Mg2+ and Excitable Membranes

The present book is the outcome of a symposium on magnesium and excitable membranes, held in September 1989 on the occasion of the 12th annual meeting of the European Neuroscience Associ ation in Torino. Leading specialists from around the world met in order to discuss the physiological and clinical effects of magne sium on excitable cells. Magnesium ions are known to playa key role in the regulation of a variety of cell functions and, as such, have been implicated in the control of neuronal excitability and cardiovascular diseases. In the last decade, the advent of new electro physiological techniques has provided important details on the modulatory action of mag nesium on ion channels and the receptor proteins of neurotrans mitters. Thus, in neuronal and muscle cells, extracellular and in is shown to block ion passage through open tracellular magnesium channels in a voltage- and time-dependent manner. The mecha nism appears to be common for voltage- and receptor-operated channels, and it is thought to be an important cofactor in the long-term potentiation of synaptic transmission, brain aging, and cardiac activity. Recent findings show that the action of internal magnesium has additional features. High and low affinity sites for internal magnesium are involved in the regulation of channel gat ings and ion permeation. Biochemical studies suggest that internal magnesium interferes with G-protein subunits, GTP-ase activity, and second messengers involved in channel phosphorylation.

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This volume presents the most recent research findings on the key role played by Mg2+ in the regulation of ion channels in excitable tissue. Contributions describe the multiple actions exerted by Mg2+ on the different types on ion channels controlling nerve and cardiac cell activity. Recent developments in the detection of single ion channel activity provide important insights into the mechanisms of action of Mg2+ at the channel level.

Contenu
Use of Ion Selective Microelectrodes to Measure Intracellular Free Mg2+.- Voltage-Gated Ionic Channels: Diversity and Modulation by Mg2+.- ATP-Dependent K+ Channels of Excitable Membranes.- Voltage-Dependent Blockage of Cardiac Inwardly Rectifying K+ Channels by Internal Mg2+.- Regulation of the Voltage-Gated Ca2+ Current by Intracellular Free Mg2+ Studied by Internal Perfusion of Single Cardiac Myocytes.- Blockage of Neuronal Low-Threshold Ca2+ Channels by Extracellular Mg2+.- Dual Blockage by Mg2+ of the N-Methyl-D-Aspartate-Activated Channel.- Excess Mg2+ and Central Nervous System Metabolism.- Mg2+ in Neurotrauma: Its Role and Therapeutic Implications.