Abstract
The maxi-anion channel is widely expressed in animal cells. We have recently demonstrated that this channel fulfils a general physiological function as an ATP-conductive gate for cell-to-cell purinergic signaling. However, the regulatory mechanisms of the maxi-anion channel remain poorly understood. We studied the activation mechanism of the maxi-anion channel in inside-out patches excised from mammary C127 cells. The channels activated upon excision in Ca-free solution in the presence of 1 mM Mg2+ and absence of ATP. Increasing both Ca2+ and Mg2+ ion concentration led to a dramatic increase in the rate of channel activation. Half-maximal activation occurred at the concentration of 0.0012 mM for Ca2+ ions and 2.8 mM for Mg2+ ions. MgATP added to bath (intracellular) solution greatly suppressed the channel activation with half-maximal inhibition at 0.037 mM. A non-hydrolysable analogue of ATP, AMP-PNP, did not suppress the channel activation suggesting that ATP hydrolysis (presumably, the channel phosphorylation) is necessary for the channel inactivation. When all Mg2+ ions were washed out, the free ATP still suppressed the channel, indicating that binding of free ATP can also close the pre-activated maxi-anion channel. Thus, the regulatory control mechanism of the maxi-anion channel involves divalent cation-dependent steps and possibly phosphorylation. [J Physiol Sci. 2006;56 Suppl:S115]
