The effect of papaverine on ion channels in rat basilar smooth muscle cells

Objectives: Papaverine has been used in treating vasospasm following subarachnoid hemorrhage (SAH). However, its action mechanism for cerebral vascular relaxation is not clear. Potassium and calcium channels are closely related to the contraction and relaxation of cerebral smooth muscle. Therefore, to identify the role of potassium and calcium channels in papaverine-induced vascular relaxation, we examined the effect of papaverine on potassium and calcium channels in freshly isolated smooth muscle cells from rat basilar artery. Method: The isolation of rat basilar smooth muscle cells was performed by special techniques. The whole cell currents were recorded by whole cell patch clamp technique in freshly isolated smooth muscle cells from rat basilar artery. Papaverine was added to the bath solution. Results: Papaverine of 100 μM into bath solution increased the amplitude of the outward K⁺ current which was completely blocked by BKCa blocker, IBX (iberiotoxin) and a calcium chelator, BAPTA (1,2-bis(o-aminophenoxy) ethane-N,N,N′,N′- tetraacetic acid) in whole cell mode. Papaverine (100 μM) also inhibited L type Ca²⁺ current recorded in isolated smooth muscle cells from rat basilar artery. Discussion: These results strongly suggest that Ca ²⁺-activated potassium channels and L type Ca²⁺ channels may be involved in papaverine-induced vascular relaxation in rat basilar artery.