Carbenoxolone and 18β-glycyrrhetinic acid inhibit inositol 1,4,5-trisphosphate-mediated endothelial cell calcium signalling and depolarise mitochondria

Background and Purpose: Coordinated endothelial control of cardiovascular function is proposed to occur by endothelial cell communication via gap junctions and connexins. To study intercellular communication, the pharmacological agents carbenoxolone (CBX) and 18 beta-glycyrrhetinic acid (18 beta GA) are used widely as connexin inhibitors and gap junction blockers. Experimental Approach: We investigated the effects of CBX and 18 beta GA on intercellular Ca2+ waves, evoked by inositol 1,4,5-trisphosphate (IP3) in the endothelium of intact mesenteric resistance arteries. Key Results: Acetycholine-evoked IP3-mediated Ca2+ release and propagated waves were inhibited by CBX (100 mu M) and 18 beta GA (40 mu M). Unexpectedly, the Ca2+ signals were inhibited uniformly in all cells, suggesting that CBX and 18 beta GA reduced Ca2+ release. Localised photolysis of caged IP3 (cIP(3)) was used to provide precise spatiotemporal control of site of cell activation. Local cIP(3) photolysis generated reproducible Ca2+ increases and Ca2+ waves that propagated across cells distant to the photolysis site. CBX and 18 beta GA each blocked Ca2+ waves in a time-dependent manner by inhibiting the initiating IP3-evoked Ca2+ release event rather than block of gap junctions. This effect was reversed on drug washout and was unaffected by small or intermediate K+-channel blockers. Furthermore, CBX and 18 beta GA each rapidly and reversibly collapsed the mitochondrial membrane potential. Conclusion and Implications: CBX and 18 beta GA inhibit IP3-mediated Ca2+ release and depolarise the mitochondrial membrane potential. These results suggest that CBX and 18 beta GA may block cell-cell communication by acting at sites that are unrelated to gap junctions.

Automated summary

The study showed that CBX and 18 beta GA inhibit intercellular communication by blocking IP3-mediated Ca2+ release and depolarising the mitochondrial membrane potential. This effect can be reversed upon drug washout and is not affected by K+-channel blockers.