Calcium channel block by (-)devapamil is affected by the sequence environment and composition of the phenylalkylamine receptor site.
The pore-forming alpha 1 subunit of L-type calcium (Ca2+) channels is the molecular target of Ca2+ channel blockers such as phenylalkylamines (PAAs). Association and dissociation rates of (-)devapamil were compared for a highly PAA-sensitive L-type Ca2+ channel chimera (Lh) and various class A Ca2+ channel mutants. These mutants carry the high-affinity determinants of the PAA receptor site in a class A sequence environment. Apparent drug association and dissociation rate constants were significantly affected by the sequence environment (class A or L-type) of the PAA receptor site. Single point mutations affecting the high-affinity determinants in segments IVS6 of the PAA receptor site, introduced into a class A environment, reduced the apparent drug association rates. Mutation I1811M in transmembrane segment IVS6 (mutant AL25/-I) had the highest impact and decreased the apparent association rate for (-)devapamil by approximately 30-fold, suggesting that this pore-lining isoleucine in transmembrane segment IVS6 plays a key role in the formation of the PAA receptor site. In contrast, apparent drug dissociation rates of Ca2+ channels in the resting state were almost unaffected by point mutations of the PAA receptor site.
Degtiar
V E
VE
Institut für Biochemische Pharmakologie, Innsbruck, Austria.
Aczél
S
S
Döring
F
F
Timin
E N
EN
Berjukow
S
S
Kimball
D
D
Mitterdorfer
J
J
Hering
S
S
D000818:Animals; D001665:Binding Sites; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D015220:Calcium Channels / Q000737:chemistry / Q000187:drug effects / Q000502:physiology*; D020746:Calcium Channels, L-Type; D046911:Macromolecular Substances; D008564:Membrane Potentials / Q000187:drug effects; D016297:Mutagenesis, Site-Directed; D009865:Oocytes / Q000502:physiology; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000187:drug effects; D017384:Sequence Deletion; D014700:Verapamil / Q000031:analogs & derivatives* / Q000494:pharmacology; D014981:Xenopus
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D020746:Calcium Channels, L-Type; D046911:Macromolecular Substances; D011993:Recombinant Fusion Proteins; D014700:Verapamil; C055885:devapamil