Weitere Untersuchungen �ber den passiven Ionentransport durch die erregbare Membran des Ranvierknotens

Effect of external ammonium on the kinetics of the sodium current in frog muscle

The effect of externally applied 20 mM NH4Cl on steady-state Na+ inactivation h infinity and other electrical parameters has been studied in voltage-clamped frog muscle fibres. Exposure to Ringer with 20 mM NH4Cl causes a small transient shift of the h infinity (E) curve to more positive potentials. Upon return to normal slowly into the original position. Similar but smaller shifts of the descending branch of the INa (E) curve, of the PNa(E) curve and of the time to peak curve are also observed. The shifts are thought to result from the changes in intracellular pH which occur during and after NH4Cl application. The observations are compatible with the idea that intracellular pH affects the surface charge potential at the inner side of the membrane.

Permeability of the endplate membrane activated by acetylcholine to some organic cations

The ability of various organic cations to depolarize the ACh-activated endplate membrane in the absence of Na ions was examined on frog sartorius muscle by measuring the endplate potential on the muscle surface with the moving electrode technique. The ACh-activated endplate membrane was very permeable to ammonium and its methyl and hydroxy derivatives, and moderately permeable to guanidine derivatives and Tris (hydroxymethyl) aminomethane. The permeability of alkylol derivatives of ammonium diminished progressively with increase in molecular size. The present results suggested that the endplate ionic channels can be represented by a pore of about 6.4 A in diameter.

Ammonium and chloride extrusion: hyperpolarizing synaptic inhibition in spinal motoneurons

The reversal potential of postsynaptic inhibition shifts toward resting membrane potentials in cat spinal motoneurons after intravenous infusion of ammonium salts(1 to 3 millimoles per kilogram of body weight). Simultaneously, the depolarizing action of intracellularly injected chloride ions on the inhibitory membrane is enhanced and recovery therefrom is prolonged. Passive membrane properties remain unaltered. The results indicate a blocking of active extrusion of chloride which normally maintains a high ionic gradient for hyperpolarizing inhibition.