Protein kinase C activation decreases activity-dependent attenuation of dendritic Na+ current in hippocampal CA1 pyramidal neurons.
Action potentials recorded from the soma of CA1 pyramidal neurons remain relatively uniform in amplitude during repetitive firing. In contrast, the amplitudes of back-propagating action potentials in dendrites decrease progressively during a spike train. This activity-dependent decrease in amplitude is dependent on the frequency of firing during the train and distance from the soma. Previously, we described a property of Na+ channels that provides a plausible mechanism for the activity dependence of the amplitude of the dendritic action potentials: available Na+ current decreases during trains of action potentials through an inactivation, distinct from fast inactivation, that appears rapid in onset, but slow and voltage-dependent in its recovery. In this study we found that activation of protein kinase C by phorbol esters decreased this activity-dependent inactivation of pharmacologically isolated Na+ current in cell-attached dendritic, but not somatic, patches. Similarly in whole cell recordings phorbol esters decreased the attenuation of back-propagating dendritic action potentials during trains. These results indicate a novel effect of protein kinase C on the dendritic Na+ channel and further support the hypothesis that the activity dependence of the dendritic action potentials is derived from the inactivation properties of Na+ channels.
Colbert
C M
CM
Division of Neuroscience, Baylor College of Medicine, Houston, Texas 77030, USA.
Johnston
D
D
D000200:Action Potentials / Q000187:drug effects*; D000818:Animals; D003712:Dendrites / Q000187:drug effects / Q000502:physiology*; D004558:Electric Stimulation; D004789:Enzyme Activation; D006624:Hippocampus / Q000502:physiology*; D066298:In Vitro Techniques; D008297:Male; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology; D010703:Phorbol Esters / Q000494:pharmacology*; D010704:Phorbols / Q000494:pharmacology; D011493:Protein Kinase C / Q000378:metabolism*; D017966:Pyramidal Cells / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D015222:Sodium Channels / Q000502:physiology*
D010703:Phorbol Esters; D010704:Phorbols; D015222:Sodium Channels; C008874:phorbol-12,13-diacetate; D015240:Phorbol 12,13-Dibutyrate; D011493:Protein Kinase C; C033085:phorbol