Carbon monoxide and cultured rat heart cells II. Interaction of carbon monoxide and hypoxia on growth and contractile activity

Cultured rat heart muscle cells treated for 16 days with concentrations of over 19% carbon monoxide in the gas phase maintained their beating rate in direct proportion to the concentration of carbon monoxide. Reduction of oxygen to either 2.5 or 5% significantly reduced their beating rate after 6 days of treatment. The lowest concentration of oxygen employed (2.5%) combined with the highest concentration of carbon monoxide (75%) produced no significant action on the beating rate over that of the hypoxia alone. The effects of carbon monoxide on cell growth, as measured by changes in total protein and DNA of either muscle or endothelioid cell cultures, and cell toxicity, as measured by nonviable cell count, were also concentration dependent. Exposure of either heart muscle or heart endothelioid cell cultures to 2.5% or 5% oxygen also significantly reduced the amount of total protein or DNA. In contrast to the lack of a demonstrable interaction of carbon monoxide and hypoxia on muscle cell beating, a significant additive or potentiative effect on cell growth was obtained with concentrations of 75% carbon monoxide and either 2.5% or 5% oxygen.