Abstract
We have studied the admittance of the membrane of squid giant axon under voltage clamp in the absence of ionic conductances in the range of 0-12 kHz for membrane potentials (V) between --130 and 70 mV. The admittance was measured at various holding potentials (HP) or 155 ms after pulsing from a given holding potential. Standard P/4 procedure was used to study gating currents in the same axons. We found that the membrane capacity Cm (omega) is voltage as well as frequency dependent. For any given V, the voltage-dependent part of the membrane capacitance has a maximum as the frequency approaches zero and requires at least a two-time constant equivalent circuit to be described. When the holding potential is varied, the voltage-dependent capacitance follows a bell- shaped curve with a maximum change of 0.15 muF/cm2 at about --60 mV. With the pulse method, the maximum is at --40 mV for HP = --70 and it shifts to --70 mV for HP = 0. The shift in the maximum of the voltage- dependent capacitance is consistent with the shift in the charge (Q) vs. V curve observed in our experiments with regular P/4 procedure when the HP is varied. Our data can be explained qualitatively by a four- state model for the sodium channel gating, where a charged particle can move within the field and interact with another particle not affected by the field.
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Selected References
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- Armstrong C. M., Bezanilla F. Charge movement associated with the opening and closing of the activation gates of the Na channels. J Gen Physiol. 1974 May;63(5):533–552. doi: 10.1085/jgp.63.5.533. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Armstrong C. M., Bezanilla F. Currents related to movement of the gating particles of the sodium channels. Nature. 1973 Apr 13;242(5398):459–461. doi: 10.1038/242459a0. [DOI] [PubMed] [Google Scholar]
- Armstrong C. M., Bezanilla F. Inactivation of the sodium channel. II. Gating current experiments. J Gen Physiol. 1977 Nov;70(5):567–590. doi: 10.1085/jgp.70.5.567. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Armstrong C. M., Gilly W. F. Fast and slow steps in the activation of sodium channels. J Gen Physiol. 1979 Dec;74(6):691–711. doi: 10.1085/jgp.74.6.691. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Bezanilla F., Taylor R. E., Fernández J. M. Distribution and kinetics of membrane dielectric polarization. 1. Long-term inactivation of gating currents. J Gen Physiol. 1982 Jan;79(1):21–40. doi: 10.1085/jgp.79.1.21. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Clausen C., Fernandez J. M. A low-cost method for rapid transfer function measurements with direct application to biological impedance analysis. Pflugers Arch. 1981 Jun;390(3):290–295. doi: 10.1007/BF00658279. [DOI] [PubMed] [Google Scholar]
- Fishman H. M., Moore L. E., Poussart D. Asymmetry currents and admittance in squid axons. Biophys J. 1977 Aug;19(2):177–183. doi: 10.1016/S0006-3495(77)85578-1. [DOI] [PMC free article] [PubMed] [Google Scholar]
- HODGKIN A. L., HUXLEY A. F. A quantitative description of membrane current and its application to conduction and excitation in nerve. J Physiol. 1952 Aug;117(4):500–544. doi: 10.1113/jphysiol.1952.sp004764. [DOI] [PMC free article] [PubMed] [Google Scholar]
- HODGKIN A. L., HUXLEY A. F., KATZ B. Measurement of current-voltage relations in the membrane of the giant axon of Loligo. J Physiol. 1952 Apr;116(4):424–448. doi: 10.1113/jphysiol.1952.sp004716. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Keynes R. D., Rojas E. The temporal and steady-state relationships between activation of the sodium conductance and movement of the gating particles in the squid giant axon. J Physiol. 1976 Feb;255(1):157–189. doi: 10.1113/jphysiol.1976.sp011274. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Meves H. The effect of holding potential on the asymmetry currents in squid gaint axons. J Physiol. 1974 Dec;243(3):847–867. doi: 10.1113/jphysiol.1974.sp010780. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Takashima S. Frequency domain analysis of asymmetry current in squid axon membrane. Biophys J. 1978 Apr;22(1):115–119. doi: 10.1016/S0006-3495(78)85475-7. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Taylor R. E., Bezanilla F. Comments on the measurement of gating currents in the frequency domain. Biophys J. 1979 May;26(2):338–340. doi: 10.1016/S0006-3495(79)85255-8. [DOI] [PMC free article] [PubMed] [Google Scholar]