Na(+)-H+ exchange in sheep parotid endpieces. Apparent insensitivity to amiloride.
We have used microspectrofluorimetry with the pH-sensitive dye, BCECF, to examine the control of intracellular pH in the secretory endpieces of the sheep parotid gland. Unstimulated endpieces in HCO3(-)-free media have a cytosolic pH of 7.5 +/- 0.03 (n = 69) which is maintained by a Na(+)-dependent proton extrusion process that can be partially supported by Li+ but not by Cs+, and is not affected by changes in extracellular Cl-, HCO3- or K+. It is not blocked by SITS or DIDS, which inhibit Na(+)-(n)HCO3- co-transport and CL(-)-HCO3- exchange, nor is it sensitive to the amiloride analogs, MIA and EIPA, which inhibit Na(+)-H+ exchangers, although very high concentrations of amiloride itself (1 mmol/l) have a (probably non-specific) inhibitory effect. It seems likely that sheep parotid secretory endpieces do contain a Na(+)-H+ exchanger that drives secretion of a HCO3(-)-rich juice, and that its insensitivity to amiloride and its analogs explains why these drugs do not block fluid secretion by the intact sheep parotid gland.
Poronnik
P
P
Department of Physiology, University of Sydney, NSW, Australia.
Young
J A
JA
Cook
D I
DI
D000584:Amiloride / Q000494:pharmacology*; D000818:Animals; D001572:Benzofurans; D001692:Biological Transport / Q000187:drug effects; D004988:Ethers, Cyclic; D005452:Fluoresceins; D005456:Fluorescent Dyes; D006859:Hydrogen / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D010306:Parotid Gland / Q000187:drug effects / Q000378:metabolism*; D012756:Sheep; D012964:Sodium / Q000378:metabolism*
D001572:Benzofurans; D004988:Ethers, Cyclic; D005452:Fluoresceins; D005456:Fluorescent Dyes; C061665:sodium-binding benzofuran isophthalate; D000584:Amiloride; D006859:Hydrogen; C043829:2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein; D012964:Sodium