Multiple effects of protein kinase C activators on Na+ currents in mouse neuroblastoma cells.
The effects of externally applied different protein kinase C (PKC) activators on Na+ currents in mouse neuroblastoma cells were studied using the perforated-patch (nystatin-based) whole cell voltage clamp technique. Two diacylglycerol-like compounds, OAG (1-oleoyl-2-acetyl-sn-glycerol), and DOG (1-2-dioctanoyl-rac-glycerol) attenuated Na+ currents without affecting the time course of activation or inactivation. The reduction in Na+ current amplitude caused by OAG or DOG was dependent on membrane potential, being more intense at positive voltages. The steady-state activation curve was also unaffected by these substances. However, both OAG and DOG shifted the steady-state inactivation curve of Na+ currents to more hyperpolarized voltages. Surprisingly, phorbol esters did not affect Na+ currents. Cis-unsaturated fatty acids (linoleic, linolenic, and arachidonic) attenuated Na+ currents without modifying the steady-state activation. As with DOG and OAG, cis-unsaturated fatty acids also shifted the steady-state inactivation curve to more negative voltages. Interestingly, inward currents were more effectively attenuated by cis-fatty acids than outward currents. Oleic acid, also a cis-unsaturated fatty acid, enhanced Na+ currents. This enhancement was not accompanied by changes in kinetic or steady-state properties of currents. Enhancement of Na+ currents caused by oleate was voltage dependent, being stronger at negative voltages. The inhibitory or stimulatory effects caused by all PKC activators on Na+ currents were completely prevented by pretreating cells with PKC inhibitors (calphostin C, H7, staurosporine or polymyxin B). By themselves, PKC inhibitors did not affect membrane currents. Trans-unsaturated or saturated fatty acids, which do not activate PKC's, did not modify Na+ currents. Taken together, the experimental results suggest that PKC activation modulates the behavior of Na+ channels by at least three distinct mechanisms. Because qualitatively different results were obtained with different PKC activators, it is not clear how Na+ currents would respond to activation of PKC under physiological conditions.
Godoy
C M
CM
Department of Physiology, Loyola University Medical Center, Maywood, Illinois 60153.
Cukierman
S
S
D000818:Animals; D004075:Diglycerides / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D005227:Fatty Acids / Q000494:pharmacology; D005231:Fatty Acids, Unsaturated / Q000494:pharmacology; D051379:Mice; D009447:Neuroblastoma / Q000378:metabolism; D010703:Phorbol Esters / Q000494:pharmacology; D011493:Protein Kinase C / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*; D015222:Sodium Channels / Q000187:drug effects / Q000378:metabolism; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000378:metabolism
D004075:Diglycerides; D005227:Fatty Acids; D005231:Fatty Acids, Unsaturated; D010703:Phorbol Esters; D015222:Sodium Channels; C044295:1,2-dioctanoylglycerol; C038237:1-oleoyl-2-acetylglycerol; D012964:Sodium; D011493:Protein Kinase C