Effects of tetrandrine on calcium channel currents of bovine chromaffin cells.
Calcium channel currents of bovine chromaffin cells are blocked by the bis-benzyl-isoquinoline alkaloid tetrandrine, which is isolated from the roots of the chinese medical herb Stephania tetrandra. The half-maximal inhibition (IC50) occurred at a concentration of about 10 microM. Bovine chromaffin cells possess no low-voltage-activated, but different types of high-voltage activated calcium channel currents. Tetrandrine blocks omega-conotoxin-sensitive N-type, dihydropyridine-sensitive L-type and omega-conotoxin- and dihydropyridine-insensitive calcium channel currents of chromaffin cells. The I/V relationship in not shifted by tetrandrine, indicating that the block is not voltage-dependent. After tetrandrine application the currents become transient in a depolarization- and a concentration-dependent manner. Tetrandrine blocks open calcium channels and the block is use-dependent. When the holding potential returns to resting levels, the channels are unblocked in about 1 sec.
Medical Institute of Environmental Hygiene, Heinrich-Heine-University, Düsseldorf, Germany.
F
F
Weinsberg
U
U
Bickmeyer
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H
Wiegand
D000470:Alkaloids / Q000494:pharmacology*; D000818:Animals; D044182:Benzylisoquinolines; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D002417:Cattle; D002478:Cells, Cultured; D004759:Enterochromaffin Cells / Q000187:drug effects / Q000378:metabolism*; D018408:Patch-Clamp Techniques
D000470:Alkaloids; D044182:Benzylisoquinolines; D002121:Calcium Channel Blockers; D015220:Calcium Channels; C009438:tetrandrine