Coordinate and differential regulation of proenkephalin A and PNMT mRNA expression in cultured bovine adrenal chromaffin cells: responses to secretory stimuli.
The expression of proenkephalin A (ProEnk A) mRNA and phenylethanolamine N-methyltransferase (PNMT) mRNA in response to nicotine and to a number of secretagogues was examined in cultured bovine adrenal chromaffin cells. Prolonged incubation with nicotine (10 microM) resulted in a 2-fold increase in ProEnk A mRNA but had no significant effect on the level of PNMT mRNA. Similarly, prolonged stimulation with high K+ (56 mM) induced a time-dependent elevation in the level of ProEnk A mRNA reaching 4-fold basal level after 24 h incubation. By contrast, the level of PNMT mRNA was not changed by treatment with high K+. The increase in the level of ProEnk A mRNA by high K+ was abolished by the presence of 10 microM D600, a calcium channel blocker. Unlike the effects of high K+, treatment of the cells with the sodium channel activator veratridine significantly elevated the levels of both ProEnk A and PNMT mRNA. This increase in ProEnk A and PNMT mRNA levels was however less affected by D600. Stimulation of the cells with Ba2+ (1.1 mM) also stimulated the levels of ProEnk A and PNMT mRNA and this action required the presence of extracellular Ca2+. This was in contrast to the effect of Ba2+ in stimulating catecholamine secretion, which was inhibited by Ca2+ and enhanced in Ca2(+)-free buffer. The results of the present study indicate that membrane depolarization and entry of extracellular Ca2+ play an important role on the regulation of ProEnk A and PNMT mRNAs, in addition to their well-known actions on hormone secretion. Furthermore, these results suggest that the expression of ProEnk A mRNA and PNMT mRNA are under independent regulation in response to secretory stimulation.
Wan
D C
DC
Department of Biochemistry, University of Melbourne, Parkville, Vic. Australia.
Marley
P D
PD
Livett
B G
BG
D000313:Adrenal Medulla / Q000187:drug effects* / Q000378:metabolism; D000818:Animals; D001464:Barium / Q000494:pharmacology; D001483:Base Sequence; D002118:Calcium / Q000494:pharmacology; D002417:Cattle; D004745:Enkephalins / Q000096:biosynthesis* / Q000235:genetics; D005089:Exocytosis / Q000187:drug effects; D005786:Gene Expression Regulation / Q000187:drug effects*; D008564:Membrane Potentials / Q000187:drug effects; D008969:Molecular Sequence Data; D009538:Nicotine / Q000494:pharmacology; D010625:Phenylethanolamine N-Methyltransferase / Q000096:biosynthesis* / Q000235:genetics; D011498:Protein Precursors / Q000096:biosynthesis* / Q000235:genetics; D012333:RNA, Messenger / Q000096:biosynthesis*; D012636:Secretory Rate / Q000187:drug effects; D014701:Veratridine / Q000494:pharmacology
D004745:Enkephalins; D011498:Protein Precursors; D012333:RNA, Messenger; C029992:proenkephalin; D001464:Barium; D009538:Nicotine; D014701:Veratridine; D010625:Phenylethanolamine N-Methyltransferase; D002118:Calcium