Decamethonium in depolarized muscle and the effects of tubocurarine

1. In rat diaphragms immersed in solution containing 5 mM potassium the maximum uptake of labelled decamethonium was found at the end-plate region. In muscles depolarized in solution containing potassium methyl sulphate the uptake was reduced but a peak concentration at the end-plate region was still demonstrated.2. The uptake of labelled decamethonium increased steadily with time and was interpreted in terms of the entry of decamethonium into the fibres. The permeability at 10-100 muM was similar to that of sodium.3. The uptake of decamethonium at the end-plate region was dependent on the concentration. At low values the uptake in depolarized muscle was uniform along the fibres. Increase in concentration produced a peak at the end-plate region. This was interpreted as a change in permeability such that half the maximum effect was present at a concentration of approximately 5 muM.4. At high concentrations the influx showed saturation and carrier-like kinetics with a half-saturation concentration of 400 muM.5. Tubocurarine inhibited the peak uptake in depolarized diaphragm. The results were consistent with competitive inhibition with an inhibitory constant of 0.07 muM.6. Acetylcholine in high concentration also inhibited the uptake of decamethonium in the end-plate region of depolarized muscle.     

Tension and cycb'c GMP changes in potassium depolarized rabbit colon muscle

Potassium depolarization of rabbit colon muscle elicited a contraction consisting of 2 distinct phases, an initial rapid phasic contraction and a tonic contracture. The tonic contraction was, in contrast to the phasic contraction, dependent on the extracellular calcium for its development. There was a correlation between the tension development and the increase of the cyclic GMP level in the K⁺-depolarized muscle. Experimental conditions which abolished the tonic contracture, viz glucose omission and treatment with Ca²⁺-antagonists (verapamil, SKF 525A) also inhibited the cyclic GMP response. The changes of the cyclic GMP levels were Ca²⁺-dependent. K⁺-ions also changed the cyclic AMP content an effect which was atropine sensitive. From the experimental data obtained in this investigation we suggest that the co-variation of the tension and the cyclic GMP level in the depolarized colon muscle might depend on oscillations in a common intracellular factor, probably Ca²⁺.     

Tension and cyclic GMP changes in potassium depolarized rabbit colon muscle.

Potassium depolarization of rabbit colon muscle elicited a contraction consisting of 2 distinct phases, an initial rapid phasic contraction and a tonic contracture. The tonic contraction was, in contrast to the phasic contraction, dependent on the extracellular calcium for its development. There was a correlation between the tension development and the increase of the cyclic GMP level in the K+-depolarized muscle. Experimental conditions which abolished the tonic contracture, viz glucose omission and treatment with Ca2+-antagonists (verapamil, SKF 525A) also inhibited the cyclic GMP response. The changes of the cyclic GMP levels were Ca2+-dependent. K+-ions also changes the cyclic AMP content an effect which was atropine sensitive. From the experimental data obtained in this investigation we suggest that the co-variation of the tension and the cyclic GMP level in the depolarized colon muscle might depend on oscillations in a common intracellular factor, probably Ca2+.     

Long-lasting resistance to haloperidol-induced catalepsy in male rats chronically treated with caffeine

Chronic caffeine consumption has been inversely associated with the risk of developing Parkinson's disease. Here we assessed whether chronic caffeine treatment increases the resistance of male Wistar rats to haloperidol (1 mg/kg, s.c.)-induced catalepsy, measured in the bar test at 15 min intervals during 3 h. Caffeine (5 mg/kg/day) was delivered for 6 months via drinking water. Control rats received only tap water. Treatments began when animals were 3–4 months old. In order to unveil long-lasting catalepsy refractoriness not attributable to the presence of caffeine in the brains of rats, they were evaluated from day 18 to day 27 after caffeine withdrawal, a time that is far in excess for the full excretion of a caffeine dose in this species. The average cataleptic immobility measured in caffeine-treated rats (n = 23) was 1148 ± 140 s, a value 34 ± 8% lower than that recorded in control animals (n = 20), whose mean immobility was 1736 ± 137 s (P = 0.0026, t-test). The percentage of catalepsy reduction measured in caffeine-treated rats evaluated on days 18–20 after caffeine discontinuation (−32 ± 13%, n = 12, P < 0.05) was comparable to the catalepsy decrease recorded in those animals tested on days 21–27 (−36 ± 10%, n = 11, P < 0.02), a finding compatible with the notion that the effect was indeed mediated by enduring changes of brain functioning and not by the physical presence of caffeine or its metabolites. Caffeine-treated rats also had higher catalepsy latency scores compared with control rats (P < 0.01, U-test). The present findings show that chronic consumption of caffeine produces perdurable resistance to catalepsy induced by dopamine receptor blockade, possibly through enhancement of dopamine transmission, giving further support to the epidemiological results indicating that prolonged caffeine consumption affords neuroprotection against Parkinson's disease.     

Sodium nitrate alleviates functional muscle ischaemia in patients with Becker muscular dystrophy

AbstractBecker muscular dystrophy (BMD) is a progressive X‐linked muscle wasting disease for which there is no treatment. BMD is caused by in‐frame mutations in the gene encoding dystrophin, a structural cytoskeletal protein that also targets other proteins to the sarcolemma. Among these is neuronal nitric oxide synthase mu (nNOSμ), which requires specific spectrin‐like repeats (SR16/17) in dystrophin''s rod domain and the adaptor protein α‐syntrophin for sarcolemmal targeting. When healthy skeletal muscle is exercised, sarcolemmal nNOSμ‐derived nitric oxide (NO) attenuates α‐adrenergic vasoconstriction, thus optimizing perfusion. In the mdx mouse model of dystrophinopathy, this protective mechanism (functional sympatholysis) is defective, resulting in functional muscle ischaemia. Treatment with a NO‐donating non‐steroidal anti‐inflammatory drug (NSAID) alleviates this ischaemia and improves the murine dystrophic phenotype. In the present study, we report that, in 13 men with BMD, sympatholysis is defective mainly in patients whose mutations disrupt sarcolemmal targeting of nNOSμ, with the vasoconstrictor response measured as a decrease in muscle oxygenation (near infrared spectroscopy) to reflex sympathetic activation. Then, in a single‐arm, open‐label trial in 11 BMD patients and a double‐blind, placebo‐controlled cross‐over trial in six patients, we show that acute treatment with oral sodium nitrate, an inorganic NO donor without a NSIAD moiety, restores sympatholysis and improves post‐exercise hyperaemia (Doppler ultrasound). By contrast, sodium nitrate improves neither sympatholysis, nor hyperaemia in healthy controls. Thus, a simple NO donor recapitulates the vasoregulatory actions of sarcolemmal nNOS in BMD patients, and constitutes a putative novel therapy for this disease.

Abbreviations

BMD

Becker muscular dystrophy

deoxyHb

deoxyhaemoglobin

deoxyMb

deoxymyoglobin

DMD

Duchenne muscular dystrophy

LBNP

lower body negative pressure

MVC

maximal voluntary contraction

NIRS

near infrared spectroscopy

NO

nitric oxide

NO₂⁻

nitrite

NO₃⁻

nitrate

nNOSμ

neuronal nitric oxide synthase mu

NSAID

non‐steroidal anti‐inflammatory drug

PDE5

phosphodiesterase 5

TLS

total labile signal

     

Influence of [H+]o on42K-exchange in sartorius muscle treated with barium or 9-aminoacridine

Summary ⁴²K-exchange in resting frog sartorius muscle was altered markedly by changes in [H⁺]_o. Elevated [H⁺]_o depressed the rate of⁴²K-uptake and increased the rate constant of⁴²K-loss. In addition, [K⁺]_i was decreased. By contrast, elevated [H⁺]_o depressed both the uptake and rate of loss of²²Na and had no effect on [Na⁺]_i. Similarly, [Ca⁺⁺]_i and [Mg⁺⁺]_i were unaffected by changes in [H⁺]_o. The blockade of⁴²K-exchange by 9-aminoacridine (9AA), but not that caused by Ba⁺⁺, was sensitive to changes in [H⁺]_o was resistant to blockade by 9AA. There was a good correspondence between the uptake and loss of 9AA by muscles as a function of [H⁺]_o and the sensitivity of⁴²K-exchange to blockade by 9AA. The uptake of 9AA was retarded and the loss of 9AA accelerated by elevation of [H⁺]_o.Supported by research grants NS-07540 and NS-09148 from Institute of Neurological Diseases and Stroke, National Institutes of Health, Bethesda, Maryland.     

Cardiotoxicity of Ma Huang/caffeine or ephedrine/caffeine in a rodent model system

Ma Huang (equivalent to 0, 12.5, 25, or 50 mg/kg ephedrine) or ephedrine (0, 6.25, 12.5, 25 mg/kg) were administered as one bolus oral dose to male F344 rats with and without caffeine. The herbal medicine Ma Huang (ephedra) in combination with caffeine caused rapid clinical signs of toxicity including salivation, hyperactivity, ataxia, and eventually lethargy, and failure to respond to stimuli. When this syndrome of clinical signs emerged, animals were moribund sacrificed, and a histological analysis for heart lesions performed. Cardiotoxicity included hemorrhage, necrosis, and degeneration in the ventricles or interventricular septum within 2-4 hours after treatment with Ma Huang (ephedra)/caffeine or ephedrine (the principal active component in Ma Huang)/caffeine. There was a steep dose response curve for cardiotoxicity with minimal toxicity seen at levels of Ma Huang (equivalent to 12.5 mg/kg ephedrine) with caffeine. However, cardiotoxic lesions occurred in 28% of animals with Ma Huang dosages equivalent to 25 mg/kg ephedrine with 15 or 30 mg/kg caffeine, and in 90% of animals at Ma Huang exposures equivalent to 50 mg/kg ephedrine with 15 or 30 mg/kg caffeine. Cardiotoxic lesions occurred in 47% of animals in the 25 mg/kg ephedrine groups with caffeine at 7.25, 15, or 30 mg/kg. There was no statistical difference in the occurrence of cardiotoxic lesions when 15 or 30 mg/kg caffeine was combined with Ma Huang equivalent to 25 or 50 mg/kg ephedrine; likewise there was no statistical difference in the occurrence of cardiotoxic lesions when 7.25, 15, or 30 mg/kg caffeine was combined with 25 mg/kg ephedrine. These results show that the cardiotoxic effects of the herbal medicine, Ma Huang, are similar to that of ephedrine, the principal active ingredient in the herbal medicine. The combination of Ma Huang or ephedrine with caffeine enhanced the cardiotoxicity over that with the herbal medicine or the active ingredient alone.