Mechanisms of Mg2+ influx, efflux and intracellular 'muffling' in leech neurones and glial cells

Mg2+ is known to influence conductance and gating properties of a multitude of ion channels and is thus able to modulate synaptic transmission. Theref ore, a tight regulation of the intracellular. free Mg2+ concentration ([Mg2 +](i)) in neurones and glial cells is crucial for maintaining the functions of central nervous systems. [Mg2+](i) is regulated through the balance of Mg2+ influx and Mg2+ efflux, together with heavy damping of [Mg2+](i) chang es through intracellular buffering and sequestration. To investigate the me chanisms involved in [Mg2+](i) regulation, neurones and glial cells from th e central nervous system of the leech Hirudo medicinalis proved to be an id eal model system. The present article summarizes the evidence for a Mg2+ in flux pathway which is distinct from that for Ca2+, for a dual regulation of Mg2+ efflux (a 1 Na+/l Mg2+ antiport and a Na+-independent Mg2+ efflux mec hanism), for pH-dependent Mg2+ buffering through ATP and other intracellula r Mg2+ binding components and for the involvement of mitochondria in intrac ellular Mg2+ sequestration.