Dissipation of the calcium gradient in human erythrocytes results in increased heat production

Abstract

Heat production rates were measured by a microcalorimetric method in suspended human erythrocytes in the absence and presence of different concentrations of the divalent cationophore A23187. Determinations were carried out during 60 min under static conditions on erythrocytes incubated in various isotonic media at 37°C, pH 7.35. In incubations containing the ionophore, time-power curves showed an early peak followed by a descending slope levelling off at a steady state after 30–60 min. In contrast, the controls lacked the early peak, showing hyperbolic ascending curve profiles before reaching steady state. The appearance of the early peakk in the presence of ionophore was dependent upon the composition of the medium, both Mg 2+ ions and glucose being decisive. Likewise, dose-response relationships concerning heat production at 60 min depended on the composition of the media. In a basic incubation medium lacking Mg 2+ and glucose, no effect was seen on heat production by the ionophore (1–3 μmol/l). Rather modest effects were obtained by the ionophore at 2 and 3 μmol/l when Mg 2+ was present. A clear-cut dose-response relationship was observed in a Mg 2+ and glucose enriched medium for the ionophore from 1–3 μmol/l. The significant increase in heat production observed at 60 min with 2 μmol/l of A23187 in the Mg 2+ and glucose enriched medium was abolished by 1 mmol/l EGTA. Calmidazolium, a calmodulin antagonist, could only marginally reduce the ionophoric effect on heat production. It was concluded that the appearance of the early peak was not the result of an increase in glycolytic rate but rather a consequence of the ionophoric action on the Ca 2+ gradient.