In vitro relaxation of vascular smooth muscle by atropine: involvement of K+ channels and endothelium

Cumulative addition of atropine to the organ bath containing endothelium-intact (+E) rat aorta, which was precontracted with phenylephrine (PE, 1 μM) and subsequently relaxed with carbachol (1μM), caused biphasic changes in the vascular contractility of +E rat aortic rings. Low concentrations of atropine (10 nM–1.0 μM) caused progressive restoration of contraction to PE; whereas at higher concentrations (1–100 μM), atropine caused progressive …