The effect of different ionic levels on the electrical response of toad skin to noradrenaline

1. After the addition of noradrenaline (final concentration 4 x 10(-5)M) to the inner medium of isolated toad skins, they underwent a depolarization (inner surface becoming less positive) followed by a hyperpolarization.2. The dependence of the minimal and maximal levels of the depolarizing and hyperpolarizing phases of the response upon the external concentrations of sodium and chloride ions was examined.3. The experimental data were considered to support the view that the hyperpolarization was generated by an increase in the sodium to chloride permeability ratio for the outer barrier of the skin and that the depolarization resulted from a transient increase in the conductance of transient shunt pathways in the skin.4. When the external sodium and chloride ions were replaced by magnesium (or potassium) and sulphate ions, noradrenaline initiated a transient hyperpolarization. During this hyperpolarizing response the time course of the change in the skin's conductance resembled that of the skin potential. The polarity of the response was changed by reversing the chloride concentration gradient across the skin.5. The dependence of the maximal level of the hyperpolarizing response upon the internal potassium concentration was examined.6. It was concluded that the hyperpolarizing response was generated partially by an increase in the potassium to chloride permeability ratio for the inner barrier of the skin and predominantly by the movement of chloride and accompanying cations through a transient shunt pathway, probably the active glands.