Modulation of Na(+)‐H+ exchange by altered cell volume in perfused rat mandibular salivary gland.

Abstract

Manchester M13 9PT, UK 1. Intracellular pH (pH1) was measured by spectrofluorometry in perfused mandibular salivary glands isolated from the rat and loaded with the pH-sensitive fluoroprobe 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF). Cell volume changes were estimated from changes in intracellular water content measured by proton NMR spectroscopy.2. Stimulation with 1 ,UM acetylcholine (ACh) led to a 15 + 2% decrease in cell volume. A transient decrease in pH1 was followed by a sustained increase (0-17 + 0 03 pH units) that has previously been attributed to the upregulation of the Na+-H+ exchanger.3. Increasing perfusate osmolarity by addition of 60 mm sucrose caused a 19 + 2 % decrease in cell volume and a sustained increase in pHi (0 12 + 0 01 pH units) that was abolished by 1 mM amiloride. Acid loading experiments indicated that the increase in pHi was due to an alkaline shift in the pH dependence of the Na+-H+ exchanger. 4. A 20 % reduction in perfusate osmolarity prevented the cell shrinkage normally associated with ACh stimulation and largely abolished the ACh-induced increase in pHi. 5. Steady-state Na+-H+ exchanger activity, estimated from the initial rate of change in pHi following addition of amiloride, increased 9-fold during stimulation with ACh. When cell shrinkage was prevented by simultaneous exposure to the hypotonic solution, the activity of the exchanger still increased 7-fold in response to ACh. 6. We conclude that, although cell shrinkage leads to upregulation of the Na+-H+ exchanger, this factor alone is insufficient to account for the marked increase in exchanger activity that follows muscarinic stimulation.

Defective Fluid Secretion and NaCl Absorption in the Parotid Glands of Na+/H+ Exchanger-deficient Mice

“…Previous in vitro studies in mouse parotid acinar cells directly established that NHE1 is the Na ϩ /H ϩ exchanger isoform up-regulated by muscarinic receptor stimulation (29) and thus is the exchanger most likely to have a major role in modulating the rate of secretion (23,35,36). The present in vivo functional studies revealed that the knockout of Nhe1 gene expression inhibited pilocarpine-induced salivary flow, with the magnitude of the inhibition increasing during sustained stimulation.…”

Bicarbonate transport in sheep parotid secretory cells.

“…8). This contrasts with other mammalian salivary glands in which a shift in the pH activation curve of the exchanger enables it to maintain H+ extrusion at elevated values of pH, (Manganel & Turner, 1989;Steward et al 1989;Okada et al 1991;Seo et al 1995). From this we conclude that, in the sheep parotid, where pHi rises above the resting level during sustained stimulation, the Na+-H+ exchanger is unlikely to be any more active than in the resting condition and may indeed be less active.…”

Membrane‐limited expression and regulation of Na+‐H+ exchanger isoforms by P2 receptors in the rat submandibular gland duct

“…Therefore, when possible, it is important to verify findings made by immunostaining with additional independent techniques such as RT‐PCR analysis and measurement of activity, as reported here. Hence, based on our combined findings we conclude that SMG acinar cells express only NHE1 in the BLM, which probably mediates the acetylcholine‐ and cell shrinkage‐mediated, amiloride‐sensitive alkalization in these cells (Seo et al 1995).…”