Magnesium ions and ionic channels: activation, inhibition or block--a hypothesis.

The interactions between magnesium ions and ionic membrane channels are complicated and may be classified in three categories: activation, reduction and inhibition of the ionic fluxes across the channels, corresponding to three mechanisms: open-block-close. The interactions between magnesium ions and various ionic channels are reviewed and the explanations of the three mechanisms are analyzed in term of screening/binding effects on the membrane surface polar head groups.