Related Experiment Videos
Secretagogue-induced 86Rb+ efflux from bovine parotid is HCO3- dependent
1Clinical Investigations and Patient Care Branch, National Institute of Dental Research, National Institutes of Health, Bethesda, Maryland 20892.
Abstract:
Muscarinic agonist (carbachol)-induced K+ loss from a bovine parotid mince was studied using 86Rb+ as a K+ marker. In contrast to our previous studies with the rat parotid [Am. J. Physiol. 261 (Gastrointest. Liver Physiol. 24): G111-G118, 1991] in which both Cl(-)-dependent and HCO3(-)-dependent components of carbachol-induced 86Rb+ efflux were observed, no significant evidence for Cl(-)-dependent 86Rb+ loss was detected in the bovine parotid. HCO3(-)-dependent agonist-induced 86Rb+ loss was blunted by K+ and Cl- channel blockers and by removal of extracellular Ca2+, consistent with the hypothesis that this 86Rb+ loss occurs via a Ca(2+)-activated K+ channel and that this cation loss serves to electrically balance the concomitant loss of HCO3- via an electrically conductive pathway, presumably an apical anion channel. Acetate, formate, and propionate could substitute for HCO3-. Interpreted in terms of current models of salivary fluid secretion, which hypothesize that the production of fluid is secondary to anion secretion accompanied by an electrically coupled K+ loss, these results indicate that salivary production in the bovine parotid is driven almost exclusively by acinar HCO3- secretion.
Insights
Bovine parotid glands secrete fluid primarily through bicarbonate secretion, unlike rat parotid glands. This study used 86Rubidium to track potassium loss, revealing a calcium-activated potassium channel mechanism essential for this bicarbonate-driven salivary production.
Area of Science:
- Physiology
- Biochemistry
- Cell Biology
Background:
- Salivary fluid secretion is a complex process involving ion transport.
- Previous studies in rat parotid glands identified both chloride and bicarbonate-dependent components in agonist-induced ion loss.
Purpose of the Study:
- To investigate the ion transport mechanisms responsible for muscarinic agonist-induced potassium loss in bovine parotid glands.
- To compare these mechanisms with those previously observed in rat parotid glands.
Main Methods:
- Utilized 86Rubidium (86Rb+) as a marker for potassium (K+) efflux from bovine parotid mince.
- Administered muscarinic agonist carbachol to stimulate ion loss.
- Employed K+ and Cl- channel blockers and manipulated extracellular Ca2+ concentrations.
Main Results:
- No significant evidence of chloride-dependent 86Rb+ loss was detected in bovine parotid glands.
- Bicarbonate-dependent 86Rb+ loss was observed and was sensitive to K+ and Cl- channel blockers.
- This bicarbonate-dependent K+ loss was blunted by the removal of extracellular Ca2+.
- Acetate, formate, and propionate could substitute for bicarbonate, suggesting a role for permeable anions.
Conclusions:
- Bovine parotid salivary production is driven almost exclusively by acinar bicarbonate secretion.
- The observed K+ loss occurs via a Ca2+-activated K+ channel, electrically balancing the bicarbonate efflux through an apical anion channel.
- This mechanism differs from the rat parotid, highlighting species-specific differences in salivary secretion pathways.