EXHAUSTIVE EXERCISE IN THE SEA LAMPREY (PETROMYZON-MARINUS) - RELATIONSHIP BETWEEN ANAEROBIC METABOLISM AND INTRACELLULAR ACID-BASE-BALANCE

We measured intracellular acid-base balance and indicators of carbohyd rate and high-energy phosphate metabolism as lampreys recovered from e xhaustive exercise. A combined respiratory and metabolic acidosis was observed in the locomotory muscle following 'burst' exercise. Muscle p H decreased from approximately 7.2 to 6.7, whereas intracellular P(CO2 ) rose from approximately 0.6 to 1.6 kPa. Unlike the situation in simi larly stressed teleost fish such as rainbow trout, the respiratory aci dosis in muscle persisted for several hours. This apparent CO2 retenti on in lamprey muscle may be the result of a restricted ability of the circulatory system to transport CO2 due to reduced erythrocyte anion e xchange, or it could represent a restricted ability of the muscle itse lf to clear the intracellular pool Of CO2 due to reduced carbonic anhy drase activity. Maximal lactate dehydrogenase activity of lamprey musc le exhibited a marked dependence on pH, increasing in activity by 30 % as pH decreased from 7.2 to 6.7 (reflecting the 'resting' to 'post-ex ercise' pH change observed in vivo). Following exhaustive exercise, th e acid-base balance of the muscle is influenced by both proton-consumi ng (e.g. AMP deamination, glycogen replenishment) and proton-producing (e.g. rephosphorylation of creatine) metabolic processes. The net eff ect is that, although intracellular pH is maximally depressed, energy stores such as phosphocreatine and glycogen are partially restored wit hin 1 h of exhaustive exercise, placing the animal in good stead for f urther locomotory work.