A unique fluorescent phenylalkylamine probe for L-type Ca2+ channels. Coupling of phenylalkylamine receptors to Ca2+ and dihydropyridine binding sites.
The first fluorescently labeled phenylalkylamine, DMBODIPY-PAA (5-(3-[3-(4,4-difluoro-5,7-dimethyl-3a, 4a-diaza-4-bora-indacen-3-yl)propionamido] phenethyl-N-methylamino)-2-isopropyl-2-(3,4,5-trimethoxyphenyl)-valer onitrile) has been introduced for L-type Ca2+ channel research. DMBODIPY-PAA binds reversibly to L-type Ca2+ channels purified from rabbit skeletal muscle microsomes by wheat germ agglutinin-Sepharose chromatography. In this preparation DMBODIPY-PAA labels 412 pmol of phenylalkylamine receptors/mg of protein with a Kd of 6.82 nM and a favorable signal-to-noise ratio. Therefore DMBODIPY-PAA has a higher affinity for purified Ca2+ channels than the commonly employed radioligands and consequently has assisted in channel purification after prelabeling by simply monitoring receptor-bound fluorescence. (+)-PN200-110 (which is stimulatory for (-)-[3H]desmethoxyverapamil binding to purified Ca2+ channels) inhibits DMBODIPY-PAA labeling. Since these drug interactions are reciprocal, the phenylalkylamine and dihydropyridine binding sites of the alpha 1-subunit are tightly coupled. Kinetic and equilibrium binding studies with (-)-[3H]desmethoxyverapamil and DMBODIPY-PAA show that phenylalkylamine binding to L-type Ca2+ channels is dependent on Ca2+. Chelation of divalent metal ions converts phenylalkylamine receptors into a very low affinity state. This conversion is temperature- and time-dependent and completely reversible (K0.5 for free Ca2+ = 58 nM). This study demonstrates the utility of fluorescent ligands for binding studies with L-type Ca2+ channels and provides evidence for coupling between Ca2+ binding sites and phenylalkylamine receptors.
Knaus
H G
HG
Institute for Biochemical Pharmacology, Innsbruck, Austria.
Moshammer
T
T
Kang
H C
HC
Haugland
R P
RP
Glossmann
H
H
D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000378:metabolism*; D002846:Chromatography, Affinity; D004095:Dihydropyridines / Q000378:metabolism*; D005456:Fluorescent Dyes; D007700:Kinetics; D008861:Microsomes / Q000378:metabolism; D009132:Muscles / Q000378:metabolism; D009570:Nitriles / Q000138:chemical synthesis / Q000378:metabolism*; D010627:Phenethylamines / Q000138:chemical synthesis / Q000378:metabolism*; D011817:Rabbits; D011869:Radioligand Assay
D015220:Calcium Channels; D004095:Dihydropyridines; D005456:Fluorescent Dyes; D009570:Nitriles; D010627:Phenethylamines; C072556:5-(3-(3-(4,4-difluoro-5,7-dimethyl-3,4-diaza-4-bora-indacen-3-yl)propionamido)phenethyl-N-methylamino)-2-isopropyl-2-(3,4,5-trimethoxyphenyl)valeronitrile; C038806:1,4-dihydropyridine; D002118:Calcium