Internalization of voltage-dependent sodium channels in fetal rat brain neurons: a study of the regulation of endocytosis.
In fetal rat brain neurons, activation of voltage-dependent Na+ channels induced their own internalization, probably triggered by an increase in intracellular Na+ level. To investigate the role of phosphorylation in internalization, neurons were exposed to either activators or inhibitors of cyclic AMP- and cyclic GMP-dependent protein kinases, protein kinase C, and tyrosine kinase. None of the tested compounds mimicked or inhibited the effect of Na+ channel activation. An increase in intracellular Ca2+ concentration induced either by thapsigargin, a Ca(2+)-ATPase blocker, or by A23187, a Ca2+ ionophore, was unable to provoke Na+ channel internalization. However, Ca2+ seems to be necessary because both neurotoxin- and amphotericin B-induced Na+ channel internalizations were partially inhibited by BAPTA-AM. The selective inhibitor of Ca2+/calmodulin-dependent protein kinase II, KN-62, caused a dose-dependent inhibition of neurotoxin-induced internalization due to a blockade of channel activity but did not prevent amphotericin B-induced internalization. The rate of increase in Na+ channel density at the neuronal cell surface was similar before and after channel internalization, suggesting that recycling of internalized Na+ channels back to the cell surface was almost negligible. Pretreatment of the cells with an acidotropic agent such as chloroquine prevented Na+ channel internalization, indicating that an acidic endosomal/lysosomal compartment is involved in Na+ channel internalization in neurons.
Dargent
B
B
INSERM U374, Institut Jean Roche, Faculté de Médecine Secteur-Nord, Marseille, France.
Jullien
F
F
Couraud
F
F
D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine / Q000031:analogs & derivatives*; D000818:Animals; D001921:Brain / Q000166:cytology / Q000378:metabolism*; D002118:Calcium / Q000502:physiology; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000037:antagonists & inhibitors; D002738:Chloroquine / Q000494:pharmacology; D004594:Electrophysiology; D004705:Endocytosis; D007546:Isoquinolines / Q000494:pharmacology; D009474:Neurons / Q000378:metabolism*; D010879:Piperazines / Q000494:pharmacology; D011494:Protein Kinases / Q000502:physiology; D011505:Protein-Tyrosine Kinases / Q000502:physiology; D051381:Rats; D015222:Sodium Channels / Q000187:drug effects / Q000502:physiology*
D007546:Isoquinolines; D010879:Piperazines; D015222:Sodium Channels; C063302:KN 62; D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D002738:Chloroquine; D011494:Protein Kinases; D011505:Protein-Tyrosine Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D002118:Calcium