Ca2Â +-dependent potassium channels and cannabinoid signaling in the endothelium of apolipoprotein E knockout mice before plaque formation

Endothelial Ca2 +-dependent K+ channels (KCa) regulate endothelial function. We also know that stimulation of type 2 cannabinoid (CB2) receptors ameliorates atherosclerosis. However, whether atherosclerosis is accompanied by altered endothelial KCa- and CB2 receptor-dependent signaling is unknown. By utilizing an in situ patch-clamp approach, we directly evaluated the KCa channel function and the CB2 receptor-dependent electrical responses in the endothelium of aortic strips from young ApoE−/− and C57Bl/6 mice. In the ApoE−/− group, the resting membrane potential (− 30.1 ± 1.1 mV) was less negative (p < 0.05) compared to WT (− 38.9 ± 1.4 mV) and voltage ramps generated an overall KCa current of reduced amplitude. The peak hyperpolarization to 2 μM Ach was not different between the groups. However, the sustained component was significantly reduced in ApoE−/− strips. In contrast, the peak hyperpolarization to 0.2 μM Ach was increased in the ApoE−/− group, and SKA-31, a direct IKCa/SKCa channel opener, produced a hyperpolarization and whole-cell current of greater amplitude. The BKCa opener NS1619 produced hyperpolarization that was enhanced in ApoE−/− group. N-arachidonoyl glycine, a BKCa opener, produced a hyperpolarization of enhanced amplitude in ApoE−/− arteries. Selective CB2 receptor agonist AM1241 (5 μM) had no effect on endothelial membrane potential in WT group; however, in ApoE−/− group, it elicited hyperpolarization that was inhibited by a selective CB2 receptor antagonist AM630. Conclusively, our data point to functional down-regulation of basal IKCa activity in unstimulated endothelium of ApoE−/− mice. Direct and indirect IKCa stimulation resulted in increased recruitment of the channels. In addition, our data point to up-regulation of endothelial BKCa channels and CB2 receptors in ApoE−/− arteries.