Characterization of (/sup 3/H)nifedipine binding to intact vascular smooth muscle cells

Journal Article · Fri Jan 01 04:00:00 EST 1988 · Am. J. Physiol.; (United States)

OSTI ID:5481594

Sumimoto, K; Hirata, M; Kuriyama, H

Specific binding of the dihydropyridine Ca2+ antagonist (/sup 3/H)nifedipine to dispersed smooth muscle cells of the porcine coronary artery was investigated and the findings were compared with the binding to microsomes of smooth muscles. Specific binding to intact cells was saturable and reversible. The dissociation constant was 1.93 +/- 0.42 nM and the maximal binding capacity was 59.6 +/- 12.4 fmol/10(6) cells, as assessed by Scatchard analysis of the equilibrium binding at 25 degrees C. The Kd value with intact cells was slightly higher than that observed with microsomes. Specific binding of (/sup 3/H)nifedipine to intact cells was completely displaced by unlabeled dihydropyridine derivatives. Among other Ca2+ antagonists, verapamil and d-cis-diltiazem partially and flunarizine completely inhibited the binding. In the case of microsomes, d-cis-diltiazem stimulated the binding of (/sup 3/H)nifedipine. These results suggest that there may be multiple binding sites for different subclasses of Ca2+ antagonists. Polyvalent cations had no effect on the binding to intact cells. In the case of ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA)-treated microsomes, the addition of CaCl/sub 2/ and BaCl/sub 2/ increased the Bmax, but the Kd value remained unchanged. MnCl/sub 2/ and CdCl/sub 2/ had stimulatory or inhibitory effects, depending on the concentrations, whereas LaCl3 had no effect. The effect of membrane depolarization on the binding was also examined. When the intact cells were incubated in high (K+)o solution for 60 min, the Kd was lowered to 1.4 nM from the control value of 2.0 nM, thereby indicating that (/sup 3/H)nifedipine binds to Ca2+ channels, with a higher affinity, at depolarized states.

• Research Organization: Kyushu Univ., Fukuoka, Japan
• OSTI ID: 5481594
• Journal Information: Am. J. Physiol.; (United States), Journal Name: Am. J. Physiol.; (United States) Vol. 254; ISSN AJPHA
• Country of Publication: United States
• Language: English

Related Subjects

550201* -- Biochemistry-- Tracer Techniques
59 BASIC BIOLOGICAL SCIENCES
ALKALINE EARTH METAL COMPOUNDS
ANIMALS
BIOCHEMICAL REACTION KINETICS
CALCIUM COMPOUNDS
CARDIOVASCULAR AGENTS
CATIONS
CELL CONSTITUENTS
CELL MEMBRANES
CHARGED PARTICLES
DOMESTIC ANIMALS
DRUGS
ELECTROPHYSIOLOGY
IONS
ISOTOPE APPLICATIONS
KINETICS
LABELLED COMPOUNDS
MAMMALS
MEMBRANE PROTEINS
MEMBRANES
MICROSOMES
MUSCLES
ORGANIC COMPOUNDS
ORGANOIDS
PHYSIOLOGY
PROTEINS
REACTION KINETICS
RECEPTORS
SWINE
TRACER TECHNIQUES
TRITIUM COMPOUNDS
VASODILATORS
VERTEBRATES