Objective: To identify K⁺ channels of smooth muscle of human umbilical artery using the patch-clamp technique and to study their effect on resting tone of umbilical artery rings.

Methods: Whole-cell and single-channel patch-clamp recordings in enzymatically isolated smooth muscle cells were made. Measurements of developed isometric force were performed on intact tissue.

Results: Delayed rectifier K⁺ channels (K_DR) and large-conductance Ca²⁺-activated K⁺ channels (BK_Ca) contribute to the whole-cell voltage-and time-dependent outward K⁺ current, as it was specifically inhibited by 5 mM 4-aminopyridine (4-AP; K_DR blocker) (92 ± 4% at 0 mV, n = 7), by 1 mM tetraethylammonium (TEA; BK_Ca blocker) (71 ± 4% at +60 mV, n = 4), and by 200 nM iberiotoxin (BK_Ca blocker) (64 ± 7% at +60 mV, n = 4). In outside-out patches, BK_Ca channels had ā single-channel conductance of 132 ± 4 pS (n = 24) in asymmetric K⁺ conditions and 216 ± 4 pS (n = 4) in a symmetric K⁺ gradient. The activity of the BK_Ca channels was significantly augmented by 1 μM Ca²⁺ in the inside-out configuration. 4-AP had no effect on resting tone of intact arterial rings. TEA produced contraction of arterial rings whereas phloretin, an activator of BK_Ca, relaxed them, which means that BK_Ca channels are functional in intact tissue and are involved in the maintenance of resting tone in this human vessel.

Conclusion: The identities of K⁺ channels in the human umbilical artery were shown using the patch-clamp technique, and the physiologic effect of K⁺ channels on resting tone was documented.

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Potassium Channels in Human Umbilical Artery Cells