Intracellular pH in lizards after hypercapnia

Abstract

We used the transmembrane distribution of 5,5-[2-14C]dimethyloxazolidine-2,4-dione ([14C]DMO) and 31P magnetic resonance spectroscopy (NMR) to investigate the effects of hypercapnia on intracellular pH (pHi) in brain and skeletal muscle of two lizard species: Anolis equestris and Dipsosaurus dorsalis. In control animals (normocapnic), plasma PCO2 (3.3 +/- 0.1 kPa) and plasma pH (7.52 +/- 0.01) for D. dorsalis were not significantly different from the values for A. equestris (2.8 +/- 0.2 kPa and 7.59 +/- 0.02, respectively). Furthermore 60 min of 5% CO2 increased plasma PCO2 and decreased plasma pH by the same amounts in both species. Brain pHi values determined with the DMO method were not significantly different from values determined with NMR. Control values of brain pHi (DMO, 7.16 +/- 0.01; NMR, 7.11 +/- 0.02) and muscle pHi were significantly higher for D. dorsalis (DMO, 7.15 +/- 0.03) than for A. equestris (DMO, 6.99 +/- 0.03; NMR, 7.02 +/- 0.02 for brain; DMO, 6.97 +/- 0.03 for muscle). In addition, changes in tissue pHi after 60 min of 5% CO2 were significantly different for the two species. In D. dorsalis muscle and brain pHi decreased significantly after hypercapnia, whereas in A. equestris muscle pHi decreased significantly but brain pHi was unchanged. Our findings were independent of the methods used to determine pHi. The smaller change in brain and muscle pHi than in plasma pH for A. equestris is consistent with the view that pHi regulation involves active processes such as transmembrane ion transport.(ABSTRACT TRUNCATED AT 250 WORDS)