The effects of hypercapnia on intracellular and extracellular acid-base status in the toad Bufo marinus

Toads (Bufo marinus) were exposed to environmental hypercapnia of 5% CO2 in air, and extracellular and intracellular acid-base parameters were determined 1 and 24 h after the onset of hypercapnia. The initial drop in pH was compensated by the elevation of extracellular and intracellular bicarbonate. Relating the pH compensation to the pH drop that is expected to occur by increased PCO2 at constant bicarbonate concentration, the pH compensation in the extracellular space was 30% and reached the following values for intracellular body compartments: 65% in skeletal muscle, 77% in heart muscle and 44% in skin. The additional bicarbonate was partly produced by blood and intracellular non-bicarbonate buffers; the major portion of the remainder was related to the excretion of ammonia into the environmental water. The hypercapnia-induced changes of pH were considerably smaller in all tissue cells than in the extracellular space. Thus Bufo marinus exhibits the relative preference of intracellular over extracellular acid-base regulation that has been observed in other vertebrates.