Chapter

The effects of internal Ca<sup>2+</sup> and Mg<sup>2+</sup> on ion channels in the squid giant axon

Shunichi Yamagishi, Kishio Furuya and Fumio Kukita

in Cephalopod Neurobiology

Published in print April 1995 | ISBN: 9780198547907
Published online March 2012 | e-ISBN: 9780191724299 | DOI: https://dx.doi.org/10.1093/acprof:oso/9780198547907.003.0100
The effects of internal Ca2+ and Mg2+ on ion channels in the squid giant axon

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This chapter deals with the regulatory effects of internally added Ca2+ and Mg2+ on the Na+ and K+ channel activities of an excitable membrane. The regulatory effects of internally applied Ca2+ and Mg2+ ions, using intracellularly perfused squid axons, is discussed. It has previously beeen shown using squid giant axons that the action of internal Ca2+ on Na+ channel activity causes deterioration, or little effect. The internally added Ca2+ produces a Na+ action potential without any electrical stimulation in squid axons. Low concentrations of Ca2+ and Mg2+ exist in the cytoplasm of animal cells. Changes in concentration of Ca2+ are closely related to several functions, including membrane processes such as excitability and synaptic transmission. The internally applied Ca2+ and Mg2+ commonly have two types of effect on ion channel activities. First, they cause a lowering of the threshold voltage level for Na+ and K+ channel activation. The lowering of threshold potential caused by Ca2+ and Mg2+ is a notable and important effect which suggests that the membrane becomes more excitable in the presence of increased levels of intracellular divalent cations. Second, the internally applied Ca2+ and Mg2+ reduce Na+ and K+ currents by a concentration-dependent amount that differs for internally applied Ca2+ and Mg2+ respectively. The similarities and differences between Ca2+ and Mg2+ effects on ion channel activities are also described.

Keywords: ion channels; cytoplasm; internal Ca2+; internal Mg2+; Na+ channel; K+ channel; synaptic transmission

Chapter.  2682 words.  Illustrated.

Subjects: Neuroscience

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