[Effect of the rest interval on the contractile activity of the myocardium]. / Vliianie intervala pokoia na sokratitel'nuiu aktivnost' miokarda.

Isolated strips of the heart auricles and ventricles of frogs at high stimulation frequencies revealed rest potentiation which depended both on the stimulation rhythm and on the duration of rest interval. Amphibians as well as warm-blooded animals and fish seem to display a possibility of Ca++ entering a cell during the period of rest via non-electrogenic calcium canals, but in amphibians this mechanism of the myocardium activation is compansatory, rather.

[Analysis of chrono-inotropy of the myocardium in poikilothermic animals]. / K analizu khrono-inotropii miokarda poikilotermykh zhivotnykh.

Chrono-ionotropic interrelationships were studied in isolated strips of the myocardium of poikilothermous animals (frogs and fishes) in conditions of either stationary or transitional regimens of stimulation. In the stationary regimen, the rhythm-strength relation is simple and corresponds to a parabolic curve. While changing the lesser frequency of stimulation for greater one, both the positive and negative transitional abbreviating stirs were observed, in contrast to literature references. The phenomena of positive and negative transitional stairs were concluded to be unrelated to species while being a general biological form of the myocardium response to change of the stimulation rhythm.

[The "staircase" phenomenon in the myocardial activity of fishes and amphibians]. / O fenomene "lestnitsy" v deiatel'nosti miokarda ryb i amfibii.

Studies have been made on chrono- and inotropic effects in the heart of the frog Rana temporaria and fishes Silurus glanis and Cyprinus carpio during stationary and transitional stimulation. In contrast to data in the literature, no interspecific differences were found in changes of the amplitude of cardiac contractions induced by changes in rhythmic stimulation.

[Action potentials of the heart atria and ventricles of Rana temporaria frogs and Cyprinus carpio carp]. / Osobennosti potentsialov deistviia predserdii i zheludochkov serdtsa liagushki Rana temporaria i karpa Cyprinus carpio

Using microelectrode technique, studies have been made on electrophysiological indices (amplitude of AP, amplitude of the plateau, latent period of AP, duration of maximal depolarization, duration of repolarization at different levels) of cells of isolated atrium and ventricles of the carp during both the spontaneous activity and electrical stimulation. The obtained amplitude-temporal parameters were compared to those of the heart in the frog R. temporaria. It was found that the amplitude of AP, the amplitude of the plateau and the duration of the latent period of AP in both the atrium and ventricles of the carp significantly (p less than 0.01) differ from the corresponding indices of the frog. On the contrary, the duration of maximal depolarization and repolarization in cells from homologous parts of the heart is very close in the species investigated.