The Effect of Tyrosine Kinase Inhibitors on the L-type Calcium Current in Rat Basilar Smooth Muscle Cells

OBJECTIVE: Tyrosine kinase inhibitors may be useful in the management of cerebral vasospasm. It has not yet been reported whether L-type Ca2+ channels play a role in tyrosine kinase inhibitors-induced vascular relaxation of cerebral artery. This study was undertaken to clarify the role of L-type Ca2+ channels in tyrosine kinase inhibitors-induced vascular relaxation, and to investigate the effect of tyrosine kinase inhibitors on L-type Ca2+ channels currents in freshly isolated smooth muscle cells from rat basilar artery. METHODS: 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. RESULTS: Patch clamp studies revealed a whole-cell current which resembles the L-type Ca2+ current reported by others. The amplitude of this current was decreased by nimodipine and increased by Bay K 8644. Genistein(n=5), tyrphostin A-23(n=3), A-25(n=6) 30micrometer reduced the amplitude of the L-type Ca2+ channel current in whole cell mode. In contrast, diadzein 30 micrometer (n=3), inactive analogue of genistein, did not decrease the amplitude of the L-type Ca2+ channels current. CONCLUSION: These results suggest that tyrosine kinase inhibitors such as genistein, tyrphostin A-23, A-25 may relax cerebral vessel through decreasing level of intracellular calcium, [Ca2+]i, by inhibition of L-type Ca2+ channel.

The Effect of Papaverine on the Calcium-dependent K+ Current in Rat Basilar Smooth Muscle Cells

OBJECTIVE: Papaverine has been used in treating vasospasm following subarachnoid hemorrhage(SAH). However, its action mechanism for cerebral vascular relaxation is not clear. Potassium 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 examine the effect of papaverine on potassium channels in freshly isolated smooth muscle cells from rat basilar artery. METHODS: 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 microM into bath solution increased the amplitude of the outward K+ current which was completely blocked by BKCa(large conductance calcium dependent potassium channels)blocker, IBX(iberiotoxin), and calcium chealator, BAPTA(1, 2-bis(o-aminophenoxy)ethane-N, N, N', N'-tetraacetic acid), in whole cell mode. CONCLUSION: These results strongly suggest that potassium channels may play roles in papaverine-induced vascular relaxation in rat basilar artery.

Effects of Tyrosine Kinase Inhibitors on the Calcium-Dependent K+ Current in Rat Basilar Smooth Muscle Cells

OBJECTIVE: Tyrosine kinase inhibitors may be useful in the management of cerebral vasospasm. It has not yet reported whether potassium channel plays a role in tyrosine kinase inhibitors-induced vascular relaxation of cerebral artery. This study is undertaken to clarify the role of potassium channel in tyrosine kinase inhibitors-induced vascular relaxation, and to investigate the effect of tyrosine kinase inhibitors on outward potassium currents in freshly isolated smooth muscle cells from rat basilar artery. METHODS: The isolation of rat basilar smooth muscle cells was performed by special techniques. The whole cell currents were recoreded by whole cell patch clamp technique in freshly isolated smooth muscle cells from rat basilar artery. RESULTS: In present study, genistein(n=10), tyrphostin A-23(n=10), A-25(n=10) 30microM into bath solution increased the amplitude of the outward K+ current which was completely blocked by large conductance calcium-activated potassium channel(BK(Ca)) blocker, iberiotoxin(0.1microM), and calcium chelator, BAPTA, in whole cell mode. In contrast, diadzein 30microM(n=10), inactive analogue of genistein, did not increase the amplitude of the outward K+ current. CONCLUSION: Our results suggest tyrosine kinase inhibitors such as genistein, tyrphostin A-23 and A-25 increase the BK(Ca) channel activity in cerebral basilar smooth muscle cells, thereby contributing to the relaxation of cerebral artery.