Modulation of ATP-dependent Ca2+ transport in rat parotid basolateral membrane vesicles by K+ + Cl- flux.
In basolateral membrane vesicles (BLMV) isolated from rat parotid glands, the initial rate of ATP-dependent Ca2+ transport, in the presence of KCl, was approx. 2-fold higher than that obtained with mannitol, sucrose or N-methyl-D-glucamine (NMDG)-gluconate. Only NH4+, Rb+, or Br- could effectively substitute for K+ or Cl-, respectively. This KCl activation was concentration dependent, with maximal response by 50 mM KCl. An inwardly directed KCl gradient up to 50 mM KCl had no effect on Ca2+ transport, while equilibration of the vesicles with KCl (greater than 100 mM) increased transport 15-20%. In presence of Cl-, 86Rb+ uptake was 2.5-fold greater than in the presence of gluconate. 0.5 mM furosemide inhibited 86Rb+ flux by approx. 60% in a Cl- medium and by approx. 20% in a gluconate medium. Furosemide also inhibited KCl activation of Ca2+ transport with half maximal inhibition either at 0.4 mM or 0.05 mM, depending on whether 45Ca2+ transport was measured with KCl (150 mM) equilibrium or KCl (150 mM) gradient. In a mannitol containing assay medium, potassium gluconate loaded vesicles had a higher (approx. 25%) rate of Ca2+ transport than mannitol loaded vesicles. Addition of valinomycin (5 microM) to potassium gluconate loaded vesicles further stimulated (approx. 30%) the Ca2+ transport rate. These results suggest that during ATP dependent Ca2+ transport in parotid BLMV, K+ can be recycled by the concerted activities of a K+ and Cl- coupled flux and a K+ conductance.
Ambudkar
I S
IS
Clinical Investigations and Patient Care Branch, National Institute of Dental Research, Bethesda, MD 20892.
Baum
B J
BJ
D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D000838:Anions; D001693:Biological Transport, Active / Q000187:drug effects; D001966:Bromine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002132:Calcium Radioisotopes; D002412:Cations; D002462:Cell Membrane / Q000378:metabolism; D002712:Chlorides / Q000494:pharmacology*; D004553:Electric Conductivity; D005665:Furosemide / Q000494:pharmacology; D007700:Kinetics; D008297:Male; D010306:Parotid Gland / Q000378:metabolism*; D011188:Potassium / Q000494:pharmacology*; D011189:Potassium Chloride / Q000494:pharmacology; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D012413:Rubidium / Q000494:pharmacology; D012414:Rubidium Radioisotopes
D000838:Anions; D002132:Calcium Radioisotopes; D002412:Cations; D002712:Chlorides; D000644:Quaternary Ammonium Compounds; D012414:Rubidium Radioisotopes; D011189:Potassium Chloride; D005665:Furosemide; D000255:Adenosine Triphosphate; D012413:Rubidium; D011188:Potassium; D001966:Bromine; D002118:Calcium