ANNEXINS FROM EHRLICH ASCITES-CELLS INHIBIT THE CALCIUM-ACTIVATED CHLORIDE CURRENT IN XENOPUS-LAEVIS OOCYTES

The effect of annexins II, III and V, purified from different species, on the calcium-activated chloride current across the stage-V to stage -VI Xenopus laevis oocyte membrane was tested either directly, using c alcium entry mediated by depolarization, by A23187 permeabilization of oocytes or indirectly by quisqualate stimulation of a metabotropic gl utamate receptor in the membrane expressed by the oocyte after injecti on of mRNA. The annexins isolated from the Ehrlich ascites cell, which is a mouse tumor cell, were found to be potent inhibitors of the chlo ride current, showing half-maximal inhibition at 50 nM, whereas no blo ck was found using bovine or porcine annexins isolated from lung tissu e. Of the annexins tested, we found annexin III to be naturally occurr ing in the oocyte, while only trace amounts of annexins II and V could be demonstrated. The inhibition pattern varied somewhat according to the stimulus method, the inhibition being more complete when an indire ct stimulus via the metabotropic receptor was applied compared to a di rect calcium stimulus.