Purification of a soluble protein controlling ca channel activity in paramecium

Recent advances in the molecular genetics of Paramecium

Paramecium continues to be used to study motility, behavior, exocytosis, and the relationship between the germ and the somatic nuclei. Recent progress in molecular genetics is described. Toward cloning genes that correspond to mutant phenotypes, a method combining complementation with microinjected DNA and library sorting has been used successfully in cloning several novel genes crucial in membrane excitation and in trichocyst discharge. Paramecium transformation en masse has now been shown by using electroporation or bioballistics. Gene silencing has also been discovered in Paramecium, recently. Some 200 Paramecium genes, full length or partial, have already been cloned largely by homology. Generalizing the use of gene silencing and related reverse-genetic techniques would allow us to correlate these genes with their function in vivo.

Paramecium calcium channels are blocked by a family of calmodulin antagonists

Although the voltage-sensitive Ca channel present in Paramecium has been subjected to detailed physiological and genetic analysis, no organic ligands have been described that block this channel with high affinity and that ultimately can be used to identify channel components. Based on a previous observation that the naphthalene sulfonamide calmodulin antagonist W-7 can block Paramecium Ca channels at high concentration, we have synthesized analogs of W-7 that block these channels at concentrations of less than 1 microM. The effectiveness of these compounds was tested both by a sensitive behavioral assay and on Ca channels that had been incorporated into planar lipid bilayers. Despite the fact that these compounds are effective Paramecium calmodulin antagonists, two independent lines of evidence suggest that W-7 and its analogs block the Ca channel by a mechanism that is independent of their action on calmodulin. In addition, the sensitivity to W-7 or dihydropyridines of Ca channels present in a number of eukaryotic phyla has been used to identify similarities in Ca channels from widely diverse organisms. It appears that the pharmacological specificity provides a means to group Ca channels.

Exocytosis induction in Paramecium tetraurelia cells by exogenous phosphoprotein phosphatase in vivo and in vitro: possible involvement of calcineurin in exocytotic membrane fusion

Since it had been previously shown that in Paramecium cells exocytosis involves the dephosphorylation of a 65-kD phosphoprotein (PP), we tried to induce exocytotic membrane fusion by exogenous phosphatases (alkaline phosphatase or calcineurin [CaN]). The occurrence of calmodulin (CaM) at preformed exocytosis sites (Momayezi, M., H. Kersken, U. Gras, J. Vilmart-Seuwen, and H. Plattner, 1986, J. Histochem. Cytochem., 34:1621-1638) and the current finding of the presence of the 65-kD PP and of a CaN-like protein in cell surface fragments ("cortices") isolated from Paramecium cells led us to also test the effect of antibodies (Ab) against CaM or CaN on exocytosis performance. Microinjected anti-CaN Ab strongly inhibit exocytosis. (Negative results with microinjected anti-CaM Ab can easily be explained by the abundance of CaM.) Alternatively, microinjection of a Ca2+-CaM-CaN complex triggers exocytosis. The same occurs with alkaline phosphatase. All these effects can also be mimicked in vitro with isolated cortices. In vitro exocytosis triggered by adding Ca2+-CaM-CaN or alkaline phosphatase is paralleled by dephosphorylation of the 65-kD PP. Exocytosis can also be inhibited in cortices by anti-CaM Ab or anti-CaN Ab. In wild-type cells, compounds that inhibit phosphatase activity, but none that inhibit kinases or proteases, are able to inhibit exocytosis. Exocytosis cannot be induced by phosphatase injection in a membrane-fusion-deficient mutant strain (nd9-28 degrees C) characterized by a defective organization of exocytosis sites (Beisson, J., M. Lefort-Tran, M. Pouphile, M. Rossignol, and B. Satir, 1976, J. Cell Biol., 69:126-143). We conclude that exocytotic membrane fusion requires an adequate assembly of molecular components to allow for the dephosphorylation of a 65-kD PP and that this step is crucial for the induction of exocytotic membrane fusion in Paramecium cells. In vivo this probably involves a Ca2+-CaM-stimulated CaN-like PP phosphatase.

Voltage-dependent calcium channels from Paramecium cilia incorporated into planar lipid bilayers

Two different divalent cation-selective channels from Paramecium cilia were incorporated into planar lipid bilayers. Both channels were much more permeable to divalent than univalent cations, and one of them discriminated significantly among the divalent cations. The selectivity and voltage dependence of the latter channel are comparable to those of voltage-dependent calcium channels found in a variety of cells. A combined biochemical, biophysical, and genetic study of calcium channels is now possible.