A quantitative analysis of the slow component of delayed rectification in frog atrium.

1. The slow component of delayed rectification in the atrial muscle membrane of Rana ridibunda has been analysed quantitatively using a voltage-clamp technique.2. It is shown that the current is proportional to a variable which obeys first-order kinetics. At negative potentials the time constant of this process is very long (tau = 3 sec at -55 mV) but it becomes faster at positive potentials (tau = 1.85 sec at +25 mV).3. In the steady state the degree of activation is a sigmoid function of potential. The activation threshold varies substantially between preparations but is usually negative to -30 mV.4. The instantaneous current-voltage relation is nearly linear and its reversal potential most frequently lies between zero and -30 mV.5. The properties of this current system resemble those of the current system i(x2) found in mammalian Purkinje fibres.