Intracellular and extracellular acid-base status as a function of temperature in the freshwater channel catfish, Ictalurus punctatus.

The relationship between acid-base status and temperature was studied in the channel catfish, Ictalurus punctatus. The change in blood pH with temperature had a slope of -0.0132/degrees C and involved both a decrease in total CO2 at higher temperatures, and a significant rise in arterial PCO2. The acid-base changes in the intracellular compartment were similar to those in the blood, except that for red and white muscle the slope of the change in pH with temperature had a slightly higher value (-0.0185 and -0.0147, respectively), and for heart muscle it had a smaller value (-0.0117). The net whole-body excretion of acid or base in response to temperature change was relatively small: 0.40 m-mole . kg-1 net OH- was excreted in response to an increase from 22 to 31 degrees C, and 0.31 m-mole . kg-1 net H+ was excreted in response to change from 25 to 15 degrees C. In both cases approximately half was excreted renally and half branchially. Using information on the volumes and buffer capacities of the various body fluid compartments as well as the information above, the ratio of imidazole to phosphate intracellular buffers was calculated to be 5.1 to 1. The amount of intercompartmental (active) transfer required to make temperature adjustments is strongly dependent on the buffer ratio, and on the PCO2. Without the observed changes in PCO2 with temperature, the transfer requirement would have been 3 to 4 times larger.