Temperature sensitivity of cyclic AMP production and catecholamine-induced refractoriness in a rat astrocytoma cell line

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Intracellular cyclic AMP was increased more than 100-fold when rat C6-2B astrocytoma cells were treated with isoproterenol in the cold (4°C). When the cells were treated with the phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine, and isoproterenol, cyclic AMP levels rose more than 150-fold. The levels achieved compared favorably with the 250-fold increase in cyclin AMP produced by (-)isoproterenol at 37°C.(-)Isoproterenol at 5 nM stimulated half-maximal cyclic AMP production at 4°C and at 37°C and was blocked by (-)propranolol at both temperatures. The concentrations of cyclic AMP attained by these cells after (-)isoproterenol stimulation in the cold may be accounted for, in part, by alterations in the efflux of the nucleotide from the cells since extracellular cyclic AMP, an indicator of cyclic AMP efflux, was found to be dramatically reduced in the cold.

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