ACTIVATION OF CAMP-DEPENDENT PROTEIN-KINASE IN EPIDERMIS BY THE COMPOUNDS WHICH INCREASE EPIDERMAL CAMP

[摘要] Pig epidermal slices were incubated with various compounds which increased epidermal cAMP, and the change in cAMP-dependent protein kinase activity ratio was studied by the method of Cherrington (1976) with modification. Epinephrine (5 .times. 10-5 M), histamine (10-4 M) and adenosine (10-3M), potent agonists of epidermal adenyl cyclase, fully activated the protein kinase (PK) during an incubation of 30-45 s, that was much shorter than that required for maximal cAMP accumulation under the same conditions (5 min). With such a brief stimulus, the epidermal cAMP-PK system did not become refractory and responded to repeated stimuli. Prostaglandin E2 (PGE2) and isobutylmethylxanthine (IBMX) and ethanol only partially activated the enzyme. Prostaglandin F2.alpha. (PGF2.alpha.) and theophylline which were much less effective in increasing epidermal cAMP, activated the enzyme to the same extent as PGE2 and and IBMX, respectively. Apparently, PK activation takes place in response to a cAMP increase in small locus of the cell. Such an increase in cAMP can be very small or even not measurable when measured as total cAMP in the tissue homogenate. Increases above this level may not be physiologic. Measurement of cAMP-dependent PK activity ratio may be a more direct and more sensitivie way to study the effect of compounds which act through cAMP mediated mechanisms.