PLATELET-ACTIVATING-FACTOR MODULATES MICROVASCULAR TRANSPORT BY STIMULATION OF PROTEIN-KINASE-C

To investigate the possible involvement of protein kinase C (PKC) in p latelet-activating factor (PAF)-stimulated microvascular responses, PK C inhibitors, sphingosine (SPH), 1-(5-isoquino-linylsulfonyl)-3-methyl piperazine (iso H-7), and calphostin C, were applied topically to the hamster cheek pouch, and PAF-elicited changes in microvascular permsel ectivity and arteriolar constriction were evaluated. Pretreatment with 10(-6) M SPH, 10(-5) M SPH, or 10(-10) M iso H-7 significantly reduce d 10(-7) M PAF-induced increase in fluorescein isothiocyanate-Dextran 150 clearance (2,677.3 +/- 397.3, 2,985.3 +/- 350.7, and 2,689.3 +/- 2 56.0 vs. 4,784.0 +/- 474.7 nl.60 min(-1).g(-1), respectively). Calphos tin C at 10(-7) M attenuated 10(-8) M PAF-induced increase in clearanc e (2,156.9 +/- 353.3 vs. 3,841.6 +/- 260.9 nl.60 min(-1).g(-1)). Perme ability changes were also measured by integrated optical intensity (IO I). Pretreatment with 10(-6) M SPH, 10(-5) M SPH, or 10(-10) M iso H-7 attenuated the maximal increment in IOI induced by 10(-7) M PAF (2,02 4.0 +/- 364.4, 1,690.0 +/- 525.2, and 2,432.8 +/- 655.3 vs. 4,255.9 +/ - 695.6 U, respectively). Direct stimulation of PKC by phorbol dibutyr ate increased clearance in dose-dependent fashion. Similarly, activati on of PKC with phorbol myristate acetate increased IOI values. The PAF -induced arteriolar constriction was not blocked by the PKC inhibitors . Our results suggest that PKC represents a biochemical pathway involv ed in the PAF modulation of microvascular permeability but not of arte riolar constriction.