Depolarization regulates adrenal preproenkephalin mRNA.

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Abstract
The regulation of neuropeptide gene expression has been investigated by using rat adrenal medullae grown in explant culture. After 3 days in culture the (now denervated) explants exhibited a 10-fold increase in leucine-enkephalin (leu-EK) content. Inhibition of protein synthesis with cycloheximide completely blocked the rise, whereas inhibition of RNA synthesis with actinomycin D or alpha-amanitin inhibited the increase by 50%. Inhibition of DNA synthesis with 1-beta-D-arabinofuranosylcytosine (cytosine arabinoside) had no discernible effect. To determine whether the rise in leu-EK was associated with an increase in specific mRNA coding for the opiate peptide precursor, blot hybridization analysis was performed. A single species of preproenkephalin mRNA was detected after various culture periods. The amount of mRNA increased 34-fold after 2 days in culture and 74-fold after 4 days. Consequently, the rise in mRNA levels preceded the increase in the amount of leu-EK. Depolarization of the adrenal medullae with either elevated potassium or veratridine, which prevents leu-EK accumulation, inhibited the increase in the amount of preproenkephalin mRNA. Moreover, the effect of veratridine was blocked by tetrodotoxin, suggesting that transmembrane sodium ion influx affects the increase in the amount of message. Our studies suggest that elevation of leu-EK in explanted (denervated) medullae is associated with increased amounts of mRNA coding for the peptide precursor and that these processes can be regulated by depolarization.