Intracellular calcium mobilization in rat platelets is adversely affected by copper deficiency

Abstract

The influence of copper deficiency on the mobilization of Ca 2+ from intracellular stores following ionomycin treatment or thrombin activation of rat platelets was examined using the fluorescent indicator, fura-2, to measure changes in cytosolic Ca 2+ concentration ([Ca 2+] i). Platelets, obtained from copper-deficient and control rats and loaded with fura-2, were suspended in medium containing 1 mM EGTA and no added Ca 2+. The size of the internal Ca 2+ pools in the suspended platelets was estimated from the rise in [Ca 2+] i following maximal discharge of stored Ca 2+ by treatment with 1 μM ionomycin. Peak [Ca 2+] i following ionomycin treatment was lower in platelets from copper-deficient rats compared to control rats ( 148 ± 27 nM vs. 188 ± 17 nM ), suggesting that the size of the Ca 2+ storage pools was decreased by copper deficiency. Furthermore, once internal Ca 2+ stores were discharged by ionomycin, [Ca 2+] i remained elevated in platelets from copper deficient rats, but decreased in control rats. These data indicate that copper deficiency may inhibit the efflux of Ca 2+ from platelets after its release from internal stores by ionomycin treatment. In platelets from copper-deficient and control rats, stimulation with 0.1 U / ml thrombin led to rapid rise followed by a slow decay in [Ca 2+] i. However, peak [Ca 2+] i was lower in platelets from copper-deficient rats than in control rats ( 94 ± 19 nM vs. 131 ± 16 nM ). These findings imply that by reducing the amount of Ca 2+ available for release from intracellular stores, copper deficiency also reduces [Ca 2+] i following thrombin activation in the absence of external Ca 2+.