MOLECULAR MECHANISMS OF REGULATORY ACTION OF ADRENERGIC RECEPTOR AGONISTS ON
FUNCTIONAL ACTIVITY OF ADENYLYL CYCLASE SIGNALING SYSTEM OF THE CILIATES DILEPTUS ANSER AND
TETRAHYMENA PYRIFORMIS
A. O. Shpakov, 1 K. V. Derkach, 1 Z. I. Uspenskaya, 2
E. A. Shpakova, 1 L. A. Kuznetsova, 1 S. A. Plesneva, 1 M. N. Pertseva 1
1 I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry RAS, and
2 Institute of Cytology RAS, St. Petersburg, Russia;
Adenylyl cyclase signaling system (ACS) of the higher eukaryotes involves the following main components: receptor,
heterotrimeric G protein, adenylyl cyclase (AC), and protein kinase A. At present, these components have been found in cells of different
species of the lower eukaryotes. Hence, the signal transduction through ACS of unicellular eukaryotes may have some features in
common with those of the higher eukaryotes. We showed earlier that agonists of adrenergic receptors (ARs) regulate AC activity of ciliates
Dileptus anser and Tetrahymena pyriformis. The aim of this work was to study molecular mechanisms of AR ligand action on
the functional activity of different components of ACS of the ciliates. It has been shown that β-AR antagonist
[3H]-dihydroalprenolol binds membranes of the ciliates with a comparatively lower affinity than those of the higher eukaryotes
(Kd for D. anser was 13.4 nM, for T. pyriformis - 21 nM). β-AR ligands - agonist (-)-isoproterenol and
antagonists propranolol and atenolol in competition manner displace [3H]-dihydroalprenolol with IC50
that are 10-100 times higher than corresponding IC50 of β-AR of the higher eukaryotes. In the presence of GTP,
the right shift of competition curves of [3H]-dihydroalprenolol displacement by isoproterenol was obtained, being most
considerable in the case of D. anser. Adrenaline and isoproterenol in a dose-dependent manner stimulated GTP-binding in cell
cultures of D. anser and T. pyriformis. Suramin (10-5 M), the inhibitor of heterotrimeric G proteins, completely
blocked effects of these hormones. In D. anser culture, adrenaline and isoproterenol in a dose-dependent manner, stimulated AC
activity, and its stimulating effects in the presence of β-AR blockers vanished (propranolol) or decreased to a great extent (atenolol).
At the same time the effects were unchanged in the presence of α2-AR antagonists yohimbine and idazoxan.
These data show the involvement of G protein-coupled β-AR in signal transduction induced by AR agonists in D. anser cells.
In cell culture of T. pyriformis isoproterenol weakly stimulated AC activity, and its effect was completely blocked by β-AR blockers.
Adrenaline in T. pyriformis cells in a dose-dependent manner inhibited AC activity. Inhibiting effect of hormone was decreased in the
presence of α2-AR blockers. On the basis of the obtained data we concluded that adrenaline in T. pyriformis cells
inhibited AC activity through G protein-coupled receptor, being close to α2-AR of vertebrate animals.
Key words: adenylyl cyclase, adenylyl cyclase signaling system, adrenaline, adrenergic receptor, isoproterenol,
ciliatae, the lower eukaryotes, Dileptus anser, Tetrahymena pyriformis
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