Acetylcholine-induced metabolic changes in the perfused rabbit mandibular salivary gland studied by 31P-NMR spectroscopy.
Changes in the content of high-energy phosphates, intracellular pH (pHi) and the ratio of MgATP to total ATP ([MgATP]/[ATP]t) resulting from continuous stimulation with acetylcholine (10(-9) to 10(-4) M) were measured by 31P-NMR spectroscopy in the isolated, perfused rabbit mandibular gland at 37 degrees C. With 10(-9) to 10(-7) M acetylcholine, no significant changes in these parameters were observed. On stimulation with 10(-6) M acetylcholine, the optimal concentration for sustained secretion, the content of ATP decreased by 28 +/- 10% (mean +/- S.E.; n = 8) of its control value. pHi decreased initially by approx. 0.05 pH unit, then showed an alkalinization of 0.09 +/- 0.02 pH unit (n = 8). With 10(-5) and 10(-4) M acetylcholine, changes in ATP and pHi were similar to those induced by 10(-6) M acetylcholine: the total content of high-energy phosphates remained at approx. 70% of the control value and no decrease in [MgATP]/[ATP]t was observed. As possible causes of the reduced secretory rate observed with higher concentrations of acetylcholine (10(-5) to 10(-3) M), we can exclude depletion of high-energy phosphates, inhibition of metabolism caused by intracellular acidosis, and inhibition of ATP usage caused by a decrease in MgATP availability.
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Department of Physiological Sciences, University of Manchester, U.K.
Steward
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MC
Mackenzie
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Case
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D000109:Acetylcholine / Q000494:pharmacology*; D000244:Adenosine Diphosphate / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D005260:Female; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D010725:Phosphocreatine / Q000378:metabolism; D010758:Phosphorus; D011817:Rabbits; D013363:Submandibular Gland / Q000187:drug effects / Q000378:metabolism*
D010725:Phosphocreatine; D010758:Phosphorus; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D000109:Acetylcholine