Ca−K Bi-ionic action potential in squid giant axons |
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Authors: | Susumu Terakawa |
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Institution: | (1) Laboratory of Neurobiology, National Institute of Mental Health, 20205 Bethesda, Maryland;(2) Marine Biological Laboratory, 02543 Woods Hole, Massachusetts;(3) Present address: Department of Cellular Physiology, National Institute for Physiological Sciences, 444 Okazaki, Japan |
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Abstract: | Summary Under intracellular perfusion with a solution containing K+ as the sole cation species, squid giant axons were found to be capable of developing all-or-none action potentials when immersed in a medium in which CaCl2 was the only electrolyte. The adequate range of ion concentration for demonstrating this capability was mentioned. The reversal potential level measured by the voltage-clamp technique varied directly with the logarithm of the concentration of extracellular Ca-ion; the proportionality constant was close toRT/2F. The action potential observed under this Ca–K bi-ionic condition could not be suppressed by addition of tetrodotoxin or saxitoxin to the external medium. The external Ca-ion could be replaced with Co- or Mn-ion without eliminating the capability of the axons to develop action potentials. D-600 could not suppress the inward current observed under the voltage-clamp condition, but 4-aminopyridine could suppress it. The experimental findings were interpreted based on the current channel hypothesis and on the macromolecular theory. |
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Keywords: | bi-ionic action potential Ca-dependent action potential K-channel squid axon 4-aminopyridine |
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