INVOLVEMENT OF PROTEIN-KINASE-C IN THE CONTROL OF MICROVASCULAR PERMEABILITY TO COLLOIDAL CARBON

The vasculature of the rat small intestine and attached mesentery was perfused in vitro with a gelatin-containing physiological salt solutio n (GPSS). The inclusion of colloidal carbon (CC) in the perfusate towa rds the end of the experimental period enabled the ''leakiness'' of mi crovessels in the villi to be determined, since ''leaky'' vessels trap CC in their walls. Addition to the perfusate of the inflammatory agon ists platelet-activating factor (PAF, 5 x 10(-6) M) or 5-hydroxytrypta mine (5-HT, 1 x 10(-4) M), or the microtubule-disrupting agents podoph yllotoxin (5 x 10(-5) M), or colcemid (5 x 10(-5) M), or the protein k inase C (PKC) activator phorbol 12, 13-dibutyrate (PDB, 1 x 10(-6) M), caused significantly increased microvascular ''blackening'' as assess ed by image analysis. 4alpha-phorbol 12, 13-didecanoate (PDD, 1 x 10(- 6) M) had no effect. Pretreatment with the PKC inhibitor Ro 31-8820 (1 x 10(-6) M) significantly reduced the effects of PAF, 5-HT and PDB, b ut not those of podophyllotoxin or colcemid. These results suggest, th erefore, that PKC is involved in the permeability-enhancing effects of PAF, 5-HT and PDB. Pretreatment with indomethacin (1 x 10(-6) M)as a cyclooxygenase inhibitor did not reduce the response to PDB, indicatin g that prostaglandin release is of minor importance in the PDB-induced increase in microvascular permeability.