Blockage of Neuronal Low-Threshold Ca2+ Channels by Extracellular Mg2+
Mg2+ belongs to the category of abundant extracellular and intracellular cations and has biologically relevant chemical properties (for review see Flatman 1984). Mg2+ ions are small compared with other earth alkaline ions and have a large hydration shell. Water substitution in Mg2+ aquocomplexes by ligands is known to occur by 3–4 orders of magnitude slower than in Ca2+ aquocomplexes (Diebler et al. 1969). Specificity of the binding of a comparably small metal ion like Mg2+ demands that the ligand be more tightly bound than the water to be substituted. Thus, Mg2+ ions are expected to pass with difficulty through small, water-filled channels of the excitable membrane. On the other hand, if Mg2+ ions are to compete effectively with other cations for passage, a ligand is required that binds the Mg2+ ion sufficiently tightly. Channels that are specifically permeable to divalent cations appear to be interesting candidates for studying these assumptions.
KeywordsMagnesium Hydration EGTA Zucker CsCl
Unable to display preview. Download preview PDF.
- Carbone E, Lux HD (1987 c) External Ca2+ ions block unitary Na+ currents through Ca2+ channels of cultured chick sensory neurones by favouring prolonged closures. J Physiol (Lond) 382:124PGoogle Scholar
- Lux HD, Carbone E (1987) External Ca ions block Na-conducting Ca channel by promoting open to closed transitions. In: Ovchinnikov YA, Hucho E (eds) Receptors and ion channels. De Gruyter, New York, pp 149–155Google Scholar