Proenkephalin A gene expression in bovine adrenal chromaffin cells is regulated by changes in electrical activity.
Concentrations of mRNA coding for the opioid peptide precursor proenkephalin A (mRNAENK) were measured in primary cultures of bovine adrenal chromaffin cells maintained in serum-free medium. Using a sensitive solution hybridization assay, an increase in mRNAENK levels from 45 to 300% above control with K+ (10-20 mM), Ba2+ (1 mM) and veratridine (5 microM) was found. The highest increase (300% above control) was obtained with the Na+ channel agonist veratridine. This effect was nearly abolished in the presence of the Na+ channel antagonist tetrodotoxin (TTX) (1 microM). Moreover, TTX partially inhibited the increase in mRNAENK levels caused by K+ (20 mM) depolarization (from 185 to 130% of control), but had no effect on the stimulation by Ba2+ (1 mM). The Ca2+ channel antagonists D600 (50 microM) verapamil (50 microM) and Co2+ (1 mM) inhibited the responses to either K+, Ba2+ or veratridine, whereas the Ca2+ channel agonist Bay K 8644 (0.1 microM) potentiated the effect of 20 mM K+ from 185 to 230% of control. The K+-induced increase in the mRNAENK levels was associated with an increase of immunoreactive proenkephalin A-derived peptides in both tissue and medium, indicating an enhanced production of opioid peptides. These results suggest that membrane depolarization may play an important role in the regulation of proenkephalin A gene expression in bovine adrenal chromaffin cells. It may represent a mode by which substances acting directly on Na+ or Ca2+ channels may modulate the regulation of proenkephalin A mRNA biosynthesis and opioid peptide production.
D000313:Adrenal Medulla / Q000502:physiology*; D000818:Animals; D002417:Cattle; D002478:Cells, Cultured; D004553:Electric Conductivity / Q000187:drug effects; D004745:Enkephalins / Q000032:analysis / Q000235:genetics*; D005796:Genes / Q000187:drug effects; D007473:Ion Channels / Q000502:physiology; D009693:Nucleic Acid Hybridization; D011498:Protein Precursors / Q000032:analysis / Q000235:genetics*; D012333:RNA, Messenger / Q000235:genetics; D011863:Radioimmunoassay; D012964:Sodium / Q000378:metabolism; D013779:Tetrodotoxin / Q000494:pharmacology; D014158:Transcription, Genetic / Q000187:drug effects; D014701:Veratridine / Q000494:pharmacology
D004745:Enkephalins; D007473:Ion Channels; D011498:Protein Precursors; D012333:RNA, Messenger; C029992:proenkephalin; D013779:Tetrodotoxin; D014701:Veratridine; D012964:Sodium