J. exp. Bwl. 148, 303-312 (1990) 303 Printed in Great Britain © The Company of Biologists Limited 1990 THE TEMPERATURE DEPENDENCE OF THE ADRENERGIC Na + /H + EXCHANGER OF TROUT ERYTHROCYTES BY A. R. COSSINS AND R. V. KILBEY Environmental Physiology Research Group, Department of Environmental and Evolutionary Biology, University of Liverpool, PO Box 147, Liverpool L69 3BX Accepted 21 September 1989 Summary The effects of temperature upon the adrenergic Na + /H + exchange of rainbow trout erythrocytes have been studied in vitro. The initial rates of H + ejection and of increase of intracellular Na + ([Na + ],) in adrenergically stimulated cells were highly temperature-dependent, with apparent Arrhenius activation energies of 112.8±10.0 (mean±s.D., N=4) and 84.113.0kJmoP 1 (N=3), respectively. The steady-state [Na + ]j following stimulation decreased progressively with cooling, whilst the time required for [Na + ], to return to control values after removal of agonist was greatly increased. The change in intracellular pH resulting from adrenergic stimulation was reduced by cooling, such that at 4°C adrenergic responses were barely measurable. The effect of temperature upon the steady- state [Na + ], and pHi was probably caused by a disparity in the temperature dependence of the transport mechanisms that contribute to the respective steady states. Introduction Adrenergic agonists induce a rapid increase in intracellular Na + concentration of trout erythrocytes from approximately lOmmolP 1 packed cell volume (pcv) to a new steady state of 50-80 mmoll" 1 . This is coupled to the ejection of H + from the cell and so constitutes a Na + /H + exchange mechanism with a stoichiometry of 1 (Baroin etal. 1984; Cossins and Richardson, 1985; Motais and Garcia-Romeu, 1988). The resulting efflux of H + disturbs the HCO 3 ~ distribution away from its electrochemical equilibrium and induces a net flux of HCO 3 ~, via the fast anion exchange mechanism, in exchange for Cl~. Thus, there is a net loss of H + and HCO 3 ~ from the cell and a gain of NaCl, which is associated with a swelling. Because the net H + loss exceeds the loss of HCO 3 ~ there is a distinct intracellular alkalinization which alters the oxygen-binding properties of haemoglobin (Cossins and Richardson, 1985; Salama and Nikinmaa, 1988). Virtually all in vitro studies to date have been performed at 15-20°C, which for rainbow trout represent high but sub-lethal temperatures. The effects of acute Key words: Na + /H + exchanger, trout erythrocyte, temperature, adrenergic responses.