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Bicarbonate transport in sheep parotid secretory cells.
Author(s) -
Steward M C,
Poronnik P,
Cook D I
Publication year - 1996
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1996.sp021535
Subject(s) - chemistry , stimulation , bicarbonate , amiloride , intracellular ph , niflumic acid , efflux , acetylcholine , channel blocker , intracellular , biophysics , biochemistry , pharmacology , endocrinology , sodium , calcium , biology , organic chemistry
1. Intracellular pH (pH1) was measured by microfluorimetry in secretory endpieces isolated from sheep parotid glands and loaded with the pH‐sensitive fluoroprobe 2', 7'‐bis(2‐carboxyethyl)‐5(6)‐carboxyfluorescein (BCECF). 2. Stimulation with 1 microM acetylcholine (ACh) caused a large, transient decrease in pH1 of 0.37 +/‐ 0.02 pH units followed by a slower recovery. The transient, which was reduced by 60% in the absence of HCO3‐, could be attributed mainly to HCO3‐ efflux. During sustained stimulation, pH1 increased to a value that exceeded the resting value by 0.083 +/‐ 0.023 pH units after 20 min. 3. The anion channel blocker NPPB (0.1 mM) reduced the transient acidification in response to ACh by 48% and raised pH1 during sustained stimulation. Simultaneous application of NPPB and ACh accelerated the re‐alkalinization following the initial acidification, indicating that NPPB inhibits HCO3‐ efflux. 4. The stilbene derivative H2DIDS (0.5 mM) reduced the transient acidification in response to ACh by 76% but caused a marked decrease in pH1 during sustained stimulation. Simultaneous application of H2DIDS and ACh slowed the re‐alkalinization following the initial acidification, indicating that the main effect of H2DIDS was to inhibit HCO3‐ accumulation. 5. In the absence of HCO3‐, the recovery from an acid load was unaffected by ACh stimulation. Acid extrusion, although dependent on Na+, was not inhibited by amiloride (1 mM), clonidine (1 mM) or H2DIDS (0.5 mM) and was therefore provisionally attributed to a Na(+)‐H+ exchanger isoform other than NHE1 or NHE2. 6. In the presence of HCO3‐, the rate of recovery from an acid load was reduced during ACh stimulation, probably as a result of the increased efflux of HCO3‐. Acid extrusion was dependent on Na+ and was significantly inhibited by H2DIDS. 7. We conclude that ACh‐evoked HCO3‐ secretion in the sheep parotid gland differs from that in many other salivary glands by being driven predominantly by basolateral Na(+)‐HCO3‐ cotransport rather than by Na(+)‐H+ exchange.