Purified rat serosal mast cells contain 18.20 ± 3.90 (mean ± 1 S.D.) units of cyclic AMP-dependent protein kinase and 2.34 ± 0.46 (mean ± 1 S.D.) units of cyclic AMP-independent protein kinase/108 cells. The heat stable inhibitor protein from rabbit skeletal muscle completely inhibits the cyclic AMP-dependent protein kinase and partially inhibits cyclic AMP-independent protein kinase, thereby establishing that more than 94% of rat mast cell protein kinase is cyclic AMP dependent. After subcellular fractionation, 89.2 ± 2.2% (mean ± 1 S.D.) of the total mast cell protein kinase activity was in the cytosol fraction, and this enzyme was fully activatable by cyclic AMP. Anion-exchange chromatography of the rat mast cell cytosol protein kinase identified two isoenzymes with a modest preponderence of Type 1 cyclic AMP-dependent protein kinase over Type 2. Gel filtration was employed to separate the holoenzymes (R2C2) from the free catalytic subunit (C) and to calculate an activity ratio, the activity of the catalytic subunit divided by the total enzyme activity, which reflects the extent of activation of the holoenzymes. The mean activity ratio rose from 0.133 ± 0.056 (mean ± 1 S.D.) for mast cells exposed to normal rabbit IgG to 0.332 ± 0.053 (p < 0.001) for cells challenged with rabbit IgG anti-rat F(ab’)2, indicating the immunologic activation of cyclic AMP-dependent protein kinase. Further, histamine release from mast cells challenged with increasing concentrations of heat-inactivated rabbit anti-rat F(ab’)2 was inversely related to the remaining cellular concentrations of cyclic AMP-dependent protein kinase. Thus, the cytosol of purified rat serosal mast cells contains cyclic AMP-dependent protein kinase activity, which is activated by immunologic challenge.
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Holgate et al. (1980) studied this question.