Background:

Histamine stimulates microvascular macromolecule extravasation by binding to its GPCR receptors on endothelial cells. Atrial natriuretic peptide (ANP) through its cGMP- producing guanylyl cyclase-A (GC-A) receptor moderates this effect.

Objective:

To study the mediatory role of cGMP-dependent kinase I (cGKI) and its downstream endothelial targets.

Main results:

In wild type mice, ANP did not enhance the extravasation of fluorescent dextran from venules of the mouse cremaster muscle, but intensely reduced histamine - stimulated vascular leakage. This protective action of ANP against histamine-inflammation was abolished in mice with conditional, endothelial disruption of GC-A or cGKI. In cultured human dermal microvascular endothelial cells, histamine provoked a biphasic Ca²⁺ rise. Both the peak and plateau phase were lessened by either ANP or the cGKI activator, 8- Br-cGMP. Our in vivo studies with TRPC6 knockout mice demonstrated that TRPC6 channels are indispensable in systemic histamine-induced hyperpermeability. Moreover, the TRPC6 activator hyperforin mimicked the strong inflammatory actions of histamine. ANP markedly attenuated the responses to hyperforin. Consistently, ANP activated the cGKI-mediated inhibitory phosphorylation of TRPC6 channels at Thr69.

Conclusions:

Endothelial cGKI activation and inhibitory TRPC6 phosphorylation are critically involved in the barrier stabilizing effects of ANP in the systemic microcirculation.

Supported by SFB 688.