Ketamine blockade of voltage-gated sodium channels: evidence for a shared receptor site with local anesthetics.

BACKGROUND: The general anesthetic ketamine is known to be an N-methyl-D-aspartate receptor blocker. Although ketamine also blocks voltage-gated sodium channels in a local anesthetic-like fashion, little information exists on the molecular pharmacology of this interaction. We measured the effects of ketamine on sodium channels. METHODS: Wild-type and mutant (F1579A) recombinant rat skeletal muscle sodium channels were expressed in Xenopus oocytes. The F1579A amino acid substitution site is part of the intrapore local anesthetic receptor. The effect of ketamine was measured in oocytes expressing wild-type or mutant sodium channels using two-electrode voltage clamp. RESULTS: Ketamine blocked sodium channels in a local anesthetic-like fashion, exhibiting tonic blockade (concentration for half-maximal inhibition [IC50] = 0.8 mm), phasic blockade (IC50 = 2.3 mm), and leftward shift of the steady-state inactivation; the parameters of these actions were strongly modified by alteration of the intrapore local anesthetic binding site (IC50 = 2.1 mm and IC50 = 10.3 mm for tonic and phasic blockade, respectively). Compared with lidocaine, ketamine showed greater tonic inhibition but less phasic blockade. CONCLUSIONS: Ketamine interacts with sodium channels in a local anesthetic-like fashion, including sharing a binding site with commonly used clinical local anesthetics.

Meperidine and lidocaine block of recombinant voltage-dependent Na+ channels: evidence that meperidine is a local anesthetic.

BACKGROUND: The opioid meperidine induces spinal anesthesia and blocks nerve action potentials, suggesting it is a local anesthetic. However, whether it produces effective clinical local anesthesia in peripheral nerves remains unclear. Classification as a local anesthetic requires clinical local anesthesia but also blockade of voltage-dependent Na+ channels with characteristic features (tonic and phasic blockade and a negative shift in the voltage-dependence of steady-state inactivation) involving an intrapore receptor. The authors tested for these molecular pharmacologic features to explore whether meperidine is a local anesthetic. METHODS: The authors studied rat skeletal muscle mu1 (RSkM1) voltage-dependent Na+ channels or a mutant form heterologously coexpressed with rat brain Na+ channel accessory beta1, subunit in Xenopus oocytes. Polymerase chain reaction was used for mutagenesis, and mutations were confirmed by sequencing. Na+ currents were measured using a two-microelectrode voltage clamp. Meperidine and the commonly used local anesthetic lidocaine were applied to oocytes in saline solution at room temperature. RESULTS: Meperidine and lidocaine produced tonic current inhibition with comparable concentration dependence. Meperidine caused phasic current inhibition in which the concentration-response relationship was shifted to fivefold greater concentration relative to lidocaine. Meperidine and lidocaine negatively shifted the voltage dependence of steady-state inactivation. Mutation of a putative local anesthetic receptor reduced phasic inhibition by meperidine and lidocaine and tonic inhibition by lidocaine, but not meperidine tonic inhibition. CONCLUSIONS: Meperidine blocks Na+ channels with molecular pharmacologic features of a local anesthetic. The findings support classification of meperidine as a local anesthetic but with less overall potency than lidocaine.

Effects of zidovudine use during pregnancy on resistance and vertical transmission of human immunodeficiency virus type 1.

The resistance of human immunodeficiency virus type 1 (HIV-1) to zidovudine and the vertical transmission of the virus were assessed among all 62 HIV-1-infected pregnant women identified prior to delivery at one institution. HIV-1 was transmitted to infants from 11 (26%) of 42 women who did not receive oral zidovudine but from only 1 of 20 women given such treatment (P = .04). Isolates of HIV-1 from 16 of the 20 zidovudine-treated women were available. Twelve of 16 isolates were wild-type for pol codons 41, 67, 70, 215, and 219; two (one susceptible and one moderately resistant to zidovudine) had mutations at codon 70; and two (both highly resistant to zidovudine) had mutations at codons 41 and 215. The virus was vertically transmitted from a woman infected with one of the highly resistant strains, and the infant's isolate was highly resistant to zidovudine. These limited data suggest that maternal treatment with oral zidovudine reduces the rate of vertical transmission of HIV-1 but that vertical transmission of virus resistant to zidovudine can occur.

Specific, sensitive, and rapid assay for human immunodeficiency virus type 1 pol mutations associated with resistance to zidovudine and didanosine.

The effectiveness of antiretroviral therapy may be limited by the development of human immunodeficiency virus type 1 (HIV-1) resistance. Monitoring for resistance will perhaps allow changes in therapy prior to deterioration in the patient's clinical or immunologic status. Our objective was to develop a rapid, specific, and sensitive genotypic assay for HIV-1 resistance to zidovudine (ZDV) and didanosine (ddI) which is simple to perform. In our assay the DNA of HIV-1 pol was amplified by PCR using two sets of nested oligonucleotide primers. Mutations of reverse transcriptase (RT) encoding amino acids (aa) 74 and 41, 70, and 215 which have been associated with HIV-1 resistance to ddI and ZDV, respectively, were detected with a ligase detection reaction (LDR) and indicated colorimetrically. The RT genotypes of 35 patient specimens (140 codons) blindly assessed for these mutations were in agreement by PCR-LDR and by dideoxynucleotide sequencing. To evaluate the limits of the assay, other specimens with mutations close to the ligation site were evaluated by PCR-LDR. The assay was sensitive and specific for all specimens except when mutations occurred within 2 bases on either side of the ligation site. In summary, this PCR-LDR assay specifically, sensitively, and rapidly detected pol mutations (RT aa 74, 41, 70, and 215) associated with HIV-1 resistance to ddI and ZDV.

Measurement of tachykinin-induced salivation in conscious rats.

A method of quantitatively measuring tachykinin-induced salivation in conscious, male, Sprague-Dawley rats is described. Salivation is quantified by determining the weight of a preweighed, absorbant foam cube after it has been used to swab the oral cavity of a tachykinin challenged rat. Salivation is induced by intravenous (i.v.) injection of sialogogues (microgram/kg) via the lateral tail vein. Measurements are made immediately after injection. Substance P (Sub.P), Sar9, Met (O2) 11Substance P (Sar9 Sub.P), a selective neurokinin (NK) 1 receptor agonist, Physalaemin and Eledoisin are equipotent sialogogues as determined by this method. Neurokinin A (NKA), the endogenous NK2 receptor agonist, is 0.27 (0.14-0.46) times as potent as Sub. P, while (Suc-[Asp6, MePhe8]Substance P(6-11), (senktide), a selective NK3 receptor agonist, only induced salivation at 300 microgram/kg. Acetylcholine (Ach) is only 0.006 (0.002-0.012) times as potent as Sub.P. Treatment with the neurokinin antagonist [D-Arg1, D-Trp7,9 Leu11]-Substance P (spantide) dose-dependently inhibits Sub. P stimulated salivation. Atropine dose-dependently inhibits Ach induced salivation but is inactive against Sub.P-induced salivation. These data are consistent with literature values and indicate that this method provides a simple, quantitative model, free of any possible anesthetic side effects, for the measurement of neurokinin stimulated salivation and the assessment of potential neurokinin antagonists in vivo.

AHR-10037, a non-steroidal anti-inflammatory compound of low gastric toxicity.

AHR-10037 is an anti-inflammatory compound possessing analgesic and antipyretic properties and a high therapeutic index. AHR-10037 was comparable to indomethacin in suppressing acute (Evans blue-carrageenan pleural effusion) and chronic (adjuvant-induced arthritis) inflammation. There was a delayed onset of antipyresis (yeast-induced hyperthermia in rats), analgesia (acetylcholine-induced abdominal constriction in mice) and inhibition of caster oil-induced diarrhea in rats. Antipyresis occurred 3 hours after administration of AHR-10037, 4 mg/kg, PO. vs 1 hour after administration of acetylsalicylic acid, 100 mg/kg, PO; maximum analgesic activity (ED50 = 4.1 mg/kg) occurred at 4 hours. AHR-10037 was inferior to indomethacin in suppressing castor oil-induced diarrhea in rats. The therapeutic index of AHR-10037 (relating acute anti-inflammatory potency to gastric toxicity potency relative to indomethacin) ranged from 56-91. The pharmacological profile suggests that AHR-10037 is a prodrug converted in vivo to a cyclooxygenase inhibitor.

The effect of calcium channel blockers and calmodulin inhibitors on the macrophage factor-stimulated synthesis of collagenase by rabbit chondrocytes.

Macrophages and monocytes secrete a factor(s) which can stimulate the synthesis of collagenase in synovial cells and in chondrocytes. Incubation of rabbit chondrocytes with macrophage conditioned medium (MCM) and with the calcium channel blockers, nifedipine, verapamil or diltiazem (up to 200 microM) had no effect on collagenase synthesis. However, TMB-8 (8-[N,N-diethylamino]-octyl 3,4,5-trimethoxybenzoate hydrochloride), an inhibitor of internal calcium movement, did inhibit the process with an IC50 of approximately 130 microM. The calmodulin antagonists, trifluoperazine, chlorpromazine and calmidazolium (R-24571) were effective inhibitors of the process with IC50's of 40 microM, 18 microM and 3.5 microM, respectively. Collagenase activity itself was not affected by these agents. The data suggests that calmodulin and/or internal calcium movement may play a role in the macrophage factor-stimulated synthesis of collagenase in rabbit chondrocytes.

The topical anti-inflammatory and analgesic properties of bromfenac in rodents.

Bromfenac [2-amino-3-(4-bromobenzoyl)benzeneacetic acid sodium salt sesquihydrate] is an anti-inflammatory/analgesic agent that possesses potent topical activity in rats, guinea pigs, and mice. In rat models of acute (carrageenan paw edema) and chronic (adjuvant arthritis) inflammation, preparations of bromfenac at concentrations as low as 0.01-0.32% (0.01-0.32 mg bromfenac) produced significant anti-inflammatory activity when applied to the injected paw or to the backs of rats. In the acute paw edema test, topical bromfenac was more potent than indomethacin or hydrocortisone and about as active as triamcinolone acetonide. Bromfenac, at concentrations of 0.1-0.32%, showed topical analgesic activity in the acetylcholine-induced abdominal constriction test in mice. In this test, bromfenac was more potent than indomethacin (24.9X), more potent than ketoprofen (approximately 14.9X), and superior to piroxicam. In the guinea pig UV-erythema test, bromfenac was active (26.1X indomethacin) when applied to the UV-exposed site, but not when applied away from the site. The results suggest that bromfenac has activity topically because of a local and a systemic effect. Test results obtained with a long (4-7 hr) pretreatment time (paw edema, adjuvant arthritis, abdominal constriction) are due in great part to a systemic effect of topically applied bromfenac, while the UV-erythema test (1-hr treatment time) clearly indicates a local effect.

The analgesic and antiinflammatory activity and pharmacologic properties of bromfenac.

Bromfenac sodium (2-amino-3-(4-bromobenzoyl)benzeneacetic acid sodium salt sesquihydrate, AHR-10282B) is a potent long-acting, peripheral, analgesic compound possessing antiinflammatory, antipyretic, and prostaglandin synthetase-inhibiting properties. In the acetylcholine abdominal constriction assay in mice, bromfenac (bromfenac sodium) by the oral route at pretreatment times of 10, 20 and 300 min was respectively 3.7, 6.5 and 2.9 times more potent than zomepirac and 3.4, 6.6., and 44.2 times more potent than suprofen. In dogs bromfenac when given orally was 5.8 times more potent than zomepirac in blocking the nociceptive response to bradykinin. Naloxone did not alter the analgesic properties of bromfenac in mice; and after repeated administration, tolerance to analgesia did not develop. Bromfenac, given orally, was more potent than indometacin in suppressing acute (7.5-20 times) and chronic (3.8 times) inflammation. The gastric and intestinal toxicity potencies of bromfenac, given orally, were comparable with and 1.8 times more potent than indometacin, respectively. Bromfenac was 6.1 to 32.8 times more potent than indometacin in inhibiting the formation of prostaglandin E2 and F2 alpha from microsomes of bovine seminal vesicles, rabbit uteri, and rabbit renal medullae; but it did not block the direct action of prostaglandin E1 (abdominal constriction) and prostaglandin F2 alpha (contraction of the uterus). Bromfenac produced no unwanted central nervous system, cardiovascular, or autonomic effects.