Calmodulin-like activity and calcium-dependent phosphodiesterase in purified cells of the rat zona glomerulosa and zona fasciculata.

Abstract

We have studied calmodulin (CaM)-like activity and calcium (Ca++)-regulated phosphodiesterase (PDE) activity in cells from the rat adrenal zona glomerulosa (ZG) and zona fasciculata (ZF). Boiled cell sonicates from the ZG and ZF activated CaM-deficient PDE in a dose-dependent fashion by 2.0- to 2.3-fold. The properties of this stimulatory factor were similar to those of authentic CaM in a number of respects: 1) both activated CaM-deficient PDE at micromolar calcium concentrations; 2) both eluted at similar ionic strengths on DEAE-cellulose ion exchange chromatography; 3) the activation of CaM-dependent PDE activity was blocked by the CaM inhibitor trifluoperazine in both cases; and 4) Ca++-dependent activation of PDE was totally inhibited by an excess of EGTA. Boiled sonicates of cells from the ZG and ZF contained 366 +/- 53 and 882 +/- 69 ng/10(6) cells of CaM-like activity (P less than 0.01), respectively, as determined by comparison with activation of CaM-deficient PDE by a known amount of authentic rat CaM. The CaM contents of the ZG and ZF, determined by RIA, were 1050 +/- 35 and 1760 +/- 112 ng/10(6) cells, respectively (P less than 0.01). Under identical conditions, there were 4 times more cAMP and cGMP PDE activities in the ZG than in the ZF. EGTA (1 mM) or trifluoperazine (10(-4) M) inhibited 20% of PDE activity in ZG, and the addition of excess Ca++ (1.1 mM) restored about 50% of the EGTA-inhibited PDE activity. Maximal PDE activity in each cell type eluted at 0.25 M NaCl using DEAE-cellulose ion exchange chromatography. This activity was partially inhibited by EGTA. Moreover, each cell type contained CaM-like activity that migrated at 0.25 M NaCl. The ZF contained a second peak of CaM that migrated at 0.35 M NaCl. Boiled sonicates of the ZF and ZG, on the other hand, each had a single peak of CaM-like activity, which eluted from DEAE-cellulose at 0.28-0.29 M NaCl, similar to that of pure CaM from rat testes. Thus, these experiments demonstrate the presence of a heat-stable activator of CaM-dependent PDE activity in the ZG and ZF that is similar by a number of criteria to purified CaM. The presence of CaM and a Ca++-dependent PDE in the adrenal suggests that the effects of Ca++ on adrenal function might be mediated, in part, by this or other CaM-regulated enzymes.