Das Aktionspotential des isolierten Ranvierschen Schnürrings bei Erhöhung der extracellulären Wasserstoffionen-Konzentration in calciumhaltigen und calciumarmen Lösungen

Summary

1. Effects of raising extracellular hydrogen-ion-concentration [H⁺] _e on the action potential (AP) of isolated nodes of Ranvier in calcium-containing (1.08 mMol/l) and in calciumpoor (0.05 mMol/l) solutions were studied between ph 7 and 4.8.

2. Threshold membrane potential (i.e. maximum subthreshold response) and membrane potential at the end of the slow first falling phase increase with increasing [H⁺] _e , especially below ph 6.5. The amplitude of the AP is slightly raised.

3. Mild lowering of ph from 7 to 6.5 in Ca-containing solutions accelerates repolarization, mainly during the slow first phase. In Ca-poor solution, small drop in ph reverses the effects of Ca-lack.

4. Below ph 6.5 to 6.0, repolarization is delayed, mainly during the slow first phase and, to a smaller extent, during the negative after-potential. At low ph the AP becomes insensitive to lack of extracellular calcium.

5. Between ph 7 and 6.5 H⁺-ions are suggested mainly to act in an indirect way by raising Ca-activity in or at the membrane, thus accelerating the decrease of P _Na or the increase in P _K. From the effects at lower ph-values it is concluded that in this range H⁺-ions act directly on the membrane; they would delay and decrease the change of P _K during the AP.