Preferential intracellular pH regulation: Hypotheses and perspectives
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Issue Date
2016-08
Editor
Authors
Shartau, Ryan B.
Baker, Daniel W.
Crossley, Dane A. II
Brauner, Colin J.
License
Subject
Abstract
The regulation of vertebrate acid–base balance during acute
episodes of elevated internal PCO2 is typically characterized by
extracellular pH (pHe) regulation. Changes in pHe are associated with
qualitatively similar changes in intracellular tissue pH (pHi) as the two
are typically coupled, referred to as ‘coupled pH regulation’. However,
not all vertebrates rely on coupled pH regulation; instead, some
preferentially regulate pHi against severe and maintained reductions
in pHe. Preferential pHi regulation has been identified in several adult
fish species and an aquatic amphibian, but never in adult amniotes.
Recently, common snapping turtles were observed to preferentially
regulate pHi during development; the pattern of acid–base regulation
in these species shifts from preferential pHi regulation in embryos to
coupled pH regulation in adults. In this Commentary, we discuss the
hypothesis that preferential pHi regulation may be a general strategy
employed by vertebrate embryos in order to maintain acid–base
homeostasis during severe acute acid–base disturbances. In adult
vertebrates, the retention or loss of preferential pHi regulation may
depend on selection pressures associated with the environment
inhabited and/or the severity of acid–base regulatory challenges to
which they are exposed. We also consider the idea that the retention
of preferential pHi regulation into adulthood may have been a key
event in vertebrate evolution, with implications for the invasion of
freshwater habitats, the evolution of air breathing and the transition of
vertebrates from water to land.