Ca-K bi-ionic action potential in squid giant axons.
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 to RT/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.
D015761:4-Aminopyridine; D000200:Action Potentials / Q000187:drug effects; D000631:Aminopyridines / Q000494:pharmacology; D000818:Animals; D001369:Axons / Q000502:physiology*; D002118:Calcium / Q000494:pharmacology*; D003035:Cobalt / Q000494:pharmacology; D049832:Decapodiformes; D005711:Gallopamil / Q000494:pharmacology; D008345:Manganese / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D009467:Neuromuscular Depolarizing Agents / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology*; D013779:Tetrodotoxin / Q000494:pharmacology
D000631:Aminopyridines; D009467:Neuromuscular Depolarizing Agents; D005711:Gallopamil; D003035:Cobalt; D008345:Manganese; D013779:Tetrodotoxin; D015761:4-Aminopyridine; D011188:Potassium; D002118:Calcium