Activation of Epac/Rap1 attenuates venular permeability response to platelet activating factor (PAF) in vivo

Abstract

Stimulation of intracellular cAMP strongly inhibits acute permeability response induced by many inflammatory mediators including PAF. We have reported that both PKA-dependent and PKA-independent pathways are involved. A novel PKA-independent pathway is the activation of Epac, a cAMP specific guanine nucleotide exchange factor for the small GTPase Rap1. In cultured endothelial monolayers Rap1 increases cortical actin and promotes redistribution of tight junction and adherens junction components to cell-cell junctions (Blood, 2005; 105:–1955). The cAMP analog 8-pCPT-2′-O-Methyl-cAMP (O-Me-cAMP) is specific for the Epac/Rap1 pathway. We tested the efficacy in vivo of O-Me-cAMP to block PAF stimulated hyperpermeability in single rat mesentery post-capillary venules. We found that O-Me-cAMP significantly attenuates the PAF response as measured by hydraulic permeability (Lp) (p<0.05, n = 6, Wilcoxon). PAF alone increased Lp 25 ± 7-fold over baseline (0.47 ± 0.05 × 10-7 cm/(s×cmH2O); with O-Me-cAMP (100 μM, 30 min pretreatment) the PAF peak Lp was 8 ± 2-fold over baseline (mean ± SEM). Similar results were found with 500 μM O-Me-cAMP. We conclude that activation of the Epac/Rap1 pathway is a significant component of the activity of cAMP to block increased permeability in normal microvessels. This approach will enable further differentiation of PKA dependent and PKA independent mechanisms to regulate microvessel permeability. NIH HL28607