Ca2+ Nanodomain-Mediated Component of Swelling-Induced Volume-Sensitive Outwardly Rectifying Anion Current Triggered by Autocrine Action of ATP in Mouse Astrocytes

摘要

The volume-sensitive outwardly rectifying (VSOR) anion channel provides a major pathway for anion transport during cell volume regulation. It is typically activated in response to cell swelling, but how the channel senses the swelling remains unclear. Meanwhile, we recently found that in mouse astrocytes the channel is activated by an inflammatory chemical mediator, bradykinin, without cell swelling and that the activation is regulated via high concentration regions of intracellular Casup2+/sup ([Casup2+/sup]subi/sub) in the immediate vicinity of open Casup2+/sup-permeable channels, so-called Casup2+/sup nanodomains. Here we investigated whether a similar mechanism is involved in the swelling-induced VSOR channel activation in the astrocytes. A hypotonic stimulus (25% reduction in osmolality) caused the [Casup2+/sup]subi/sub rises in the astrocytes, and the rises were abolished in the presence of an ATP-degrading enzyme, apyrase (10 U/ml). Application of ATP (100 µM) under isotonic conditions generated the current through VSOR channels via Casup2+/sup nanodomains, as bradykinin does. The current induced by the hypotonic stimulus was suppressed by ～40% in the Casup2+/sup-depleted condition where the ATP-induced VSOR current was totally prevented. Thus the swelling-induced VSOR channel activation in mouse astrocytes is partly regulated via Casup2+/sup nanodomains, whose generation is triggered by an autocrine action of ATP.