Effects of barium on spontaneous mechanical and electrical oscillations in rat papillary muscle

In experiments on isolated rat papillary muscles the effects of Ba2+ (0.2-1 mM) on spontaneous resting tension oscillations (RTO) and membrane potential oscillations (MPO) were investigated. In normal Tyrode's solution the muscles were not spontaneously active, however, the addition of barium (1 mM) after a delay of 3-5 min induced the spontaneous excitations of the preparations. During this time period the amplitudes of RTO and MPO of the quiescent muscle increased gradually, and just before the first spontaneous beat their values were many fold above control levels. It was noted that just before the first spontaneous excitation the RTO became very synchronous and resembled the sinusoidal oscillations. By means of a special transducers the displacements of two adjacent points (distance, 1.0 mm) on a muscle surface were continuously recorded at the resting state. The correlation coefficient between these displacement signals was shown to increase from zero (before Ba2+ addition) to 0.5-0.7 (just before the first spontaneous beat). It was suggested that the enhancement of the RTO and MPO is a result of the synchronization of subthreshold electrical and mechanical activities of all muscle cells after the addition of barium.