Neurotoxic aminoglycoside antibiotics are potent inhibitors of [125I]-Omega-Conotoxin GVIA binding to guinea-pig cerebral cortex membranes

Abstract

[125I]-Omega-Conotoxin GVIA, a blocker of neuronal (N-type) calcium channels labelled 295 +/- 121 fmol per mg protein of high affinity sites (apparent half-saturation at 1.5 to 2.5 pmol/l) in guinea-pig cerebral cortex membranes. Divalent cations (Cd2+ greater than Ni2+ greater than Co2+ greater than Ca2+ greater than Sr2+ = Ba2+ greater than Mg2+) and La3+ were potent inhibitors of Omega-Conotoxin GVIA binding, whereas monovalent cations (Na+, K+, Li+) were ineffective up to 50 mmol/l. Aminoglycosides (neomycin greater than gentamycin = tobramycin greater than streptomycin greater than amikacin greater than kanamycin) and polymyxin B also inhibited [125I]-Omega-Conotoxin GVIA binding with IC50 values in the mumolar range. All other antibiotics tested were ineffective up to 1 mmol/l. With the exception of polymyxin B, which partially inhibited the binding of the 1,4-dihydropyridine (+)-[3H]PN 200-110 and of (-)-[3H]desmethoxyverapamil, the aminoglycosides and the other antibiotics had no effect on the L-type calcium channel labelling. It is suggested, that inhibition of neurotransmitter release by aminoglycosides is mediated via blockade of the N-type calcium channel to which [125I]-Omega-Conotoxin GVIA binds selectively in a quasi irreversible manner.

Neuropharmacological Characterization of Voltage-Sensitive Calcium Channels: Possible Existence of Neomycin-Sensitive, ω-Conotoxin GVIA- and Dihydropyridines-Resistant Calcium Channels in the Rat Brain

“…The characterization of the specific binding of [125I]w. CTX and [3H]PN200-110 described in the present study is generally consistent with that described in previous stud ies (23,24,30,31). The differences in regional distribu tion in the brain, tissue distribution and pharmacology of…”

Purified omega-conotoxin GVIA receptor of rat brain resembles a dihydropyridine-sensitive L-type calcium channel.

“…Aggregated receptor is seen at top of resolving gel. (27,40,41). EDTA enhances labeling intensity, presumably by removing divalent metals, while calcium and magnesium In initial attempts to purify active CTX receptor, the receptor aggregated and precipitated when applied to various columns.…”

Antinociceptive potency of aminoglycoside antibiotics and magnesium chloride: a comparative study on models of phasic and incisional pain in rats

“…The IC 50 of the antibiotics for both effects was within the micromolar range and the order of potency found was neomycin > gentamicin > streptomycin > kanamycin. Also, the antibiotics were all more potent than magnesium (IC 50 = 3.8 mM) and less potent than wconotoxin GVIA (IC 50 = 21 pM) (15). More recently, Pichler et al (17) found that nanomolar concentrations of antibiotics were effective in inhibiting the binding of [ 125 I]-wconotoxin GVIA to guinea pig cerebellum membranes.…”

“…Magnesium chloride was much less potent than the antibiotics in the tail-flick test and ineffective in the model of incisional pain. Aminoglycoside antibiotics displace the [ 125 I]-w-conotoxin GVIA, but not tritiated Ltype VOCC antagonists from their binding sites in rat brain homogenates (16) or guinea pig brain cortex membranes (15), and inhibit synaptosomal [ 45 Ca] uptake (16). The IC 50 of the antibiotics for both effects was within the micromolar range and the order of potency found was neomycin > gentamicin > streptomycin > kanamycin.…”

“…These drugs act as antagonists on N- (15,16) and P/ Q-type (17) VOCC. A marked similarity between the effects of aminoglycoside antibiotics and magnesium ions, as well as a prompt antagonism of their effects when the extracellular Ca 2+ concentration is increased, have been demonstrated earlier in neuromuscular transmission (for a review, see 11), and confirmed in models of artificial membranes, in rodent cardiac and smooth muscles, and isolated mast cells (for a review, see 18).…”