[Study of mechanical oscillations of guinea pig atrial myocardium during cooling].

Spontaneous mechanical oscillations--period damping oscillations of isometric tension, that occur immediately after discontinuance of the preparation contraction, induced by an external stimulation were studied in the guinea-pig auricle within the temperature range 17-7 degrees C. The mechanical oscillations were established to appear at 17 degrees C. With temperature decrease the amplitude of the oscillations rose and reached maximum at 9 degrees C and then fell down. The mechanical oscillations were not attended by oscillations of the membrane potential. The amplitude and magnitude of mechanical oscillations increased with Ca2+ concentration elevation in the medium and dropped down with its diminution. Addition of caffeine (10 mM) or KCI (20 mM) to the Tirode solution resulted in complete suppression of mechanical oscillations in the presence of the drastically decreased rhythmic contractions. It is assumed that the appearance of mechanical oscillations may be caused by the increased content of Ca2+ ions in the myoplasma of myocytes. This increase is consequent on the slowing down of the sequestering ability of sarcoplasmatic reticulum (SR) on cooling. It is suggested that SR may be a greater of mechanical oscillations.