Annexins from Ehrlich ascites cells inhibit the calcium-activated chloride current in Xenopus laevis oocytes

Abstract

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 calcium entry mediated by depolarization, by A23187 permeabilization of oocytes or indirectly by quisqualate stimulation of a metabotropic glutamate receptor in the membrane expressed by the oocyte after injection of mRNA. The annexins isolated from the Ehrlich ascites cell, which is a mouse tumor cell, were found to be potent inhibitors of the chloride current, showing half-maximal inhibition at 50 nM, whereas no block was found using bovine or porcine annexins isolated from lung tissue. Of the annexins tested, we found annexin III to be naturally occurring 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 indirect stimulus via the metabotropic receptor was applied compared to a direct calcium stimulus.

Electrical recordings of the mitochondrial calcium uniporter in Xenopus oocytes

“…S1). The mechanism underlying this Ca 2+ -activated Cl − channel down-regulation is unclear, but similar phenomena have been reported before when foreign proteins were expressed in Xenopus oocytes (Jorgensen et al, 1997; Kunzelmann et al, 1997). With I CACC inactivated, I MCU can now be isolated without EGTA injection (Fig.…”