Do local anaesthetics interact with dihydropyridine binding sites on neuronal L-type Ca2+ channels?
We have examined the interaction of procaine, prilocaine, lignocaine, bupivacaine, amylocaine and R(+) and S(-) ropivacaine with L-type voltage-sensitive Ca2+ channels in rat cerebrocortical membranes. Membranes were prepared in Tris HCl 50 mmol litre-1, pH 7.4, by homogenization and centrifugation. Binding assays were performed in 1-ml volumes of Tris HCl 50 mmol litre-1, pH 7.4, for 90 min at room temperature using approximately 200 micrograms of protein. Non-specific binding was defined in the presence of nifedipine 10(-5) mol litre-1, and bound and free radioactivity were separated by vacuum filtration. The effects of local anaesthetics were determined by displacement of [3H]PN200-110 (approximately 0.2 nmol litre-1), a radiolabelled 1,4- dihydropyridine (DHP) L-channel antagonist. The concentration of displacer producing 50% displacement was corrected for the competing mass of [3H]PN200-110 to yield the affinity constant, K50. All local anaesthetics displaced [3H]PN200-110 in a dose-dependent manner with a rank order potency of (K50, mmol litre-1) bupivacaine (0.48), amylocaine (0.74), lignocaine (1.09), prilocaine (2.06) and procaine (2.09). Ropivacaine enantiomers did not show stereo-selective displacement, with K50 values of 0.99 and 0.92 mmol litre-1 for R(+) and S(-) ropivacaine, respectively. There was a significant correlation between pK50 and p (octanol:buffer partition coefficient) (r2 = 0.872, P = 0.020), pK50 and p (local anaesthetic potency) (r2 = 0.816, P = 0.036), pK50 and p (relative conduction blocking potency) (r2 = 0.843, P = 0.028) and between pK50 and p (IC50 for inhibition of cardiac output) (r2 = 0.897, P = 0.015). These data suggest that DHP binding sites may be involved in both the mechanism of local anaesthesia and the cardiotoxicity of these agents.
Hirota
K
K
Department of Anaesthesia, Leicester Royal Infirmary.
Browne
T
T
Appadu
B L
BL
Lambert
D G
DG
D000779:Anesthetics, Local / Q000378:metabolism*; D000818:Animals; D001667:Binding, Competitive; D015220:Calcium Channels / Q000378:metabolism*; D020746:Calcium Channels, L-Type; D002540:Cerebral Cortex / Q000378:metabolism*; D046508:Culture Techniques; D004305:Dose-Response Relationship, Drug; D005260:Female; D009474:Neurons / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar
D000779:Anesthetics, Local; D015220:Calcium Channels; D020746:Calcium Channels, L-Type