Calcium channels: the beta-subunit increases the affinity of dihydropyridine and Ca2+ binding sites of the alpha 1-subunit.
A Ca2+ channel alpha 1-subunit derived from rabbit heart was transiently expressed in COS-7 cells. The dihydropyridine (+)-isradipine had low affinity (Ki = 34.3 nM) for the alpha 1-subunit in the absence of the beta-subunit due to rapid dissociation (k-1 = 0.11 min-1). Co-expression of the beta-subunit resulted in a > 35-fold increase in (+)-isradipine binding affinity (Ki = 0.9 nM) due to decreased dissociation (k-1 of 0.007 min-1). Higher DHP binding affinity was associated with an increase of the apparent affinity of Ca2+ ions for the channel. Our data suggest that the beta-subunit affects the coordination of Ca2+ ions with sites that are coupled to the dihydropyridine binding domain and by this mechanism increases the affinity for these ligands.
Mitterdorfer
J
J
Institut für Biochemische Pharmakologie, Universität Innsbruck, Austria.
Froschmayr
M
M
Grabner
M
M
Striessnig
J
J
Glossmann
H
H
D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D018076:DNA, Complementary; D004095:Dihydropyridines / Q000378:metabolism*; D015870:Gene Expression; D007700:Kinetics; D009206:Myocardium / Q000378:metabolism; D014162:Transfection
D015220:Calcium Channels; D018076:DNA, Complementary; D004095:Dihydropyridines; C038806:1,4-dihydropyridine; D002118:Calcium