Background and Purpose The calcium-activated potassium channel K Ca3.1 is expressed in the vascular endothelium where its activation causes endothelial hyperpolarization and initiates endothelium-derived hyperpolarization (EDH)-dependent dilatation. Here, we investigated whether pharmacological activation of K Ca3.1 dilates skeletal muscle arterioles and whether myoendothelial gap junctions formed by connexin40 (Cx40) are required for EDH-type dilatations and pressure depressor responses in vivo. Experimental Approach We performed intravital microscopy in the cremaster muscle microcirculation and blood pressure telemetry in Cx40-deficient mice. Key Results In wild-type mice, the K Ca3.1-activator SKA-31 induced pronounced concentration-dependent arteriolar EDH-type dilatations, amounting to ∼40% of maximal dilatation, and enhanced the effects of ACh. These responses were absent in mice devoid of K Ca3.1 channels. In contrast, SKA-31-induced dilatations were not attenuated in mice with endothelial cells deficient in Cx40 (Cx40 fl/fl:Tie2-Cre). In isolated endothelial cell clusters, SKA-31 induced hyperpolarizations of similar magnitudes (by ∼38 mV) in Cx40 fl/fl:Tie2-Cre, ubiquitous Cx40-deficient mice (Cx40 -/-) and controls (Cx40 fl/fl), which were reversed by the specific K Ca3.1-blocker TRAM-34. In normotensive wild-type and Cx40 fl/fl:Tie2-Cre as well as in hypertensive Cx40 -/- animals, i.p. injections of SKA-31 (30 and 100 mg·kg -1) decreased arterial pressure by ∼32 mmHg in all genotypes. The depressor response to 100 mg·kg -1 SKA-31 was associated with a decrease in heart rate. Conclusions and Implications We conclude that endothelial hyperpolarization evoked by pharmacological activation of K Ca3.1 channels induces EDH-type arteriolar dilatations that are independent of endothelial Cx40 and Cx40-containing myoendothelial gap junctions. As SKA-31 reduced blood pressure in hypertensive Cx40-deficient mice, K Ca3.1 activators may be useful drugs for severe treatment-resistant hypertension.