The mold Neurospora crassa ATCC 5297a was grown in gaseous environments of helium, neon, argon, krypton, xenon, or nitrogen containing approximately 5 percent oxygen. A close correlation of the growth rate R (in millimeters per hour at 30 degrees C) with the molecular weight MW of the chemically inert gas was observed. This correlation is described by the empirical equation: R = 3.88 - 0.1785 (MW).

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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

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BUCHHEIT, R. G. (Union Carbide Corp., Tonawanda, N.Y.), H. R. SCHREINER, AND G. F. DOEBBLER. Growth responses of Neurospora crassa to increased partial pressures of the noble gases and nitrogen. J. Bacteriol. 91:622-627. 1966.-Growth rate of the fungus Neurospora crassa depends in part on the nature of metabolically "inert gas" present in its environment. At high partial pressures, the noble gas elements (helium, neon, argon, krypton, and xenon) inhibit growth in the order: Xe > Kr > Ar >> Ne >> He. Nitrogen (N2) closely resembles He in inhibitory effectiveness. Partial pressures required for 50% inhibition of growth were: Xe (0.8 atm), Kr (1.6 atm), Ar (3.8 atm), Ne (35 atm), and He (-300 atm). With respect to inhibition of growth, the noble gases and N2 differ qualitatively and quantitatively from the order of effectiveness found with other biological effects, i.e., narcosis, inhibition of insect development, depression of 02-dependent radiation sensitivity, and effects on tissue-slice glycolysis and respiration. Partial pressures giving 50% inhibition of N. crassa growth parallel various physical properties (i.e., solubilities, solubility ratios, etc.) of the noble gases. Linear correlation of 50% inhibition pressures to the polarizability and of the logarithm of pressure to the first and second ionization potentials suggests the involvement of weak intermolecular interactions or charge-transfer in the biological activity of the noble gases.