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Biomedical subjects

M Huerta

Publications and source records attributed to M Huerta.

At least 55 records · Page 3Linked to original sources
PubMed1998

Field treatment of snakebites in the Israel Defense Forces.

Eight species of venomous snakes capable of inflicting bites dangerous or fatal to humans inhabit the State of Israel. Soldiers in the Israel Defense Forces (IDF) routinely serve under field conditions, and are at greater risk for contact with venomous snakes than are their civilian counterparts. Every year scores of military personnel are bitten by poisonous snakes. The IDF has developed a protocol for field-level treatment of snakebite victims, which we present in this article. Employment of a number of simple therapeutic measures for early treatment of snakebite can prevent or significantly reduce venom-induced morbidity and mortality.

Humans↗
PubMed1997

beta-Adrenergic modulation of Ba2+ currents and K+ contractures in frog slow skeletal muscle fibers.

beta-Adrenergic modulation of the Ba2+ current (IBa) and K+ contracture in slow skeletal muscle fibers of the frog (Rana pipiens) were investigated in intact fibers with the three-microelectrode voltage-clamp technique and isometric tension measurements. Application of epinephrine (10(-6) to 10(-5) M) to the bath increased the amplitude of IBa. This increase was blocked by the beta-antagonist propranolol (3 microM), and a similar increase was observed with the beta-specific agonist isoproterenol (1 microM). Thus the epinephrine effect was mediated mainly by beta-adrenergic receptors. External application of permeable 8-bromoadenosine 3',5'-cyclic monophosphate (0.5 mM) increased the amplitude of both IBa and K+ contractures. The present results suggest that beta-adrenergic modulation of IBa in slow skeletal muscle fibers could reflect a modulation of Ca2+ channels via adenosine 3',5'-cyclic monophosphate (cAMP). cAMP (0.5 mM) also potentiated the K(+)-evoked tension in these slow fibers. The physiological contribution made by the modulation of slow skeletal muscle Ca2+ channels to the increase in tension is still not completely understood.

Adrenergic beta-Agonists↗
PubMed1996

Electrostatic forces as a possible mechanism underlying skeletal muscle contraction.

A possible mechanism is put forward to explain the sliding of thin filaments during muscle contraction. In our model, repulsion due to electrostatic forces is the mechanism which triggers crossbridges to cause the thin filaments to slide. The mechanism proposed could operate regardless of whether the myosin heads rotate or bend, although recent experimental evidence seems to confirm the latter action. In spite of its simplicity, the model prediction of the velocity of sliding of the thin filaments agrees well with experimental values from in vitro motility assays.

Actins↗
PubMed1993

Effects of electrical fields on twitch in skeletal muscle fibers.

The twitch of skeletal muscle fibers was studied under the effects of external electrical fields. Time course of twitches were modified by the presence of electrical fields, while the maximum amplitude of tension remained almost unchanged. It is possible that electrical fields could be acting on the membrane structures of the transverse tubules modifying the excitation-contraction coupling. Alternatively, the alteration of visco-electrical properties of the contractile machinery is proposed as an explanation of this phenomena.

Animals↗
PubMed1992

Caffeine and theophylline contractures in tonic skeletal muscle fibers of the frog.

Caffeine and theophylline evoke maintained tension in tonic skeletal muscle fibers of the frog. Their effects depended upon concentrations ranging from 0.5 to 14 mM. The resting potential of tonic skeletal fiber was unaffected by caffeine or theophylline (4 mM). Caffeine and theophylline contractures have a peak tension followed by a sustained tension, which recovered spontaneously when returned to normal solution. The peak tension and total tension (the area under tension-time curve) were reduced when the fibers were soaked in calcium-free solution. In addition the tension was reduced by calcium channel blockers (cadmium). The sustained tension was increased when external calcium was raised. These results suggest that caffeine and theophylline promote the calcium release from sarcoplasmic reticulum and probably the entry of calcium from external medium.

Animals↗
PubMed1991

Adrenergic modulation of the K+ contractures in tonic skeletal muscle fibers of the frog.

The effects of adrenaline and isoprenaline on K+ contractures of curarized tonic skeletal fibers were investigated. The K+ contractures of tonic fibers have a peak tension followed by a sustained tension. The peak tension and total tension (the tension-time integral--area--of K+ contractures) were increased by adrenaline and isoprenaline. The resting potential of tonic skeletal fibers were unaffected by adrenaline. The calcium channel blocker (cadmium and nifedipine) greatly blocked the effects of adrenaline on the peak and total tension of K+ contractures. On the other hand, the peak and sustained tensions of K+ contractures were greatly reduced in Ca(2+)-free solution, but, the peak tension recovered when the fibers were pre-incubated in adrenaline. It is proposed that adrenergic modulation of tension in tonic skeletal muscle fibers could be related with the modulation of Ca2+ channels and/or Ca2+ release from the sarcoplasmic reticulum.

Animals↗
PubMed1991

Sodium/calcium exchange in tonic skeletal muscle fibers of the frog.

The Na/Ca exchange system was investigated by contractile response to alteration of the extracellular sodium concentration in tonic skeletal muscle fibers of the frog. Contractures were evoked when the extracellular sodium was reduced or withdrawn in the normal solution. This effect was not associated with membrane depolarizations. In the presence of d-tubocurarine, the amplitude and time course of sodium withdrawal contractures were modified, except when sodium was replaced by TEA. When external calcium was omitted from the solution, the tension of sodium withdrawal contracture was greatly reduced. This effect was reversible. These results suggest that Na/Ca exchange is present in the membrane of tonic skeletal muscle fibers of the frog. This conclusion is further supported by the effect of veratridine and strophantidin, which increase the tension of the low-sodium contractures.

Animals↗
PubMed1990

Further analysis of the molecular jet hypothesis during muscle contraction.

We analyse the Molecular Jet-hypothesis proposed by Morel & Bachouchi (1988, J. theor. Biol. 132, 83.). This hypothesis attempts to explain the movement of covaspheres that contain myosin heads attached to actin filaments. This movement occurs during muscle contraction. However, the hypothesis does not predict the velocity of covaspheres correctly. Therefore, we are studying additional aspects of the hypothesis.

Actins↗
PubMed1988

Effect of Ca2+ channel blockers on K+ contractures in twitch fibres of the frog (Rana pipiens).

1. The effects of Ca2+ channel blockers (nifedipine, nitrendipine and diltiazem) were tested on K+ contractures in single muscle fibres of the frog, Rana pipiens. 2. Nifedipine (1 microM) reduced the area under K+ contractures to 24 +/- 9% (4) (100 mM-K+) and 34 +/- 24% (4) (190 mM-K+). Nitrendipine (0.1 microM) reduced the area to 30 +/- 10% (4) (120 mM-K+). The blockade of the contractures was reversible. 3. Diltiazem (1 microM) shortened the first 190 mM-K+ contracture without affecting the peak amplitude. The first contractures, performed at 15-20 min after the removal of diltiazem, were greatly reduced to 29 +/- 14% (4). This effect was reversed after three to five contractures in the absence of the drug. Similar results were obtained with 60 and 100 mM-K+. 4. The resting potential in control saline and after a brief exposure to 120 mM-K+ was not affected by the dihydropyridines and diltiazem. 5. Slow and fast Ca2+ currents were not modified by 1 microM-diltiazem at any stimulation rate or with pre-pulse depolarizations. Diltiazem (50 microM) did not affect the fast Ca2+ current and reduced the slow one to 48 +/- 10% (4). 7. The reduction of K+ contractures by Ca2+ channel blocking agents was not related to a blockade of Ca2+ currents. This can be tentatively explained by interactions of these compounds on membranes sites which regulate the coupling between membrane depolarization and contraction.

Action Potentials↗
PubMed1986

Skeletal muscle Ca2+ channels.

Ca2+ channels are widely distributed among different cell types. We shall describe in this paper kinetic properties of voltage-dependent slow Ca2+ channels in mammalian and frog skeletal muscle fibres. In addition, recent data on a fast-activated Ca2+ channel will be presented. Finally, the possible physiological role of the channel will be considered.

Action Potentials↗
PubMed1986

Calcium action potentials and calcium currents in tonic muscle fibres of the frog (Rana pipiens).

Slow action potentials were evoked in cruralis tonic and twitch fibres of the frog after drastically reducing the Cl- and K+ conductances. Tonic fibres were identified by their electrical characteristics. They had an effective resistance (Reff) of 50 +/- 6 M omega (n = 27) and a membrane time constant (tau m) of 440 +/- 70 ms (n = 8). In twitch fibres Reff = 2.9 +/- 0.3 M omega (n = 16) and tau m = 50 +/- 4 ms (n = 6). In tonic fibres the slow action potential had a threshold of -50 to -60 mV and a peak amplitude of -10 mV. In twitch fibres the slow action potential had a threshold of -40 mV and reached a peak amplitude of +40 mV. The responses were blocked by the addition of Cd2+ (2 mM) or Co2+ (5 mM). These results strongly suggest that Ca2+ is the main carrier of current during the response. Using the three-micro-electrode voltage-clamp technique a slow inward membrane current underlying the Ca2+ potential could be described in tonic muscle fibres. The slow inward current was mainly carried by Ca2+, since it was reduced when external Ca2+ concentration was lowered or when Cd2+ (2 mM) was added. Moreover, Ca2+ was the only cation in the solution that could carry inward current. It had a mean threshold of -60 mV, reached a maximum value at ca. 0 mV, ranged from 24 to 28 microA/cm2 and had a mean reversal potential of +35 mV. In about half of the examined tonic fibres inward current declined with time, only slowly. This can either be explained by there being less contamination by K+ outward current, or by the presence of two types of Ca2+ channels in the tonic fibre membrane.

Action Potentials↗
PubMed1986

Effects of external calcium on potassium contractures in tonic muscle fibers of the frog (Rana pipiens).

K+ contractures of tonic bundles from cruralis muscle of the frog were studied with different K+ concentrations (10-120 mM). K+ contractures had an initial transient phase followed by a sustained tension. The amplitude of the sustained tension diminished with high K+ concentration (80-120 mM). However, in all cases, tension was maintained for several minutes. External Ca2+ reduction practically abolished the sustained phase of the K+ contractures. The initial phase was also reduced and tension spontaneously relaxed. The curve relating the peak tension with log [K+]o, showed that the threshold was not affected but the peak tension was reduced to about 70% in low-Ca2+ saline (0 Ca2+ + 3 mM-Mg2+) and 50% in Ca2+-free saline (1 mM-EGTA + 3 mM-Mg2+). The dependence of the sustained tension on external Ca2+ was further confirmed by Ca2+ withdrawal and re-establishment and/or by Ni2+ substitution for Ca2+ before or during K+ contractures. These results indicate that external Ca2+ had to be continuously present to maintain the tension during K+ contractures and that Ni2+ was not able to restore the normal temporal course of K+ contracture. The sustained phase was diminished by blocking agents of Ca2+ channels, such as nifedipine (1 microM) and diltiazem (1-10 microM). The present results can be explained by a direct control of the Ca2+ currents on K+ contracture or by specific interactions between external Ca2+ and Ca2+-binding sites in the membrane.

Animals↗
PubMed1983

Selective reinnervation of twitch and tonic muscle fibres of the frog.

The electrical properties and innervation of piriformis muscle fibres and the conduction velocities and thresholds of the corresponding motor axons were studied. In normal muscles all fibres clearly fell into the category of twitch or tonic. Tonic muscle fibres were selectively reinnervated by small motor axons after crushing or cutting the piriformis nerve. Twitch fibres were reinnervated by large motor axons. Tonic fibres were also selectively reinnervated by small motor axons when the proximal stump of the piriformis nerve was cut and attached to the caudal end of the muscle. With this procedure the possibility of mechanical guidance by remaining neural sheaths was eliminated. Polyneuronal innervation in twitch fibres in piriformis muscles of normal frogs was 4.7% and in contralateral muscles of operated frogs with the piriformis nerve cut it was 22.6%. Unexpectedly three out of seventeen tonic fibres in contralateral muscles were simultaneously innervated by both small and large motor axons. It is concluded that reinnervation is highly specific for fibre type in frog skeletal muscles.

Animals↗
PubMed1981

Potassium and caffeine contractures in fast and slow muscles of the chicken.

1 K+ contractures, caffeine contractures and electrical properties were studied in slow (posterior latissimus dorsi; p.l.d.) and fast (anterior latissimus dorsi; a.l.d.) chicken muscles. 2. P.l.d. K+ contractures show a transient increase of tension that relaxes spontaneously. Contractures in a.l.d. show an initial component followed by a maintained tension. 3. A.l.d. K+ contractures of similar amplitude and time course were reproduced at 4 min intervals. In p.l.d., the interval needed for full recovery is about 30 min. In Cl-free saline p.l.d. and a.l.d. K+ contractures can be reproduced at 4 min intervals. 4. The time course of repolarization after a short exposure to 160 mM-KCl was much slower in p.l.d. than in a.l.d. In Cl-free saline the time course of repolarization becomes faster in p.l.d. 5. The membrane resistance was not modified in a.l.d. and was increased in p.l.d. by Cl-free saline. The calculated Cl- conductance in p.l.d. was about 70% of the total membrane conductance. 6. In a.l.d., Mn2+, D600 and external Ca2+ reduction greatly diminishes the maintained phase of the K+ contracture leaving the initial phase almost unmodified. Under similar conditions p.l.d. K+ contractures were slightly reduced. 7. P.l.d. caffeine contractures (10-40 mM) were not maintained and they were not modified by Ca-free saline, Cd2+, Co2+, Mn2+ and D600. 8. A.l.d. caffeine contractures (2-15 mM) were maintained and were highly dependent on external Ca2+. In addition they were greatly reduced by Cd2+, Co2+, Mn2 and D600. 9. It is suggested that caffeine contractures of a.l.d. are elicited by a Ca2+ entry into the muscle from the external fluid.

Animals↗
PubMedDate not supplied

High prevalence of calcified silent neurocysticercosis in a rural village of Mexico.

Human neurocysticercosis (NC) is a parasitic disease caused by TAENIA SOLIUM when its larvae lodge in the central nervous system. NC prevalence estimates are obscured by the variable and often asymptomatic clinical picture. While infection depends on exposure, severity is possibly related with various host factors (immunity, genes and gender). This epidemiological study of cranial CT scans in an endemic rural community found that 9.1% of apparently healthy subjects had calcified lesions and were completely asymptomatic. Silent NC cases did not correlate with the exposure factors tested but showed family aggregation and higher rates of positive serology. Thus, NC prevalence may be higher than currently considered and host-related factors appear to be involved in infection and pathogenesis.

Adolescent↗
PubMedDate not supplied

Electrophysiological abnormalities in type 2 diabetic patients with reduced levels of insulin-like growth factor I.

This cross-sectional study investigated electrophysiological abnormalities in type 2 diabetics with normal and reduced insulin-like growth factor I (IGF-I) levels. Sixty patients and 20 non-diabetic controls were included in the study. The fasting serum glucose was measured and IGF-I levels were determined by radioimmunoassay in all patients. Nerve conduction tests were performed in all the study participants on the ulnar nerve and lower extremities. Compared with the controls, all the patients showed a reduction in the peak amplitude of the motor response, 58% showed a reduction in the motor conduction velocity and 55% showed a reduction in the sensory conduction velocity. There was no statistically significant correlation between the electrophysiological changes and the glucose or IGF-I levels. In conclusion, there does not appear to be a correlation between serum glucose or IGF-I levels and electrophysiological abnormalities in patients with type 2 diabetes mellitus.

Adolescent↗