Using Ehrlich ascites tumour cells, the short-term effects of the therapeutic glucocorticoid Methylprednisolone (MP) on the cellular energy metabolism were studied. ATP-consuming processes involved in the rapid MP effects were identified indirectly from the effects of MP on cellular oxygen consumption related to the inhibition of respiration by selective inhibitors of Ca2+-ATPase and protein synthesis. The effects of MP on plasma membrane permeability for Ca2+ ions and phospholipid turnover were studied directly by using confocal laser scanning microscopy and tracerkinetic measurements, respectively. MP inhibited cellular oxygen consumption, suppressed the inhibitory effect of lanthanum but not that of cycloheximide on oxygen consumption, blocked the [Ca2+]i rise in response to calcium ionophore A 23187, and decreased phospholipid turnover. MP acted instantly in a dose-dependent manner.

The observed effects of MP are discussed in relation to the hypothesis that the drug has direct membrane effect affecting plasma membrane permeability and function.

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