Role of protein kinase C in bradykinin-induced increases in microvascular permeability

The goal of this study was to determine whether protein kinase C mediates bradykinin-induced increases in microvascular permeability. Permeability of the hamster cheek pouch was evaluated using intravital fluorescent microscopy and fluorescein isothiocyanate (FITC)-dextran (MW 70,000). We examined effects of sphingosine, a protein kinase C inhibitor, on bradykinin-induced increases in permeability. Increases in permeability were quantitated by counting the number of leaky sites and calculating the clearance of FITC-dextran. During bradykinin (10^-6 M), leaky sites increased from 0 to 40 ± 4 (mean ± SEM) sites/0.11 cm², and clearance increased from 1.7 ± 1.0 to 22 ± 9 ml/sec X 10^-6. The bradykinin type-2 receptor antagonist D-Arg,[Hyp³,Thi^5,8,D-Phe⁷]-bradykinin virtually abolished formation of leaky sites in response to bradykinin. To determine whether changes in microvascular pressure contribute to the increase in leaky sites, venular pressure was measured using a micropipette and survo-null device. Increases in cheek pouch venular pressure were similar during application of bradykinin and adenosine, which increased permeability, and isoproterenol, which did not increase permeability in the cheek pouch. Thus, increases in permeability were not linked to changes in microvascular pressure. The protein kinase C inhibitor, sphingosine (10^-6 M), markedly attenuated responses to bradykinin. Leaky sites increased from 0 to only 2 ± 1 sites/0.11 cm², and clearance increased from 3.9 ± 1.4 to only 6.7 ± 2.2 ml/sec X 10^-6. To test the specificity of sphingosine, we examined effects of adenosine (10^-6 M). Sphingosine did not significantly alter increases in microvascular permeability in responses to adenosine. We also examined effects of 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H-7), another protein kinase C inhibitor, on responses to bradykinin and adenosine. H-7 greatly attenuated formation of leaky sites during stimulation with bradykinin and did not alter the number of leaky sites produced during adenosine. The findings suggest that protein kinase C may mediate increases in vascular permeability in response to bradykinin.