Ion transport mechanisms in rat parotid intralobular striated ducts.
The intracellular pH (pHi) indicator 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein and microfluorimetry were used to characterize several ion transport mechanisms in rat parotid striated ducts. The recovery of ductal pHi from an acute acid load was Na+ dependent and inhibited by the amiloride analogue ethylisopropylamiloride with 50% inhibitory concentration 4.7 +/- 0.8 microM, indicating the presence of a Na(+)-H+ exchanger of the amiloride-insensitive type. The rate of this recovery was stimulated approximately 20% in ducts pretreated with the muscarinic agonist carbachol (10(-5) M) and inhibited approximately 20% in ducts pretreated with the beta-adrenergic agonist isoproterenol (10(-6) M). Upon removal of extracellular K+, ductal pHi rapidly decreased (0.19 +/- 0.02 pH units/min), consistent with a coupling between K+ and H+ (or OH-) fluxes in this tissue. In HCO(3-)-containing medium, the acidification due to K+ removal was blunted, arguing against ductal K(+)-HCO3- cotransport. However, the effect of K+ removal was inhibited by the K+ channel blocker Ba2+ (1 mM) and by the H+ channel blocker Zn2+ (25 microM), consistent with the involvement of electrically coupled K+ and H+ channels. The effect of K+ removal was unaffected by pretreatment of ducts with isoproterenol (10(-6) M) but markedly inhibited (approximately 50%) by pretreatment with carbachol (10(-5) M). No evidence for a significant component of Cl(-)-HCO3- exchange was found in striated ducts. The properties of the Na(+)-H+ exchanger and K(+)-H+ exchange mechanism identified here are consistent with their involvement in ductal salt reabsorption and secretion.
Clinical Investigations and Patient Care Branch, National Institute of Dental Research, National Institutes of Health, Bethesda, Maryland 20892.
M
M
Paulais
E J
EJ
Cragoe
R J
RJ
Turner
D000818:Animals; D017920:Antiporters / Q000378:metabolism; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism; D027963:Chloride-Bicarbonate Antiporters; D005470:Fluorometry; D007425:Intracellular Membranes / Q000378:metabolism; D007477:Ions; D010306:Parotid Gland / Q000378:metabolism*; D027961:Potassium-Hydrogen Antiporters; D051381:Rats; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism
D017920:Antiporters; D027963:Chloride-Bicarbonate Antiporters; D007477:Ions; D027961:Potassium-Hydrogen Antiporters; D017923:Sodium-Hydrogen Exchangers; D002118:Calcium