Inhibition of voltage-gated K channels in synaptosomes by sn-1,2-dioctanoylglycerol, an activator of protein kinase C.
Tracer efflux studies were used to determine the effect of activation of protein kinase C on K channel function in rat brain synaptosomes. Hippocampal synaptosomes were treated with sn-1,2-dioctanoylglycerol (diC8), a synthetic diacylglycerol (DG) analog that activates protein kinase C. DiC8 inhibited depolarization-induced 86Rb efflux through voltage-gated K channels but did not affect the component of efflux corresponding to Ca-activated K channels. In time-course experiments, diC8 inhibited two components of 86Rb efflux: efflux through a rapidly inactivating, voltage-gated K channel (responsible for the "A" current) and that through a slowly inactivating, voltage-gated K channel (believed to be the "delayed rectifier"). Experiments with specific blockers of these voltage-gated K channels supported this observation. Inhibition of K-stimulated 86Rb efflux by diC8 was time dependent: at least 15 sec of preincubation was required before the effect could be observed. The effect of diC8 was concentration dependent: 50 microM diC8 produced a half-maximal inhibition of K-stimulated 86Rb efflux. The idea that the inhibition of synaptosome K channels by diC8 resulted from activation of C kinase was supported by pharmacological evidence. The action of diC8 was mimicked by 1-oleoyl-2-acetylglycerol, another DG analog that activates protein kinase C, but not by deoxy-diC8, a DG analog that does not activate C kinase. Inhibition of C kinase by sphingosine or H-7 prevented the diC8 effect. These studies demonstrate that synaptosomes are a good model in which to study modulation of mammalian CNS K channels.(ABSTRACT TRUNCATED AT 250 WORDS)
Colby
K A
KA
Department of Physiology, University of Maryland School of Medicine, Baltimore 21201.
Blaustein
M P
MP
D000818:Animals; D002118:Calcium / Q000494:pharmacology; D004075:Diglycerides / Q000494:pharmacology*; D004594:Electrophysiology; D004789:Enzyme Activation; D005260:Female; D005989:Glycerides / Q000494:pharmacology*; D009994:Osmolar Concentration; D011188:Potassium / Q000494:pharmacology; D015221:Potassium Channels / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology; D011493:Protein Kinase C / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D012413:Rubidium / Q000378:metabolism; D013329:Structure-Activity Relationship; D013574:Synaptosomes / Q000187:drug effects / Q000378:metabolism*; D013997:Time Factors
D004075:Diglycerides; D005989:Glycerides; D015221:Potassium Channels; C044295:1,2-dioctanoylglycerol; D011493:Protein Kinase C; D012413:Rubidium; D011188:Potassium; D002118:Calcium