Effects of elevated pressures of inert gases on cytosolic free Ca2+ of human platelets stimulated with ADP

Platelets were exposed to elevated pressures of helium (He), nitrogen (N2), and He/xenon (He/Xe, 85/15), and stimulated with ADP (5 microM). He to 36 atmospheres absolute (ATA) inhibited the ADP-stimulated increase in [Ca2+]i, measured by Fura-2/AM, with most of the effect occurring by 9 ATA. N2 caused a similar but initially greater effect and it was bimodal, with inhibition being less at 36 ATA than at 18 ATA. N2 also significantly depressed basal levels at 18 and 36 ATA. In the He/Xe mixture, the effect on ADP-stimulated [Ca2+]i was no different from He alone at the same pressures, but basal levels were significantly depressed. In a calcium-free medium both He and N2 moderately depressed the already-reduced response to ADP stimulation but only N2 significantly depressed basal levels at all pressures. These results indicate that raised pressures of inert narcotic gases, as well as pressure per se (represented by He), can affect cell [Ca2+]i sufficiently to have physiological consequences. This, together with previous findings in this laboratory, may have implications for some of the neurological problems associated with deep diving.