Metabolic correlates of intracellular pH change during rapid contractile activity in a molluscan muscle

Intracellular pH (pH i ) changes during burst contractile activity in in vitro preparations of phasic adductor muscle of the bay scallop, Argopecten irradians concentricus , were monitored using phosphorus nuclear magnetic resonance ( 31 P‐NMR) spectroscopy. A transient alkalinization (from pH i 7.06 to 7.15) was observed during the first period of contractions. The predominant mode of adenosine triphosphate (ATP) production during this period was by hydrolysis of arginine phosphate, a proton consuming process. Subsequent contractions of the muscle resulted in a gradual acidification, with pH i approaching 6.94. During these later stages of contraction, glycolytic production of octopine was a major source of ATP. The net proton yields of energy transformations were estimated, based on proton consumption by arginine phosphate utilization and proton yield of octopine production. The resulting predicted pattern of proton change was very similar to those of observed changes in pH i . Intracellular pH changes during contractile activity in A. irradians concentricus phasic adductor muscle are strongly correlated with the pattern of proton yield of metabolic energy transformations taking place in the tissue.