AJP - Cell Physiology, Vol 259, Issue 5 C723-C726, Copyright © 1990 by American Physiological Society
Effect of oxygen tension on catecholamine-induced formation of cAMP and on swelling of carp red blood cells
A. Salama and M. Nikinmaa
Department of Zoology, University of Helsinki, Finland.
We studied the effects of beta-adrenergic stimulation on the formation of
adenosine 3',5'-cyclic monophosphate (cAMP) and on the cell volume in carp
red blood cells in normoxia (PO2 = 150 mmHg) and hypoxia (PO2 = 8 mmHg).
Accumulation of cAMP was the prerequisite for adrenergic cell swelling.
Cell swelling was induced by beta-agonists, forskolin, and 8-bromo-cAMP.
The amount of cAMP required for adrenergic swelling was minimal; swelling
was observed at cAMP concentrations greater than 100 nM. Maximal increase
in cell volume was observed at 200 nM cAMP. These values were independent
of both the oxygen tension and the beta-agonist used. Norepinephrine caused
the largest accumulation of cAMP, followed by isoproterenol and
epinephrine. At hypoxic conditions, the cAMP concentrations obtained after
stimulation with the natural catecholamines norepinephrine and epinephrine
were greater than at normoxic conditions. The catecholamines caused
appreciable cell swelling at lower concentrations in hypoxia than in
normoxia. Thus the number of beta-adrenergic receptors, and their inherent
ligand affinities, may be higher in hypoxic than in normoxic carp red blood
cells. Oxygen tension had a pronounced effect on the magnitude of the
adrenergic swelling. The maximal increase in cell volume was 5-7% in
hypoxia, whereas in normoxia it was only approximately 2%. This was not due
to differences in cAMP formation, but possibly to a greater activity of the
Na(+)-H+ exchanger in hypoxic than in normoxic conditions.
