Intracellular pH in the rat mandibular salivary gland: the role of Na−H and Cl−HCO₃ antiports in secretion

Abstract

Intracellular pH (pH_i) in the perfused rat mandibular gland was determined from the distribution of DMO (5,5-dimethyl-2,4-oxazolidinedione). In unstimulated glands, pH_i averaged 7.12±0.02. Stimulation with a “standard” (submaximal) concentration (0.3 μmol/l) of acetylcholine (ACh) caused a fall in pH_i to 6.81±0.06 over 60 min, but a maximal concentration (1.0 μmol/l) caused an initial rise in pH_i to 7.60±0.02, followed by a fall to 7.45±0.02 over 60 min. After replacement of perfusate Cl with gluconate, the standard ACh concentration caused a rise in pH_i to 7.50±0.02 followed by a fall to 7.27±0.04 after 60 min, concomitant with a 76% fall in secretory rate and a rise in salivary HCO₃ concentration from 14±0.9 to 67±1.5 mmol/l. Furosemide (1 mmol/l) had a similar effect to gluconate replacement except that secretory rate fell only by 60%. Bumetanide (1 mmol/l), which inhibited secretion by 67%, did not cause pH_i to rise following ACh stimulation but prevented the fall seen with ACh alone. Acetazolamide and methazolamide (1 mmol/l) had no effect on the salivary secretory response to ACh but they caused pH_i to rise, respectively, to 7.20±0.03 and 7.43±0.02. Bumetanide and methazolamide together caused pH_i to rise to 7.58±0.02 and reduced the secretory response to ACh by 91%. The disulfonic stilbene, SITS, caused pH_i to rise to 7.26±0.03. Ouabain and amiloride both caused resting pH_i to fall closer to equilibrium and largely abolished the gland's responsiveness to ACh. The results suggest that rat mandibular secretion depends both on a Na−K−2Cl symport and on Na−H and Cl−HCO₃ antiports present in the basolateral membranes of the secretory cells in proportions of about 8 (Na−K−2Cl symport) to 5 (Na−H antiport) to 3 (Cl−HCO₃ antiport).