Title: Extracellular Mg2+ regulates activation of rat eag potassium channel.

Authors: H Terlau, J Ludwig, R Steffan, O Pongs, W Stühmer, S H Heinemann

Journal, date & volume: Pflugers Arch., 1996 Jun , 432, 301-12

PubMed link: http://www.ncbi.nlm.nih.gov/pubmed/8662307

Abstract
The rat homologue of Drosophila ether à gogo cDNA (rat eag) encodes voltage-activated potassium (K) channels with distinct activation properties. Using the Xenopus expression system, we examined the importance of extracellular Mg2+ on the activation of rat eag. Extracellular Mg2+ at physiological concentrations dramatically slowed the activation in a dose- and voltage-dependent manner. Other divalent cations exerted similar effects on the activation kinetics that correlated with their enthalpy of hydration. Lowering the external pH also resulted in a slowing of the activation. Protons competed with Mg2+ as the effect of Mg2+ was abolished at low pH. A kinetic model for rat eag activation was derived from the data indicating that all four channel subunits undergo a Mg2+-dependent conformational transition prior to final channel activation. The strong dependence of rat eag activation on both the resting potential and the extracellular Mg2+ concentration constitutes a system for fine-tuning K channel availability in neuronal cells.