THE actin cytoskeleton is an important contributor to the integrity of cellular shape and responses in neurons. However, the molecular mechanisms associated with functional interactions between the actin cytoskeleton and neuronal ion channels are largely unknown. Wholecell and single channel recording techniques were thus applied to identified retinal bipolar neurons of the tiger salamander (Ambystoma tigrinu)mto assess the role of acute changes in actin-based cytoskeleton dynamics in the regulation of voltage-gated ion channels. Disruption of endogenous actin filaments after brief treatment (20–30 min) with cytochalasin D (CD) activated voltagegated K+currents in bipolar cells, which were largely prevented by intracellular perfusion with the actin filament-stabilizer agent, phalloidin. Either CD treatment under cell-attached conditions or direct addition of actin to excised, inside-out patches of bipolar cells activated and/or increased single K+channels. Thus, acute changes in actin-based cytoskeleton dynamics regulate voltagegated ion channel activity in bipolar cells.