The effects of internal Ca²+ and Mg²+ on ion channels in the squid giant axon
Yamagishi, S.; Furuya, K.; Kukita, F. (1995). The effects of internal Ca²+ and Mg²+ on ion channels in the squid giant axon, in: Abbott, N.J. et al. (Ed.) Cephalopod neurobiology: neuroscience studies in squid, octopus and cuttlefish. pp. 153-160
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| Auteurs | | Top |
- Yamagishi, S.
- Furuya, K.
- Kukita, F.
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| Abstract |
During intracellular perfusion with a 25 mM K+ solution containing Ca²+ in the range 0.1 to 10 mM, the action potential of the squid giant axon gradually decreased in amplitude, while the duration was transiently prolonged. The threshold potential for the initiation of the action potential was markedly lowered towards the resting potential level. A standard voltage clamp method was applied for the measurement of Na+ (INa.) and K+ currents (IK). The amplitude of INa and IK were reduced by internal addition of 1-30 mM Ca²+ or Mg²+ to a 100 mM K+ solution. At the same time, a shift of the 1-V curve in the negative voltage direction was observed. Up to 4 mM, the values for the voltage shift of INa for an e-fold change in Ca²+ and Mg²+ concentration were 7 mV and 8 mV respectively. INa and IK were gradually reduced by the increase in internal Ca²+ or Mg²+ concentration. The time constants for INa reduction by Ca²+ and Mg²+ were 2.0 min and 1.8 min, respectively. The apparent dissociation constants (KD) of INa reduction by Ca²+ and Mg²+ were 2.3 mM and 7.0 mM, respectively. IK was reduced more quickly but less effectively than INa by Ca²+ and Mg²+ application. |
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