Temperature-dependent changes of chloride transport kinetics in human red cells.

Abstract

Chloride self-exchange in human red cells was studied between 0.degree. C and 38.degree. C. At higher temperatures the flow-tube method was used. Although the general features of chloride transport at 0.degree. C and 38.degree. C are similar, the following differences were found: the maximum pH of chloride self-exchange flux was lowered 0.6 pH unit from 7.8 to 7.2 when temperature was increased from 0.degree. C to 38.degree. C; the apparent half-saturation constant increased from 28 mM at 0.degree. C to 65 mM at 38.degree. C; chloride transport at body temperature is slower than predicted by other investigators by extrapolation from low-temperature results. Chloride transport increased only 200 times when temperature was raised from 0.degree. C to 38.degree. C, because the apparent activation energy decreased from 30 kcal mol-1 to 20 kcal mol-1 above a temperature of 15.degree. C; a study of temperature dependence of the slower bromide self-exchange showed that a similar change of activation energy occurred around 25.degree. C. Both in the case of Cl- (15.degree. C) and in the case of Br- (25.degree. C), critical temperature was reached when the anion self-exchange had a turnover number of about 4 .cntdot. 109 ions cell-1 s-1; inhibition of chloride transport by DIDS (4,4''-diisothiocyano-stilbene-2,2''-disulfonate) revealed that the deflection persisted at 15.degree. C at partial inhibition (66%) presumably because DIDS inactivated 66% of the transport sites. A less temperature-dependent step of anion exchange may become rate limiting at the temperature where a critical turnover number is reached.