Involvement of calcium and cytoskeleton in gallbladder epithelial cell volume regulation

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Abstract
The importance of Ca and cellular cytoskeletal elements in the activation or control of volume regulation by epithelial cells was explored in Necturus gallbladder. Gallbladder cells were previously shown to rapidly readjust their volumes to control size after osmotic perturbation of the mucosal bathing solution. Removal of Ca from the perfusates caused dramatic morphological changes that prevented assessment of the role of extracellular Ca in volume regulation. The regulatory volume increase (RVI) that follows shrinkage of the cell due to perfusion of a hypertonic mannitol solution is insensitive to agents that interfere with cell Ca- or calmodulin-mediated events (quinidine, trifluoperazine) and is not blocked by agents that cause changes in the cytoskeleton (colchicine, cytochalasin B). Osmotically induced cell swelling is followed by regulatory volume decrease (RVD), which is inhibited by agents that interfere with Ca-dependent processes (quinidine, trifluoperazine) and by the microfilament inhibitor, cytochalasin B. RVD apparently depends on Ca, calmodulin and an intact microfilament network, whereas RVI is independent of these factors.