ADH-induced depolymerization of F-actin in the toad bladder granular cell: a confocal microscope study

Antidiuretic hormone (ADH) induces the fusion of cytoplasmic vesicles containing water channels with the apical membrane of the toad bladder granular cell. Fusion is accompanied by a 30% depolymerization of F-actin. We have used confocal microscopy to determine the region in the cell that undergoes depolymerization. Bladders were mounted in a split chamber, and control halves and halves stimulated by ADH for 15 min were fixed and then stained with rhodamine phalloidin. Vertical sections through the cells were obtained by confocal microscopy, and the fluorescence intensity of the apical and side regions of the cells was determined. To normalize the data, the apex-side intensity was determined for each cell, and these ratios measured for control and ADH-treated halves. In six paired experiments, the ratio for control halves was 3.69 +/- 0.50 and for ADH-treated halves was 2.61 +/- 0.33; the decrease was significant and in good agreement with earlier studies. Thus actin depolymerization takes place in a hormone-sensitive apical pool where vesicle fusion occurs and supports the view that actin depolymerization may be required for fusion.