Intracellular pH in lizard Dipsosaurus dorsalis in relation to changing body temperatures

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Abstract
Mean whole-body and tissue-specific intracellular pH values (pHi) were measured in Dipsosaurus dorsalis by the dimethyloxazolidinedione technique. pHi was measured in lizards at constant body temperatures (Tb) (18, 25, 35, and 42 degrees C) and in lizards undergoing changes in Tb between 18 and 42 degrees C. Constant Tb between 18 and 42 degrees C maintained for 24 h or more produced a delta pH/delta Tb of -0.015 for the mean whole-body, -0.012 for venous blood, -0.0104 for cardiac muscle, and -0.0098 for skeletal muscle. Within the preferred range of Tb values (35–42 degrees C), the delta pH/delta Tb patterns were closer to that expected to achieve constant dissociation of protein imidazole (approximately -0.017): mean whole-body -0.020, cardiac muscle -0.016, and skeletal muscle -0.018. Tissue water contents were independent of Tb. Whole-body pHi during gradual warming and cooling (approximately 2 h elapsed time for each direction) closely corresponded to steady-state values. Upon cooling to 18 degrees C, tissue-specific and whole-body pHi often fell 0.1–0.2 unit below that expected; in each case this was correlated with an extracellular acidosis. A gradual recovery of pHi occurred with the recovery of the extracellular acidosis. Over the normally experienced Tb range, adjustments in pHi apparently rapidly achieve steady-state values and are in accord with the imidazole alphastat hypothesis. These patterns are discussed in terms of the thermal ecology of Dipsosaurus.