Figure 4. Inhibition by La³⁺ of low [K⁺]_o-induced irregular, transient depolarizations and action potentials.

A, switching from 5.4 to 0.1 mm K⁺ solution at the first arrow caused gradual hyperpolarization, irregular, transient depolarizations and an action potential with a sustained plateau. The action potential was terminated by increasing [K⁺]_o to 5.4 mm at the second arrow. Thereafter, introduction of 0.1 mm K⁺ solution together with 0.1 mm La³⁺ at the first arrow caused greater hyperpolarization, smaller transient depolarizations, and no action potential (lower sweep). B, rising phase of the action potential (shown in panel A) depicted on an expanded time scale.