title: Modulation of Na(+)-H+ exchange by altered cell volume in perfused rat mandibular salivary gland.
abstract: 1. Intracellular pH (pHi) 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 microM acetylcholine (ACh) led to a 15 +/- 2% decrease in cell volume. A transient decrease in pHi 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.
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000143:Acids / Q000494:pharmacology; D000818:Animals; D002021:Buffers; D006863:Hydrogen-Ion Concentration; D006982:Hypertonic Solutions / Q000494:pharmacology; D007424:Intracellular Fluid / Q000378:metabolism; D008297:Male; D010477:Perfusion; D051381:Rats; D012469:Salivary Glands / Q000166:cytology* / Q000378:metabolism*; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism*
chemical_list: D000143:Acids; D002021:Buffers; D006982:Hypertonic Solutions; D017923:Sodium-Hydrogen Exchangers; D000109:Acetylcholine