The helium group gases and nitrous oxide at superatmospheric pres- In a systematic study of the effects of the helium group gases on linear growth of Neurospma crassa, Schreiner, Gregoire and Lawrie ('62) showed that helium group gases depressed the rate of growth as a function of the square root of the molecular weight. These observations were extended by Buchheit, Schreiner and Doebbler ('66) by employing these gases at higher pressures. They obtained a linear correlation between the 50% inhibitory pressure and polarizability of the gases.Observations of such physico-chemical regularities have provided much of the data for theories of general anesthesia, with polarizability being considered at least indirectly in most of them (Featherstone and Muehlbaecher, '63). On the other hand, biochemical investigations have not yet contributed significantly to understanding the mechanism of action. If mammalian cells in culture respond to inert gases in a manner described by physico-chemical parameters that correlate with anesthetic potency, as do growth rates of N . crassa, a useful model would be available for a biochemical approach. For that reason, we have examined the effects of the helium group gases on attachment and multiplication of HeLa cells in monolayer culture.In addition to helium group gases, we have also studied nitrous oxide in an effort to explore possible differences in the biological mode of action between monoatomic and polyatomic anesthetic gases.J. CELL. PXYSIOL., 69: 385-392. MATERIALS AND METHODSHeLa cells (Gey) were cultured in Eagle's spinner medium (Eagle, '59) containing 10% fetal calf serum as inoculum for growth experiments. Growth response was measured on monolayer cultures. Five roller tubes and one Leighton tube with coverslip were inoculated with 1 X los cells in 1 ml of Eagle's minimum essential medium containing 10% fetal calf serum. The six tubes were assembled into a 1-liter stainless steel pressure vessel. Six of these vessels were used in each experiment. The vessels were charged with the appropriate test gas by evacuating and filling with premixed gases. All gas mixtures were analyzed to contain 0.2 atm 02, 0.05 atm CO,, and 0.75 atm test gas. In the pressure experiments, pure gas was added to the vessels after they had been charged with the gas mixture at 1 atm.The cell population increase after three days at 37°C was determined by counting cells attached to the glass tubes. After removing the medium, the attached cells Received Feb. 9. '67. Accepted April 11. '67. 1These studies were su ported in part by Contract Nonr 4115(00) between tl?e Office of Naval Research. Department of the Navy, and Union Carbide Corporation.2