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

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