High-affinity binding sites for [3H]saxitoxin are associated with voltage-dependent sodium channels in portal vein smooth muscle.
Saturable, high-affinity binding sites for [3H]saxitoxin were identified in equine portal vein smooth muscle membranes. These sites had a dissociation constant of 0.29 nM and a maximal binding capacity of 115 fmol.mg-1 of protein. A similar dissociation constant was obtained with cells prepared from rat portal vein. Specific binding of [3H]saxitoxin was completely displaced by unlabelled saxitoxin and tetrodotoxin, with inhibition constants of 0.42 and 2.10 nM, respectively. Tetrodotoxin blocked the fast Na+ current in single cells of rat portal vein in a concentration-dependent manner, with an IC50 of 3.15 nM. These results suggest that the high-affinity binding sites for tetrodotoxin and saxitoxin may be associated with voltage-dependent Na+ channels in vascular myocytes.
Mironneau
J
J
Laboratoire de Physiologie Cellulaire et Pharmacologie Moléculaire, INSERM JF 88-13, Bordeaux, France.
Martin
C
C
Arnaudeau
S
S
Jmari
K
K
Rakotoarisoa
L
L
Sayet
I
I
Mironneau
C
C
D029845:Amphibian Proteins; D000818:Animals; D002352:Carrier Proteins / Q000032:analysis*; D006736:Horses; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects; D008566:Membranes / Q000378:metabolism; D009131:Muscle, Smooth, Vascular / Q000737:chemistry*; D011169:Portal Vein / Q000737:chemistry; D051381:Rats; D012530:Saxitoxin / Q000378:metabolism*; D015222:Sodium Channels / Q000737:chemistry*; D013779:Tetrodotoxin / Q000494:pharmacology; D014316:Tritium
D029845:Amphibian Proteins; D002352:Carrier Proteins; D015222:Sodium Channels; C027525:saxitoxin-binding protein, Rana catesbeiana; D014316:Tritium; D012530:Saxitoxin; D013779:Tetrodotoxin