Inhibition of the calcium pump by high cytosolic Ca super(2+) in intact human red blood cells

• Published in: The Journal of physiology 1993-01, Vol.461, p.63-73
• Main Authors: Pereira, A C, Samellas, D, Tiffert, T, Lew, V L
• Format: Article
• Language: English
• ISSN: 0022-3751

The inhibitory effect of high intracellular calcium on the saturated Ca super(2+) efflux through the Ca super(2+) pump (V sub(max)) was investigated in intact human red cells. Cells were loaded with Ca super(2+) by exposure to the calcium ionophore A23187, at different external Ca super(2+) concentrations ([Ca super(2+)] sub(o)). Ca super(2+) extrusion by the pump was followed after either ionophore removal or Co super(2+) addition. Fifty per cent inhibition of V sub(max) was obtained with total intracellular calcium ([Ca sub(T)] sub(i)) of ) 3 mmol/l cells. For any given initial Ca super(2+) load, V sub(max) showed no tendency to increase as [Ca sub(T)] sub(i) was progressively reduced during Ca super(2+) efflux. This suggests that the pump V sub(max) was determined by the magnitude of the initial [Ca super(2+)] sub(i). To estimate [Ca super(2+)] sub(i) from [Ca sub(T)] sub(i) in Co super(2+)-loaded cells, the possible competition between Co super(2+) and Ca super(2+) for the known cytoplasmic Ca super(2+) buffers ( alpha -buffers) was investigated first. Comparison between Ca super(2+) efflux after either Co super(2+) exposure or ionophore wash-out showed that the efflux patterns were essentially identical, down to the lowest measurable [Ca sub(T)] sub(i). This indicates that Co super(2+) does not compete with Ca super(2+) for the alpha -buffers.