K⁺ current inhibition by prostacyclin analog carbacyclin in baroreceptor neurons requires g-protein activation and CAMP formation

Prostacyclin (PGI₂) increases baroreceptor (BR) sensitivity in vivo. We have previously shown that the stable PGI₂ analog carbacyclin (CC) inhibits Ca²⁺-activated K⁺ current in isolated BR neurons and the effect is blocked by a specific inhibitor of cAMP-dependent protein kinase (PKA). In this study we tested the hypothesis that the mechanism involves binding of CC to G-protein coupled receptors on BR neurons and subsequent formation of CAMP. Aortic BR neurons in nodose ganglia were labeled and identified by their uptake of fluorescent dye (Di-I) applied to adventitia of rat aortic arch 1 -2 weeks prior to dissociation of nodose neurons. Whole cell patch-clamp techniques were used to record outward K⁺ current elicited by 200 rrts voltage step from -60 to +40 mV. CC (0.1 mM) inhibited outward K current to 64±4% of control (n=8, p<0.01)- Replacing GTP in (he intracellular (pipette) solution with GDP-β-S (0.5 mM) to prevent Gprotein activation abolished CC-induced inhibition of the K⁺ current (n=4). The inhibitory effect of CC was mimicked by direct activation of G-proteins with intracellular application of GTP-γ-S (n=3). Exposure of BR neurons to the membrane permeable cAMP analog 8-bromo-cAMP (1-5 mM) inhibited the K⁺ current significantly (n=6). These results indicate thai CC-induccd inhibition of K⁺ current in BR neurons is mediated by activation of a G-protein and cAMP/PKA pathway.