent cation entry in rat parotid acini.
abstract: This study examines the effect of membrane potential on divalent cation entry in dispersed parotid acini following stimulation by the muscarinic agonist, carbachol, and during refill of the agonist-sensitive internal Ca2+ pool. Depolarizing conditions (addition of gramicidin to cells in Na(+)-containing medium or incubation of cells in medium with elevated [K+]) prevent carbachol-stimulated hyperpolarization of acini and also inhibit carbachol activation of Ca2+ and Mn2+ entry into these cells. Conditions promoting hyperpolarization (cells in medium with Na+ or with N-methyl-D-glucamine instead of Na+) enhance carbachol stimulation of divalent cation entry. Intracellular Ca2+ release (initial increase in [Ca2+]i) does not appear to be affected by these manipulations. Mn2+ entry into resting and internal Ca2+ pool-depleted cells (10-min carbachol stimulation in a Ca(2+)-free medium) is similarly affected by membrane potential modulations, and refill of the internal pool by Ca2+ is inhibited by depolarization. The inhibitory effects of depolarization on divalent cation entry can be overcome by increasing extracellular [Ca2+] or [Mn2+]. These data demonstrate that the modulation of Ca2+ entry into parotid acini by membrane potential is most likely due to effects on the electrochemical gradient (Em-ECa) for Ca2+ entry.
authors.affiliation: Clinical Investigations and Patient Care Branch, National Institute of Dental Research, National Institutes of Health, Bethesda, Maryland 20892.
authors.forename: L M
authors.initials: LM
authors.lastname: Mertz
authors.forename: B J
authors.initials: BJ
authors.lastname: Baum
authors.forename: I S
authors.initials: IS
authors.lastname: Ambudkar
mesh_terms: D000818:Animals; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism; D002217:Carbachol / Q000494:pharmacology; D002412:Cations / Q000378:metabolism*; D066298:In Vitro Techniques; D008297:Male; D008345:Manganese / Q000378:metabolism; D008564:Membrane Potentials; D010306:Parotid Gland / Q000378:metabolism / Q000502:physiology*; D011188:Potassium / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D002412:Cations; D008345:Manganese; D002217:Carbachol; D011188:Potassium; D002118:Calcium