Effects of elevated pressures of inert gases on cytosolic free Ca2+ of cultured human neuroblastoma cells stimulated with carbachol: relevance to high pressure neurological syndrome.

Suspended cells of the human neuroblastoma line SK-N-SH were exposed to elevated pressures of non-narcotic helium (He) and the narcotic gases nitrogen (N2), and argon (Ar) and stimulated with carbachol. He, 18 and 36 atmospheres absolute (ATA), equivalent to 544 and 1120 feet of seawater, potentiated the increase in [Ca2+]i induced by carbachol, as measured by Fura-2. Carbachol-stimulated increases in [Ca2+]i were not significantly altered from values in 1 ATA air by either N2 or Ar at the same pressures. The response to carbachol of cells exposed to 36 ATA of He and slowly decompressed to 1 ATA was indistinguishable from that of cells never exposed to pressure. Thus this pressure-potentiated increase in [Ca2+]i is compatible with excitation, is reversible and is not elicited by narcotic gases. It was observed, moreover, at pressures encountered by commercial deep-sea divers. The High Pressure Neurological Syndrome (HPNS) encountered by divers breathing He/O2 mixtures at high pressures, and its known antagonism by N2, may be due in part to effects on neuronal [Ca2+]i levels since an increase in these would most likely result in an excitatory response.