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Cephalopod NeurobiologyNeuroscience Studies in Squid, Octopus and Cuttlefish$
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N. Joan Abbott, Roddy Williamson, and Linda Maddock

Print publication date: 1995

Print ISBN-13: 9780198547907

Published to Oxford Scholarship Online: March 2012

DOI: 10.1093/acprof:oso/9780198547907.001.0001

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The effects of internal Ca2+ and Mg2+ on ion channels in the squid giant axon

The effects of internal Ca2+ and Mg2+ on ion channels in the squid giant axon

Chapter:
(p.153) 11 The effects of internal Ca2+ and Mg2+ on ion channels in the squid giant axon
Source:
Cephalopod Neurobiology
Author(s):

Shunichi Yamagishi

Kishio Furuya

Fumio Kukita

Publisher:
Oxford University Press
DOI:10.1093/acprof:oso/9780198547907.003.0100

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

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