DISSIPATION OF THE CALCIUM GRADIENT IN HUMAN ERYTHROCYTES RESULTS IN INCREASED HEAT-PRODUCTION

Heat production rates were measured by a microcalorimetric method in s uspended human erythrocytes in the absence and presence of different c oncentrations of the divalent cationophore A23187. Determinations were carried out during 60 min under static conditions on erythrocytes inc ubated in various isotonic media at 37-degrees-C, pH 7.35. In incubati ons containing the ionophore, time-power curves showed an early peak f ollowed by a descending slope levelling off at a steady state after 30 -60 min. In contrast, the controls lacked the early peak, showing hype rbolic ascending curve profiles before reaching steady state. The appe arance of the early peak in the presence of ionophore was dependent up on the composition of the medium, both Mg2+ ions and glucose being dec isive. Likewise, dose-response relationships concerning heat productio n at 60 min depended on the composition of the media. In a basic incub ation medium lacking Mg2+ and glucose, no effect was seen on heat prod uction by the ionophore (1-3 mumol/l). Rather modest effects were obta ined by the ionophore at 2 and 3 mumol/l when Mg2+ was present. A clea r-cut dose-response relationship was observed in a Mg2+ and glucose en riched medium for the ionophore from 1-3 mumol/l. The significant incr ease in heat production observed at 60 min with 2 mumol/l of A23187 in the Mg2+ and glucose enriched medium was abolished by 1 mmol/l EGTA. Calmidazolium, a calmodulin antagonist, could only marginally reduce t he ionophoric effect on heat production. It was concluded that the app earance of the early peak was not the result of an increase in glycoly tic rate but rather a consequence of the ionophoric action on the Ca2 gradient.