科研之友
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摘要
Body temperature increases in ectothermic vertebrates characteristically lead to both increases in arterial P-CO2 (Pa-CO2) and declines in resting arterial pH (pHa) of about 0.017 pH units per 1 degrees C increase in temperature. This 'alphastat' pH pattern has previously been interpreted as being evolutionarily driven by the maintenance of a constant protonation state on the imidazole moiety of histidine protein residues, hence stabilizing protein structure-function. Analysis of the existing data for interclass responses of ectothermic vertebrates shows different degrees of Pa-CO2 increases and pH declines with temperature between the classes, with reptiles>amphibians>fish. The Pa-CO2 at the temperature where maximal aerobic metabolism (<(V)over dot>(O2),(max)) is achieved is significantly and positively correlated with temperature for all vertebrate classes. For ectotherms, the Pa-CO2 where <(V)over dot>(O2),(max) is greatest is also correlated with <(V)over dot>(O2),(max), indicating there is an increased driving force for CO2 efflux that is lowest in fish, intermediate in amphibians and highest in reptiles. The pattern of increased Pa-CO2 and the resultant reduction of pHa in response to increased body temperature would serve to increase CO2 efflux, O-2 delivery and blood buffering capacity and maintain ventilatory scope. This represents a new hypothesis for the selective advantage of arterial pH regulation from a systems physiology perspective in addition to the advantages of maintenance of protein structure-function.
- 出版日期2018-1
