Microfluorimetric imaging study of the mechanism of activation of the Na+/H+ antiport by muscarinic agonist in rat mandibular acinar cells.
The mechanism of regulation of intracellular pH (pHi) in dispersed acini from the rat mandibular salivary gland has been studied with a microfluorimetric imaging method and the pH probe 2',7'-bis(2-carboxyethyl)-5(and -6)-carboxyfluorescein. The pHi in the TRIS/HEPES-buffered standard solution was 7.29 +/- 0.01. Addition of 1 mumol/l acetylcholine (ACh) or ionomycin caused a sustained increase in the pHi. These agents decreased pHi in the absence of external Na+ or in the presence of amiloride. The rate of pHi recovery from an acid load after NH+4 prepulse was a linear function of pHi and increased as pHi became more acidic. Addition of ACh shifted the relationship towards a more alkaline pHi range. The increase in pHi induced by ACh or ionomycin was not inhibited by the protein kinase C inhibitors staurosporine (10 nM) and 1-(5-isoquinolinesulfonyl)-1-methylpiperazine (50 mumol/l). Addition of 0.1-1 mumol/l phorbol 12-myristate 13-acetate (TPA) had little effect on pHi within 10 min; however, exposure to TPA for 120 min resulted in a significant rise in pHi. In Ca(2+)-free solution with 50 mumol/l 8-(diethylamino)-octyl-3,4,5-trimethoxybenzoate, the ACh-induced rise in both pHi and cytosolic Ca2+ concentration was suppressed. ACh and ionomycin caused an increment of amiloride-sensitive acid output into the extracellular fluid, while 20 mumol/l 1-oleoyl-2-acetylglycerol had little effect on it. It was concluded that (a) stimulation with ACh activated the Na+/H+ antiport in the plasma membrane, (b) ACh also stimulated the intracellular acid production but acid extrusion by the Na+/H+ antiport prevented the cell from intracellular acidification, and (c) the major route of signal transduction for the ACh-induced activation of the Na+/H+ antiport was independent of protein kinase C but was dependent on the rise in cytosolic Ca2+ concentration. The implication of the cytosolic acidification and cell volume change in pHi regulation is discussed.
Okada
M
M
Department of Physiology, Tohoku University School of Medicine, Sendai, Japan.
Saito
Y
Y
Sawada
E
E
Nishiyama
A
A
D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D005110:Extracellular Space / Q000378:metabolism; D005470:Fluorometry; D006863:Hydrogen-Ion Concentration; D015759:Ionomycin / Q000494:pharmacology; D008297:Male; D010277:Parasympathomimetics / Q000494:pharmacology*; D011493:Protein Kinase C / Q000378:metabolism; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D012469:Salivary Glands / Q000166:cytology / Q000378:metabolism*; D017923:Sodium-Hydrogen Exchangers
D002352:Carrier Proteins; D010277:Parasympathomimetics; D000644:Quaternary Ammonium Compounds; D017923:Sodium-Hydrogen Exchangers; D015759:Ionomycin; D011493:Protein Kinase C; D000109:Acetylcholine; D002118:Calcium