L-type calcium channel activity regulates sodium channel levels in rat pituitary GH3 cells.
1. The effects of chronic pharmacological modulation of L-type Ca2+ channel activity on the cell surface expression of Na+ channels were examined in GH3 cells. 2. Prolonged inhibition (4-5 days) of L-channels with nimodipine caused a 50-60 % decrease in the peak amplitude of whole-cell Na+ currents recorded with the patch-clamp technique. On the contrary, prolonged exposure to the L-channel agonist Bay K 8644 induced an approximately 2.5-fold increase in peak Na+ current. In both cases, there were only minor changes in cell capacitance and no significant changes in Na+ channel gating properties. 3. Measurements of the specific binding of radiolabelled saxitoxin to intact cells showed that nimodipine treatment reduced the number of cell surface Na+ channels, whereas treatment with Bay K 8664 produced the opposite effect. The dual regulation of Na+ channel abundance explained the mentioned changes in Na+ current amplitude. 4. Plasma membrane Na+ channels had a half-life of approximately 17 h both in control cells and in cells treated with Bay K 8644, as estimated from the rate of decay of peak Na+ current after inhibition of protein synthesis with cycloheximide. Actinomycin D, an inhibitor of gene transcription, and also cycloheximide, occluded the stimulatory effect of Bay K 8644 on Na+ current density when measured over a 24 h period. 5. These findings indicate that the entry of Ca2+ through L-type channels influences in a positive way the number of functional Na+ channels in GH3 cells, and suggest that Ca2+ influx stimulates either Na+ channel gene expression or the expression of a regulatory protein that promotes translocation of pre-assembled Na+ channels into the plasma membrane.
Monjaraz
E
E
Department of Physiology, Biophysics and Neuroscience, Center for Research and Advanced Studies, National Polytechnic Institute, Mexico City, DF 07000, Mexico.
Navarrete
A
A
Lopez-Santiago
L F
LF
Vega
A V
AV
Arias-Montaño
J A
JA
Cota
G
G
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000818:Animals; D002120:Calcium Channel Agonists / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020746:Calcium Channels, L-Type / Q000502:physiology*; D002460:Cell Line; D003513:Cycloheximide / Q000494:pharmacology; D003609:Dactinomycin / Q000494:pharmacology; D004594:Electrophysiology; D015640:Ion Channel Gating / Q000187:drug effects; D009553:Nimodipine / Q000494:pharmacology; D019384:Nucleic Acid Synthesis Inhibitors / Q000494:pharmacology; D010902:Pituitary Gland / Q000166:cytology / Q000378:metabolism*; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D051381:Rats; D012530:Saxitoxin / Q000378:metabolism; D015222:Sodium Channels / Q000378:metabolism* / Q000502:physiology; D014158:Transcription, Genetic / Q000187:drug effects
D002120:Calcium Channel Agonists; D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D019384:Nucleic Acid Synthesis Inhibitors; D011500:Protein Synthesis Inhibitors; D015222:Sodium Channels; D003609:Dactinomycin; D012530:Saxitoxin; D009553:Nimodipine; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D003513:Cycloheximide