Interaction of tetrandrine with slowly inactivating calcium channels. Characterization of calcium channel modulation by an alkaloid of Chinese medicinal herb origin

Tetrandrine, a bis-benzylisoquinoline alkaloid derived from the Chinese medicinal herb Stephania tetrandra, is a putative Ca2+ entry blocker whose mechanism of action is unknown. To investigate this mechanism, the effects of tetrandrine were characterized on binding of three chemical classes of Ca2+...

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Bibliographic Details
Published in:The Journal of biological chemistry 1988-02, Vol.263 (5), p.2238-2244
Main Authors: King, V F, Garcia, M L, Himmel, D, Reuben, J P, Lam, Y K, Pan, J X, Han, G Q, Kaczorowski, G J
Format: Article
Language:English
Subjects:
Alkaloids - pharmacology
Animals
Benzylisoquinolines
Biological and medical sciences
calcium
Calcium - metabolism
calcium antagonists
Cell physiology
Diltiazem - metabolism
Drugs, Chinese Herbal - pharmacology
Fundamental and applied biological sciences. Psychology
Gallopamil - metabolism
heart
herbal medicines
Ion Channels - drug effects
Ion Channels - metabolism
Kinetics
Membrane and intracellular transports
membrane vesicles
Molecular and cellular biology
Myocardium - metabolism
Nitrendipine - metabolism
Plants, Medicinal
sarcolemma
Sarcolemma - metabolism
Swine
tetrandrine
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Summary:Tetrandrine, a bis-benzylisoquinoline alkaloid derived from the Chinese medicinal herb Stephania tetrandra, is a putative Ca2+ entry blocker whose mechanism of action is unknown. To investigate this mechanism, the effects of tetrandrine were characterized on binding of three chemical classes of Ca2+ entry blockers in cardiac sarcolemmal membrane vesicles. In the range 25-37 degrees C, tetrandrine completely blocks diltiazem binding, partially inhibits D-600 binding, and markedly stimulates nitrendipine binding, with greatest enhancement occurring at 37 degrees C. The potency of tetrandrine is increased 10-fold as temperature is raised from 25 to 37 degrees C. Scatchard analyses indicate that inhibition of diltiazem binding and stimulation of nitrendipine binding result from changes in ligand affinities while inhibition of D-600 binding is due to both an increase in KD and decrease in Bmax of aralkylamine receptors. Ligand dissociation studies reveal that tetrandrine increases D-600 off-rates, decreases nitrendipine off-rates, but has no effect on diltiazem dissociation kinetics. In addition, tetrandrine reversibly blocks inward Ca2+ currents through L-type Ca2+ channels in GH3 anterior pituitary cells. These results indicate that tetrandrine interacts directly at the benzothiazepine-binding site of the Ca2+ entry blocker receptor complex and allosterically modulates ligand binding at other receptors in this complex. These findings suggest that tetrandrine is a structurally unique natural product Ca2+ entry blocker and provide a rationale explanation for the therapeutic effectiveness of this agent.
ISSN:0021-9258
1083-351X
DOI:10.1016/S0021-9258(18)69196-3