Re: How do contractile vacuole's in a paramecium expel water?

To tell you the truth, we aren't sure how exactly contractile vacuoles work but there are a few studies that have shown some possible mechanisms. In pioneering studies, Kitching (1952 Symp. Soc. exp. Bio. 6:145-165) pointed out that surface tension at the vauole membrane produced pressure required to discharge fluid. One study suggests that the vacuoles work on a actin-myosin basis, similar to muscle contraction...Doberstein et. al. (1993 Nature 365, 841-843). Breifly, they introduced an antibody against the myosin-IC phosphorylation site into a living Acanthamoeba sp., which interfered with it's contractile vacuole activity. In a recent study by Naitoh et. al.(1997 J. Exp. Bio. 200:713- 721) suggests that the internal pressure of the vacuole is caused by cytosolic pressure and that the fluid-seggregation mechanism does not affect the fluid discharge mechanism. You can email Dr. Naitoh for further explanation at naitoh@pbrc.hawaii.edu.