Desmethoxyverapamil-sensitive calcium channels in rat portal vein smooth muscle.
The whole-cell patch clamp technique was used to analyze the properties of the phenylalkylamine-sensitive calcium channels in smooth muscle cells isolated from the portal vein. (-)-D888 dose dependently inhibited the calcium current elicited from a holding potential of -40 mV (IC50 = 1.3 nM) in a frequency-dependent manner. No voltage dependence of the inhibition was noted. Independent high- and low-affinity binding sites for (-)-[3H]D888 were identified. Calcium entry blockers such as (-)-D888, d-cis-diltiazem and nicardipine completely or partially antagonized the (-)-[3H]D888 binding at both types of sites. The properties of this cross-inhibition suggest that phenylalkylamines and d-cis-diltiazem bind at common sites in vascular smooth muscles whereas dihydropyridines bind at distinct sites which are allosterically coupled to the phenylalkylamine sites. As the IC50 for (-)-D888 found from electrophysiological experiments is not identical to the equilibrium dissociation constants for the high- and low-affinity sites found from binding data (0.47 and 50 nM, respectively), it is suggested that binding of (-)-D888 to both high- and low-affinity sites may be involved in the inhibitory effect of (-)-D888 on calcium channels. Furthermore, these two different binding sites may correspond to two different subtypes of phenylalkylamine-sensitive calcium channels in smooth muscle cells.
Loirand
G
G
Laboratoire de Physiologie Cellulaire et Pharmacologie Moléculaire, INSERM JF 88-13, Université de Bordeaux II, France.
Dacquet
C
C
Pacaud
P
P
Rakotoarisoa
L
L
Sayet
I
I
Mironneau
C
C
Mironneau
J
J
D000818:Animals; D015220:Calcium Channels / Q000187:drug effects*; D004110:Diltiazem / Q000494:pharmacology; D066298:In Vitro Techniques; D008566:Membranes / Q000187:drug effects / Q000378:metabolism; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism*; D009529:Nicardipine / Q000494:pharmacology; D011169:Portal Vein / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D014700:Verapamil / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology
D015220:Calcium Channels; C043184:4-desmethoxyverapamil; D014700:Verapamil; D009529:Nicardipine; D004110:Diltiazem