Extracellular and intracellular pH with changes of temperature in the dogfish Scyliorhinus stellaris

Larger Spotted Dogfish, Scyliorhinus stellaris, were exposed to varied ambient temperature (t) in order to determine the behavior of extracellular pH (pHe), Pco2 and bicarbonate concentration as well as intracellular pH (pHi) in three muscle types. pHe was found to vary with temperature slightly less than expected on the basis of the rule of constant relative alkalinity in juvenile (deltapH/deltat= -0.0148 per degree centigrade) as well as in adult (deltapH/deltat= -0.0136) fish. The absolute pHe values of adult fish were about 0.08 pH units higher than in juvenile fish. Arterial pco2 increased with rising temperature, the increase being much more marked in adult than in juvenile fish. Extracellular bicarbonate concentration (calculated from the pH and Pco2 values measured in arterial blood) was not maintained constant, but diminished in juvenile and increased in adult fish with increasing temperature, indicating that extracellular pH in dogfish is regulated by variations of both Pco2 and bicarbonate concentration. Variations of intracellular pH with temperature (deltapHi/deltat), -0.0178 for white muscle, -0.0334 for red muscle, and -0.0098 for heart muscle, were significantly different from the values of the extracellular compartment and, except for white muscle, significantly different from the condition for constant relative alkalinity (deltapH/deltat= -0.0183). These results are in agreement with the rule of constant relative alkalinity with respect to extracellular pH and possibly also with respect to an overall mean intracellular pH, but the rule is not quantitatively followed by the individual body compartments and tissues.