DIFFERENTIAL REGULATION OF PHENYLETHANOLAMINE N-METHYLTRANSFERASE EXPRESSION IN 2 DISTINCT SUBPOPULATIONS OF BOVINE CHROMAFFIN CELLS

Chromaffin cells were isolated from bovine adrenal glands and fraction ated into two distinct subpopulations by density gradient centrifugati on on Percoll, Cells in the more dense fraction stored epinephrine (E) as their predominant catecholamine (81% of total catecholamines), con tained high levels of phenylethanolamine N-methyltransferase (PNMT) ac tivity, and exhibited intense PNMT immunoreactivity. This population o f chromaffin cells was termed the E-rich cell population, Cells in the less dense fraction, the norepinephrine (NE)-rich cell population, st ored predominantly NE (75% of total catecholamines). Although the NE-r ich cells had only 3% as much PNMT activity as did the E-rich cells, 2 0% of the NE-rich cells were PNMT immunoreactive. This suggested that the PNMT-positive cells in the NE-rich cell cultures contained less PN MT per cell than did E-rich cells and may not be typical adrenergic ce lls, The regulation of PNMT mRNA levels and PNMT activity in primary c ultures of E-rich and NE-rich cells was compared. At the time the cell s were isolated, PNMT mRNA levels in NE-rich cells were similar to 20% of those in E-rich cells; within 48 h in culture, PNMT mRNA in both p opulations declined to almost undetectable levels, Treatment with dexa methasone increased PNMT mRNA levels and PNMT activity in both populat ions. In E-rich cells, dexamethasone restored PNMT mRNA to the level s een in freshly isolated cells and increased PNMT activity twofold, In NE-rich cells, dexamethasone increased PNMT mRNA to levels twice those found in freshly isolated cells and increased PNMT activity sixfold, Cycloheximide blocked the effects of dexamethasone on PNMT mRNA expres sion in NE-rich cells but had little effect in E-rich cells. Angiotens in II, forskolin, and phorbol 12,13-dibutyrate elicited large increase s in PNMT mRNA levels in E-rich cells but had no effect in NE-rich cel ls, Our data suggest that PNMT expression is regulated differently in the two chromaffin cell subpopulations.