American alligator (Alligator mississippiensis) embryos tightly regulate intracellular pH during a severe acidosis

Abstract

Crocodilian nests naturally experience high CO2(hypercarbia), which leads to increased blood Pco2and reduced blood pH (pHe) in embryos; their response to acid–base challenges is not known. During acute hypercarbia, snapping turtle embryos preferentially regulate tissue pH (pHi) against pHereductions. This is proposed to be associated with CO2tolerance in reptilian embryos and is not found in adults. In the present study, we investigated pH regulation in American alligator (Alligator mississippiensis (Daudin, 1802)) embryos exposed to 1 h of hypercarbia hypoxia (13 kPa Pco2, 9 kPa Po2). Hypercarbia hypoxia reduced pHeby 0.42 pH unit, while heart and brain pHiincreased, with no change in the pHiof other tissues. The results indicate that American alligator embryos preferentially regulate pHi, similar to snapping turtle embryos, which represents a markedly different strategy of acid–base regulation than what is observed in adult reptiles. These findings suggest that preferential pHiregulation may be a strategy of acid–base regulation used by embryonic reptiles.