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At least 37 records · Page 2Linked to original sources
PubMed1978

Contractions of skinned cardiac cells elicited by current pulses.

Cardiac muscle fragments with disrupted sarcolemma were prepared by homogenization of mouse ventricles. The preparations exhibited spontaneous contractions of a rate between 3 min-1 and 12 min-1 at 20 degrees C, when they were kept in an appropriate solution. 2. Fragments of about cellular size were attached to two stiff glass microelectrodes, and additional contractions between the spontaneous beats were elicited by current pulses. The duration and intensity of the stimuli were varied to obtain strength-duration curves. Rheobase was in the range of 1.5 muA to 10 muA (no isolation of surrounding bath), chronaxia at 35 degrees C between 30 ms and 80 ms. 3. One microelectrode could be glued to a photodiode-force-transducer for simultaneous recording of contractions and electrical stimulation or potential measurement. Duration of phasic contractions was nearly 1s, force was up to 4muN (20 mN/mm2 of tension).

Animals↗
PubMed1976

Effects of ethanol on compound action potential and refractory periods of toad sciatic nerve.

The action of ethanol on compound action potential, refractory periods and chronaxia are analyzed in 28 isolated sciatic nerves of toads. 85 mM ethanol increases the compound action potential and decreases the refractory periods. 342 and 513 mM ehtanol decrease the compound action potential and increase the absolute and relative refractory periods. These biphasic effects are discussed in relation with changes in Na+ and K+ permeabilities and to the greater sensitivity of thin fibers to the chemicals.

Action Potentials↗
PubMed1976

Differences in the cardiac actions of the calcium antagonists verapamil and nifedipine.

1. It was investigated whether the calcium antagonistic coronary drugs verapamil and nifedipine have similar antiarrhythmic properties. Their effects on functional refractory period and contractile force in the isolated left guinea pig atrium were compared. To assess their influence on myocardial excitability the relation between threshold voltage and pulse duration was studied in the left guinea pig atrium. Furthermore, the influence on AV conduction was investigated in the conscous dog in haemodynamically equieffective dose ranges. 2. Verapamil as well as nifedipine cause a dose-dependent prolongation of the functional refractory period in the isolated left guinea pig atrium. The slope of the dose-response curve of nifedipine is, however, significantly less steep than that of verapamil. Maximum prolongation of refractory period which can be induced by nifedipine is significantly inferior to that occurring after verapamil; under nifedipine this prolongation is, however, accompanied by a significantly greater reduction in contractility. 3. In the isolated left guinea pig atrium the voltage-duration curve is shifted to the right and the chronaxia value is significantly increased by verapamil. Even in the highest dose possible nifedipine has no effect on atrial excitability. 4. In the conscious dog verapamil considerably prolongs AV conduction time whereas a moderate yet dose-dependent shortening of PQ duration is observed with equieffective nifedipine doses regarding the decrease in blood pressure and increase in heart rate. 5. The results indicate that nifedipine does not exert antiarrhythmic effects comparable to those of verapamil.

Animals↗
PubMedDate not supplied

[Biochemical and functional changes in skeletal muscles with electrostimulation].

Electrostimulation of rabbit muscles for 18 days is accompanied by a disturbance in certain biochemical indices and functional state of the muscles. This is confirmed by a decrease in ATP content, intensity of Ca2+ uptake by the sarcoplasmatic reticulum fragments, by a drop in exitability (by the indices of rheobase and chronaxia) as well as by a change in the structure of muscular fibres components, motor axons, motor nerve endings and sciatic nerve stems. Less developed changes are observed when electrostimulation is performed for 5 days and twice for 5 days, including the period of rest. In this case the changes in Atp content and visual deviations in the muscles structure are absent and only the ability of the sarcoplasmatic reticulum fragments to Ca2+ uptake decreases insignificantly and the muscles excitability increases. Administration of ATP and simultaneous electrostimulation for 5 days normalize the disturbed Ca2+ uptake and preserve the higher excitability, that makes it possible to consider this regime of training to be the most acceptable.

Adenosine Triphosphatases↗
PubMedDate not supplied

[Toxicology of 1-4-dioxane].

Toxic parameters of 1-4 dioxan were estimated to be for white rats during 4 hr inhalation LC16 = 40 mg/l LC50 = 46 (42.2 +/- 50.1) mg/l; LC84 = 52 mg/l; for white mice during 2 hr inhalation LC16 = 61 mg/l; LC50 = 65 (61.3 +/- 68.2) mg/l; LC84 = 69.5 mg/l. As a result of single and repeated application, 1-4 dioxan did not induce skin changes, it was rapidly absorbed into the blood, and led to acute poisoning and irritation of the eye mucosa. A 24 hr exposure of white rats to 1-4 dioxan at concentrations of 4 and 20 mg/m3 for 90 days brought about their delayed weight gain, increased activity of glutamate-aspartate and glutamate-alanine transminases, prolonged duration of narcotic sleep, elevated content of protein in the urine, decreased diuresis, changed content of chlorides and altered motor chronaxia. The above concentrations proved to be effective. 1-4 dioxan at a concentrations proved to be effective. 1-4 dioxan at a concentration of 0.5 mg/m3 produced slight threshold changes.

Animals↗