title: Diacylglycerol-induced activation of protein kinase C attenuates Na+ currents by enhancing inactivation from the closed state.
abstract: The causes of attenuation of Na+ currents by diacylglycerol (DAG)-induced protein kinase C (PKC) activation in mouse neuroblastoma N1E-115 cells were investigated using the cell-attached patch, and the perforated-patch (nystatin based) whole-cell voltage-clamp techniques. Activation of PKC by DAG attenuated Na+ currents. Attenuation occurred in the absence of significant changes in the time-course of Na+ currents. However, the steady-state inactivation curve of these currents shifted to more negative voltages by approximately 20 mV. Here we demonstrate that the time-course of inactivation is accelerated by treatment with DAG-like substances in a voltage-dependent manner (time constant of inactivation decreased by 2- and 3.6-fold at -60, and -30 mV, respectively). In cell-attached patches, treatment with DAG compounds increased the percentage of current traces showing no single Na+ channel openings in response to depolarizing voltage-clamp pulses. Moreover, the average of current traces containing single Na+ channel openings was essentially the same in control conditions and after treatment with DAG compounds. Removal of Na+ channel inactivation by the alkaloid batrachotoxin prevented the attenuation of Na+ currents by PKC activation via DAGs. Taken together, these data strongly suggest that PKC-induced attenuation of Na+ currents is linked to an enhancement of Na+ channel inactivation. This attenuation is caused by an increase in the number of Na+ channels inactivating directly from the closed state(s). This inactivation pathway represents a simple and efficient physiological mechanism by which PKC activation might modulate the electrical activity of excitable cells.
authors.affiliation: Department of Physiology, Loyola University Medical Center, Maywood, Ill 60153, USA.
authors.forename: C M
authors.initials: CM
authors.lastname: Godoy
authors.forename: S
authors.initials: S
authors.lastname: Cukierman
mesh_terms: D000818:Animals; D004075:Diglycerides / Q000494:pharmacology*; D004789:Enzyme Activation / Q000187:drug effects; D008564:Membrane Potentials; D051379:Mice; D018408:Patch-Clamp Techniques; D011493:Protein Kinase C / Q000378:metabolism*; D015222:Sodium Channels / Q000187:drug effects / Q000502:physiology*
chemical_list: D004075:Diglycerides; D015222:Sodium Channels; D011493:Protein Kinase C