Groen J, Van Mastrigt R, Bosch R
Department of Urology-urodynamics, Erasmus University Rotterdam, The Netherlands.
Acta Physiol Scand. 1996 Apr;156(4):475-82. doi: 10.1046/j.1365-201X.1996.463178000.x.
Isovolumetric contractions were induced electrically in five guinea-pig bladders in a 1.8 mM Ca2+ buffer solution at two different volumes. The rate of pressure development was studied by analysis of phase-plots, which are plots of the rate of change of intravesical pressure as a function of pressure. At relatively large volumes the rate of pressure development showed a biphasic nature, suggesting that two different processes were involved in different phases of contraction. Extracellular Ca2+ was manipulated to identify these processes. Removal of extracellular Ca2+ led to an 85% reduction of the maximum isovolumetric pressure in subsequent stimulations, but pressure developed faster. The biphasic nature of pressure development at large volumes tended to disappear. It was concluded that at large bladder volumes pressure development in this type of smooth muscle is determined by the release of intracellularly stored Ca2+ in the early phase of contraction. In the final phase the rate of pressure development is limited by the extracellular Ca2+ influx. At small bladder volumes the Ca2+ influx takes place at a higher rate, so that the contribution of intracellular Ca2+ release to pressure development could not be identified at these volumes.
在1.8 mM钙离子缓冲溶液中，对五只豚鼠膀胱在两个不同体积下进行电诱导等容收缩。通过分析相图研究压力上升速率，相图是膀胱内压变化率与压力的关系图。在相对较大体积时，压力上升速率呈双相性，表明在收缩的不同阶段涉及两个不同过程。通过操控细胞外钙离子来识别这些过程。去除细胞外钙离子导致后续刺激中最大等容压力降低85%，但压力上升更快。大体积时压力上升的双相性趋于消失。得出结论，在膀胱大体积时，这种平滑肌的压力上升在收缩早期由细胞内储存钙离子的释放决定。在最后阶段，压力上升速率受细胞外钙离子内流限制。在膀胱小体积时，钙离子内流速率更高，因此在这些体积下无法确定细胞内钙离子释放对压力上升的贡献。
