1H- and 31P-NMR studies on smooth muscle of bullfrog stomach

31P-NMR spectra of bullfrog stomach smooth muscle showed peaks for creatine phosphate (4.8 mumol X g-1 wet wt.), ATP (3.6), inorganic phosphate (Pi, 2.4), phosphomonoesters (3.0) and phosphodiesters (3.3). The intracellular pH was 7.3, and calculated from the chemical shift of Pi. 1H-NMR spectra of smooth muscle yielded peaks of 2.9 for lactate, 6.6 for total creatine (creatine phosphate + creatine) and methyl protons of choline tentatively assigned to glycerolphosphorylcholine or to membrane phospholipids. Creatine phosphate and ATP decreased under anaerobic conditions, and intracellular acidification was observed with the concomitant increase in lactate. 31P saturation transfer studies showed that saturation of the gamma-ATP resonance reduced the intensity of creatine phosphate to 60% of its control value, and the measured T1 value of creatine phosphate was 2.4 s with saturation. The calculated forward flux of the creatine kinase reaction (decomposition direction of creatine phosphate) was 0.77 mumol X g-1 wet wt. X s-1. The creatine kinase flux was approx. 100-times larger than the ATP turnover rate, calculated from the oxygen consumption rate with the assumption, P/O = 3. In conclusion, the creatine kinase reaction is at equilibrium in resting smooth muscle of bullfrog stomach.