Kinetics of the sodium pump in red cells of different temperature sensitivity.

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Abstract
Ouabain-sensitive K influx into ground squirrel and guinea pig red cells was measured at 5.degree. and 37.degree. C as a function of external K and internal Na. In both species the external K affinity increases on cooling, being 3- and 5-fold higher in guinea pig and ground squirrel, respectively, at 5.degree. than at 37.degree. C. Internal Na affinity also increased on cooling, by about the same extent. The effect of internal Na ([Na]i) on ouabain-sensitive K influx in guinea pig cells fits a cubic Michaelis-Menten-type equation, but in ground squirrel cells this was true only at high [Na]i. There was still significant ouabain-sensitive K influx at low [Na]i. Ouabain-binding experiments indicated .apprx. 800 sites/cell for guinea pig and Columbian ground squirrel erythrocytes, and 280 sites/cell for 13-lined ground squirrel cells. There was no significant difference in ouabain bound per cell at 37.degree. and 5.degree. C. Calculated turnover numbers for Columbian and 13-lined ground squirrel and guinea pig red cell Na pumps at 37.degree. C were about equal, being 77-100 and 100-129 s-1, respectively. At 5.degree. C red cells from ground squirrels performed significantly better, the turnover numbers being 1.0-2.3 s-1 compared with 0.42-0.47 s-1 for erythrocytes of guinea pig. The results do not accord with a hypothesis that cold-sensitive Na pumps are blocked in 1 predominant form.