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Electrophysiology of squid Schwann cells
Abbott, N.J.; Brown, E.R.; Pichon, Y.; Kukita, F. (1995). Electrophysiology of squid Schwann cells, in: Abbott, N.J. et al. (Ed.) Cephalopod neurobiology: neuroscience studies in squid, octopus and cuttlefish. pp. 197-212
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| Auteurs | | Top |
- Abbott, N.J.
- Brown, E.R.
- Pichon, Y.
- Kukita, F.
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| Abstract |
Schwann cells of the squid giant nerve fibre form a monolayered sheath around the axon. The accessibility and size of the cells permits microelectrode impalement. The membrane potential is around -40 mV at rest, the result of a membrane predominantly permeable to K+. The Schwann cell has a lower internal [K+] and higher [Na+] than the giant axon, which helps explain the low membrane potential. Resting Cl permeability has not been accurately measured, but may be significant; Cl- distribution across the membrane appears to be close to equilibrium. The input impedance of squid Schwann cells is between 3 and 13MΩ. Calculations of membrane resistance depend on assumptions about the effective surface area of the membrane, but figures of 1.2-4.8 kΩ.cm² have been derived, compared with about 1 kΩ.cm² for the axon membrane. Schwann cells are weakly dye- and electrically-coupled in small groups, but the nature of the junctions responsible is unclear. Current injection provides evidence of non-ohmic membrane behaviour, and 'spike-like' transients of potential to depolarizing current steps. Axonal stimulation or addition of glutamate or carbachol causes a long-lasting hyperpolarization of the Schwann cell, associated with increased K+-selectivity of the membrane. Transient hyperpolarizations are often seen during this activation, and appear to be due to opening of calcium-activated K+ channels. The membrane properties may underlie important activities of the Schwann cell including periaxonal ion homeostasis and axon-Schwann cell signalling. The similarities in membrane properties with vertebrate Schwann cells suggest that axon-associated peripheral glial cells may function on similar general principles in vertebrates and invertebrates. |
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