Actin cytoskeleton regulates ion channel activity in retinal neurons

GREG MAGUIRE, VICTORIA CONNAUGHTON, ADRIANA G. PRAT, G. ROBERT JACKSON JR AND HORACIO F. CANTIELLO

NEUROREPORT

Año: 1998 p. 665 - 670

0959-4965

Actin, the main component of the intracellular cytoskeleton, has been found in all eukaryotic cells. In neurons, the actin cytoskeleton is involved in such relevant functions as neurite growth and synapse formation . It is likely, therefore, that the actin-based cytoskeleton may play an important regulatory role in neuronal plasma membrane function, including ion channel activity. Previous studies, for example, have implicated changes in the cytoskeletal structures with neuronal cation channel function, including NMDA channel activity.2–4 Little is known, however, about the molecular steps linking ion channel activity and the neuronal actin cytoskeleton. Recent studies have determined that changes in the actin cytoskeleton dynamics target, and modify the activity of ion channel molecules, including Na+ channels in renal epithelial cells,5,6 Cl– channels in renal cortical collecting duct cells,7 the CFTR anion channel8,9 and cell volume-activated10 and renal11 K+ channels. In this study patch-clamping techniques were applied to retinal neurons of the Ambystoma tigrinum to determine whether changes in actin cytoskeleton dynamics regulate neuronal ion channel activity. Our data indicate that disruption of the neuronal actin cytoskeleton with cytochalasin D (CD) enhances whole-cell K+ currents in bipolar neurons. This effect is prevented by dialysis with the actin filament stabilizer phalloidin. At the single channel level, C also activated and/or increased single K+ channel currents in cell-attached patches. Moreover, addition of monomeric actin mimicked the CD effect in excised, inside out patches from isolated neurons. Thus, changes in actin filament organization may be considered a novel intracellular signalling mechanism for neuronal ion channel regulation that further complements the structural interactions between the actin cytoskeleton and neuronal ion channels. It is likely, therefore, that the actin-based cytoskeleton may play an important regulatory role in neuronal plasma membrane function, including ion channel activity. Previous studies, for example, have implicated changes in the cytoskeletal structures with neuronal cation channel function, including NMDA channel activity.2–4 Little is known, however, about the molecular steps linking ion channel activity and the neuronal actin cytoskeleton. Recent studies have determined that changes in the actin cytoskeleton dynamics target, and modify the activity of ion channel molecules, including Na+ channels in renal epithelial cells,5,6 Cl– channels in renal cortical collecting duct cells,7 the CFTR anion channel8,9 and cell volume-activated10 and renal11 K+ channels. In this study patch-clamping techniques were applied to retinal neurons of the Ambystoma tigrinum to determine whether changes in actin cytoskeleton dynamics regulate neuronal ion channel activity. Our data indicate that disruption of the neuronal actin cytoskeleton with cytochalasin D (CD) enhances whole-cell K+ currents in bipolar neurons. This effect is prevented by dialysis with the actin filament stabilizer phalloidin. At the single channel level, C also activated and/or increased single K+ channel currents in cell-attached patches. Moreover, addition of monomeric actin mimicked the CD effect in excised, inside out patches from isolated neurons. Thus, changes in actin filament organization may be considered a novel intracellular signalling mechanism for neuronal ion channel regulation that further complements the structural interactions between the actin cytoskeleton and neuronal ion channels.