Studies on the binding of [3H]amethocaine to rat cerebrocortical membranes.
We have examined the binding of the local anaesthetic agent [3H]amethocaine to rat cerebrocortical membranes. All studies were performed in Tris buffer 50 mmol litre-1 at pH 7.4. Bound and free radioligand were separated by rapid vacuum filtration. [3H]Amethocaine binding at room temperature was dose-dependent and saturable, with mean Kd and Bmax values of 153 (SEM 18) nmol litre-1 and 9.4 (1.6) pmol/mg protein, respectively. [3H]Amethocaine binding was displaced in a dose-dependent manner (pIC50) by unlabelled amethocaine (6.89), procaine (5.20), lignocaine (3.46) and prilocaine (2.81). Ropivacaine and bupivacaine did not produce 50% displacement at the highest concentrations used (10(-4) and 10(-3) mol litre-1, respectively). We examined the nature of the binding site further with a range of ion channel antagonists (nifedipine, verapamil, diltiazem, omega-conotoxin, tetrodotoxin, tetraethylammonium and 4-aminopyridine) and ion channel coupled receptor ligands (L-glutamate, MK801, GABA, glycine and nicotine). With the exception of tetraethylammonium (pIC50 3.07) and 4-aminopyridine (pIC50 3.68), all non-anaesthetic agents failed to displace [3H]amethocaine. Collectively our data suggest that it is unlikely that there is a single target site for all local anaesthetic agents.
Kudo
T
T
University Department of Anaesthesia, Leicester Royal Infirmary.
Kudo
M
M
Hirota
K
K
Lambert
D G
DG
D000779:Anesthetics, Local / Q000378:metabolism*; D000818:Animals; D001667:Binding, Competitive; D002540:Cerebral Cortex / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D007473:Ion Channels / Q000187:drug effects / Q000378:metabolism*; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D013748:Tetracaine / Q000378:metabolism*
D000779:Anesthetics, Local; D007473:Ion Channels; D015221:Potassium Channels; D013748:Tetracaine