Mechanism of secretagogue-induced HCO3- and Cl- loss from rat parotid acini.
The Cl(-)- and HCO3(-)-dependent components of muscarinic agonist (carbachol)-induced K+ loss from a rat parotid mince were studied using 86Rb+ as a K+ marker. Both components of 86Rb+ loss were blunted by K+ and Cl- channel blockers and by removal of extracellular Ca2+, consistent with the hypothesis that 86Rb+ loss occurs via a Ca(2+)-activated K+ channel and that this cation loss serves to electrically balance a concomitant loss of the corresponding anion via one or more conductive pathways (channels). Two tissue "pools" of 86Rb+ were observed, a carbachol-sensitive pool and a carbachol-insensitive pool (approximately 70 and approximately 30% of the total 86Rb+ content, respectively). There was no evidence for a time-dependent desensitization of the muscarinic response of the carbachol-sensitive pool. Cl(-)-dependent 86Rb+ loss was not affected by HCO3- addition, suggesting that both Cl- and HCO3- secretion are accompanied by 86Rb+ loss from the same pool and thus occur from the same cells. HCO3(-)-dependent 86Rb+ loss was not enhanced by lowering the extracellular Na+ concentration, indicating that the HCO3- exit pathway is not a Na(+)-HCO3- symport. The data are consistent with the postulate that Cl- and HCO3- are secreted by rat parotid acinar cells via the same or very similar conductive transport pathways in response to muscarinic stimulation.
Lee
S I
SI
Clinical Investigations and Patient Care Branch, National Institute of Dental Research, National Institutes of Health, Bethesda, Maryland 20892.
Turner
R J
RJ
D000818:Animals; D001639:Bicarbonates / Q000378:metabolism*; D002217:Carbachol / Q000494:pharmacology*; D002712:Chlorides / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D010306:Parotid Gland / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D012044:Regression Analysis; D012414:Rubidium Radioisotopes; D012964:Sodium / Q000502:physiology; D013373:Substance P / Q000494:pharmacology; D062367:ortho-Aminobenzoates / Q000494:pharmacology
D001639:Bicarbonates; D002712:Chlorides; D012414:Rubidium Radioisotopes; D062367:ortho-Aminobenzoates; D013373:Substance P; D002217:Carbachol; C001209:fenamic acid; D012964:Sodium