Der Einfluß von schwerem Wasser auf das stationäre Strom-Spannungsverhalten des Ranvierschen Schnürrings

A substitution of H₂O by D₂O in the extracellular Ringer's solution leads to the following changes in the current-voltage-relation of the Ranvier node: 1. The positive resistances are increased by a factor of 1.2. 2. The transition-region of the limiting values of resistance is shifted 20 mV towards depolarizing potentials. From 1. and 2. there results an increase of the negative differential resistance which is observed if the membrane potential exceeds+20 mV. These changes are observed independently of whether the current is carried by K^• (or Rb^•), or (during Veratridin-depolarization) also by Na^•, Li^• or NH₄ ^•. This effect of D₂O is comparable to the influence of increased extracellular concentration of H^• and Ca^•• as well as to increased osmolarity. All lead to increased threshold voltage of action potential according to the shift of transition-region to more positive potentials. It is shown that an explanation of the dominant influence of D₂O based merely on the differences in physico-chemical properties between H₂O- and D₂O-Ringer's solution is very unlikely. Therefore the results are understood as consequences of an influence of solvent on the excitable membrane itself. This interpretation is supported by the observation that the microscopical picture of nerve fibres, circulated with D₂O-solutions, changes in a definite manner.