title: Involvement of carboxyl groups in the divalent cation permeability of rat parotid gland basolateral plasma membrane.
abstract: Divalent cation permeability of rat parotid gland basolateral plasma membranes was examined in dispersed parotid acini (by Ca2+ or Mn2+ entry) and in isolated basolateral plasma membrane vesicles (BLMV, by 45Ca2+ influx). Mn2+ entry (fura2 quenching) was about 1.6 fold higher in internal Ca2+ pool-depleted acini (Ca(2+)-depl acini) than in unstimulated cells. Mn2+ entry into Ca(2+)-depl acini was increased at external pH > 7.4 and decreased at pH < 7.4. Pretreatment of Ca(2+)-depl acini with the relatively hydrophobic carboxylic group reagent, N,N'-dicyclohexylcarbodiimide (DCCD, 50 microM for 30 min) resulted in the inhibition of Mn2+ entry into Ca(2+)-depl acini to unstimulated levels. Another hydrophobic carboxyl group reagent, N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ) and the relatively hydrophilic carboxyl group reagents, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) and 1-cyclohexyl-3-(2-morpholinoethyl)carbodiimide (CMCD) did not affect Mn2+ entry. Similar to the effects in intact acini, Ca2+ influx into BLMV was decreased when the external pH was lowered below 7.4. Also DCCD (5 mM, 30 min), but not EEDQ, decreased (40%) Ca2+ influx in BLMV. However, unlike in acini, the hydrophilic reagents, EDC, EAC, and CMCD decreased Ca2+ permeability in BLMV and the effects were nonadditive with the decrease induced by DCCD. The aggregate effects of carboxyl group reagents on the Ca2+ and Mn2+ permeability in BLMV and intact acini, respectively, suggest that a critical carboxyl group (most likely accessible from the cytoplasmic side of the plasma membrane) is involved in divalent cation flux in rat parotid acinar cells.
authors.affiliation: Clinical Investigations and Patient Care Branch, National Institute of Dental Research, National Institutes of Health, Bethesda, Maryland 20892.
authors.forename: T
authors.initials: T
authors.lastname: Lockwich
authors.forename: L M
authors.initials: LM
authors.lastname: Mertz
authors.forename: I S
authors.initials: IS
authors.lastname: Ambudkar
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D002413:Cations, Divalent / Q000378:metabolism*; D002463:Cell Membrane Permeability / Q000502:physiology; D002478:Cells, Cultured; D004024:Dicyclohexylcarbodiimide / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D008297:Male; D008345:Manganese / Q000378:metabolism; D010306:Parotid Gland / Q000166:cytology / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D017208:Rats, Wistar
chemical_list: D002413:Cations, Divalent; D008345:Manganese; D004024:Dicyclohexylcarbodiimide; D002118:Calcium