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Purified calcium channels have three allosterically coupled drug receptors
Author(s) -
Striessnig J.,
Goll A.,
Moosburger K.,
Glossmann H.
Publication year - 1986
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(86)80327-1
Subject(s) - allosteric regulation , dihydropyridine , chemistry , receptor , diltiazem , stereochemistry , calcium channel , binding site , voltage dependent calcium channel , calcium , biophysics , biochemistry , biology , organic chemistry
(−)‐[ 3 H]Desmethoxyverapamil and (+)‐[ 3 P]PN 200‐110 were employed to characterize phenylalkylamineselective and 1,4‐dihydropyridine‐selective receptors on purified Ca 2+ channels from guinea‐pig skeletal muscle t ‐tubules. In contrast to the membrane‐bound Ca 2+ channel, d‐ cis ‐diltiazem (EC 50 = 4.5 ± 1.7 μM) markedly stimulated the binding of (+)‐[ 3 H]PN 200‐110 to the purified ionic pore. In the presence of 100 μM d‐ cis ‐diltiazem (which binds to the benzothiazepine‐selective receptors) the B max for (+)‐[ 3 H]PN 200‐110 increased from 497 ± 81 to 1557 ± 43 pmol per mg protein, whereas the K d decreased from 8.8 ± 1.7 to 4.7 ± 1.8 nM at 25°C. P‐ cis ‐Diltiazem was inactive. (−)‐Desmethoxyverapamil, which is a negative heterotropic allosteric inhibitor of (+)‐[ 3 H]IN 200‐110 binding to membrane‐bound channels, stimulated 1,4‐dihydropyridine binding to the isolated channel. (−)‐[ 3 H]Desmethoxyverapamil binding was stimulated by antagonistic 1,4‐dihydropyridines [(+)‐PN 200‐110 ⪢(−)(CR)‐202‐791 ⪢(+)(4 R )‐Bay K 8644] whereas the agonistic enantiomers (+)( S )‐202‐791 and (−)(4 S )‐Bay K 8644 were inhibitory and (−)‐PN 200‐110 was inactive. The results indicate that three distinct drug‐receptor sites exist on the purified Ca 2+ channel, two of which are shown by direct labelling to be reciprocally allosterically coupled.