Action potentials of the rabbit, guinea pig, dog and albino rat working ventricular myocardium under interpolated extrasystole conditions during postnatal ontogenesis

Experiments were carried out on the working myocardium of the right heart ventricle of newborn and adult rabbits, guinea-pigs, dogs and albino rats. In the dog, the guinea-pig and the rabbit, after ten action potentials (AP) elicited with 1 Hz frequency we always interpolated an extrasystole at an interval (TE) of 100-900 ms. In albino rats we used a basic frequency of 2 Hz and a TE of 30-370 ms from the last regular AP. Using glass microelectrodes, we recorded the extrasystolic AP (EAP) and the next subsequent AP (2AP). The results were evaluated by constructing graphs of the correlations of the duration of the plateau phase (D0) to TE and of the duration of repolarization to -60 mV level (D60) to the TE. In the myocardium of newborn rabbits, guinea-pigs and dogs, with short TE both D0 and D60 of the EAP are shorter than in the steady state (SS), while for the 2AP the same parameters are influenced only a little. As the TE lengthens, the EAP gradually acquire a length corresponding more to the SS. With TE longer than half the duration of the cycle in the steady state the EAP return to normal, while the 2AP become shorter. The effect of extrasystole on the rat EAP and 2AP diminished with advancing age. In the myocardium of adult rabbits and adult guinea-pigs, and slightly in the myocardium of adult dogs and newborn rats, we observed that the duration of the EAP, with certain TE, was greater than in the steady state.(ABSTRACT TRUNCATED AT 250 WORDS)     

A microcomputer-based analyser for evaluation of contractile properties of a cardiac muscle

A computer controlled equipment is described for computer analysis of isometric contractions of cardiac muscle by different modes of excitation. Both the method and the programme are presented. The following parameters are analysed: half and full contraction time, half relaxation time, maximum force developed during contraction, maximum rate of force development. The same computer is simultaneously used for controlling the stimulation.     

Histochemical study of calcium on T-tubule membranes and in the sarcoplasmic reticulum, in frog twitch muscle fibres at rest and during activity

The trigger calcium hypothesis of signal transmission between T-tubules and terminal cisternae (TC) of the sarcoplasmic reticulum (SR) in twitch muscle fibres implies the presence of calcium along T-tubule membranes at rest and its release upon excitation. To test this hypothesis, calcium was immobilised using a fixing and precipitating solution of glutaraldehyde in phosphate buffer at pH 8.0 and the calcium was substituted for by lead. Simultaneous tension recordings revealed the occurrence of contractions or a burst of twitches upon perfusion with the fixative. Procaine or tetrodotoxin (TTX) was used to inhibit this activity. In fibres without fixative-induced activity, precipitates were observed along T-tubules and in adjoining parts of TC. In activated fibres, tubular and TC precipitates were absent. These results are consistent with the trigger calcium hypothesis. In fibres activated by depolarisation, calcium returned to TC after passing successively through different parts of the SR.