[Spontaneous contractions and the visco-elastic properties of the isolated guinea-pig gall-bladder]

The isolated guinea-pig gall-bladder showed the spontaneous changes in luminal pressure at the rate of 7-12/min at 38 degrees C. These spontaneous contractions were increased in rates as the increase in luminal volume. On the other hand, they were reduced in rates and in amplitudes by lowering the temperatures. Decrease in [Ca2+]o from 2.4 mM to 0.8 mM depressed or even abolished the spontaneous contractions, whereas increase in [Ca2+]o from 2.4 mM to 7.2 mM produced slow pressure rise accompanied with small pressure fluctuations, suggesting that [Ca2+]i was increased as the results of facilitation of Na-Ca exchange mechanism. The pressure-volume relation measured during the first inflation was steeper than that during the following deflation; namely, the gall-bladder showed plasticity. The visco-elastic property was investigated by recording the time course of the pressure change, stress relaxation, following the sudden increase in volume. Thus, the tissue visco-elasticity was divided into three components; the instantaneous elastic component and two viscoelastic components that had the time constants of 4-12 sec and of 5-10 min.