PROTEIN-KINASE-C ACTIVATION DECREASES ACTIVITY-DEPENDENT ATTENUATION OF DENDRITIC NA+ CURRENT IN HIPPOCAMPAL CA1 PYRAMIDAL NEURONS

Protein kinase C activation decreases activity-dependent attenuation o f dendritic Na+ current in hippocampal CAl pyramidal neurons. J. Neuro physiol. 79: 491-495, 1998. Action potentials recorded from the soma o f CAl pyramidal neurons remain relatively uniform in amplitude during repetitive firing. In contrast, the amplitudes of back-propagating act ion potentials in dendrites decrease progressively during a spike trai n. This activity-dependent decrease in amplitude is dependent on the f requency of firing during the train and distance from the soma. Previo usly, we described a property of Na+ channels that provides a plausibl e mechanism for the activity dependence of the amplitude of the dendri tic action potentials: available Na+ current decreases during trains o f action potentials through an inactivation, distinct from fast inacti vation, that appears rapid in onset, but slow and voltage-dependent in its recovery. In this study we found that activation of protein kinas e C by phorbol esters decreased this activity-dependent inactivation o f pharmacologically isolated Na+ current in cell-attached dendritic, b ut not somatic, patches. Similarly in whole cell recordings phorbol es ters decreased the attenuation of back-propagating dendritic action po tentials during trains. These results indicate a novel effect of prote in kinase C on the dendritic Na+ channel and further support the hypot hesis that the activity dependence of the dendritic action potentials is derived from the inactivation properties of Na+ channels.