Abstract
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 18β-glycyrrhetinic acid (18βGA) are used widely as connexin inhibitors and gap junction blockers. EXPERIMENTAL APPROACH: We investigated the effects of CBX and 18βGA on intercellular Ca(2+) waves, evoked by inositol 1,4,5-trisphosphate (IP(3) ) in the endothelium of intact mesenteric resistance arteries. KEY RESULTS: Acetycholine-evoked IP(3) -mediated Ca(2+) release and propagated waves were inhibited by CBX (100 μM) and 18βGA (40 μM). Unexpectedly, the Ca(2+) signals were inhibited uniformly in all cells, suggesting that CBX and 18βGA reduced Ca(2+) release. Localised photolysis of caged IP(3) (cIP(3) ) was used to provide precise spatiotemporal control of site of cell activation. Local cIP(3) photolysis generated reproducible Ca(2+) increases and Ca(2+) waves that propagated across cells distant to the photolysis site. CBX and 18βGA each blocked Ca(2+) waves in a time-dependent manner by inhibiting the initiating IP(3) -evoked Ca(2+) 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 18βGA each rapidly and reversibly collapsed the mitochondrial membrane potential. CONCLUSION AND IMPLICATIONS: CBX and 18βGA inhibit IP(3) -mediated Ca(2+) release and depolarise the mitochondrial membrane potential. These results suggest that CBX and 18βGA may block cell-cell communication by acting at sites that are unrelated to gap junctions.