Hypertonic saline solutions attenuate agonist-induced changes of intracellular calcium

The proper fluid for resuscitation of hemorrhagic shock is still controversial. Hypertonic saline solutions would cause an impairment of platelet function, aggravating blood loss in case of uncontrolled hemorrhage. This work examines the in vitro effect of hypertonic NaCl solutions on the changes in [Ca2+]i induced by 100 microM ADP, 0.1 IU/ml thrombin or 0.5 microM ionomycin in human platelets. Furthermore, it was investigated if the addition of NaCl reduces the mobilization from intracellular stores or the calcium entry from extracellular media. In a solution containing 1 mM CaCl2, the increase of [Ca2+]i produced by thrombin was 93, 75 or 55% of the 300 mosM control when osmolarity of the solution was 350, 400, or 500 mosM, respectively. The calcium signal induced by ADP decreased more rapidly in hypertonic media than in isotonic solution. In a calcium-free solution, the mobilization of stored calcium produced by thrombin was reduced when osmolarity was increased from 300 mosM to 350, 400 or 500 mosM by 86, 75 or 45% of the control, respectively. The increase of [Ca2+]i produced by subsequent introduction of 1 mM extracellular calcium was also reduced. Similar effects were found when platelets were stimulated by ADP. Instead, the capacitative calcium entry induced by ionomycin was increased in 500 mosM media by a 138% of the isotonic control. The decrease in the Ca2+ signal produced by receptor agonists in hypertonic media may play a role in the reduction of platelet responses such as aggregation or shape change when hypertonic resuscitation fluids are utilized.