beta-Adrenergic stimulation of salmonid red cells results in a rapid decrease (within 5 min) in the nucleotide triphosphate:haemoglobin ratio (NTP:Hb), which is thereafter maintained at a constant level, presumably through increased ATP turnover via matched aerobic metabolism and energy-consuming processes. Addition of the beta-adrenergic agonist isoproterenol to rainbow trout red cells in vitro leads to a rise in intracellular pH (pHi), a corresponding decrease in extracellular pH (pHe) and an increase in red cell oxygen consumption (MO2). Moreover, the extent to which red cell pHi is maintained constant in the face of an acute extracellular acidosis in vitro or in vivo is proportional to the adrenergically stimulated increase in red cell MO2. In the absence of oxygen, these red cells remain capable of pH regulation, but cannot maintain NTP:Hb constant. As a result, membrane and metabolic functions become uncoupled in the stimulated deoxygenated cells.

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