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 IP3-evoked intercellular
Ca2+ waves in the endothelium of intact mesenteric
resistance arteries. Key Results Acetylcholine (ACh)-evoked
IP3-mediated Ca2+ release and
propagated waves were inhibited by CBX (100µM) and 18βGA (40µM).
Unexpectedly, the Ca2+ signals were inhibited
uniformly in all cells, suggesting that CBX and 18βGA reduced
Ca2+ release. Localised photolysis of caged
IP3 (cIP3) was used to provide precise
spatiotemporal control of site of cell activation. Local
cIP3 photolysis generated reproducible
Ca2+ increases and Ca2+ waves that
propagated across cells distant to the photolysis site. CBX and 18βGA
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
18βGA each rapidly and reversibly collapsed the mitochondrial membrane
potential. Conclusion and Implications CBX and 18βGA inhibit
IP3-mediated Ca2+ release and
depolarise the mitochondrial membrane potential. These results suggest
that CBX and 18βGA block cell-cell communication by acting at sites that
are unrelated to gap junctions.