AJP - Cell Physiology, Vol 256, Issue 2 C219-C225, Copyright © 1989 by American Physiological Society
Glucocorticoid receptor activation in isolated perfused rat hearts
S. M. Czerwinski, E. E. McKee and R. C. Hickson
Department of Physical Education, University of Illinois, Chicago 60680.
The formation of unactivated and activated glucocorticoid receptor
complexes was studied in intact, isolated, perfused rat hearts in the
presence of [3H]triamcinolone acetonide. Receptor activation, as quantified
by the DNA-cellulose-binding assay, began to increase within 30 s of
perfusion and reached a final steady-state level (t 1/2 = 4.6 min) with 46%
of the steroid-receptor complexes bound to DNA-cellulose. With the use of a
linear potassium phosphate (KP) gradient (5-400 mM), unactivated receptors
eluted from DEAE-cellulose anion exchange columns at approximately 250 mM
KP. Two activated receptor forms appeared, which eluted either in the wash
fraction (binder IB) or between 50 and 100 mM KP (binder II) and occurred
with half times of 1.3 and 2.7 min, respectively. Postperfusion cytosol
preparation did not markedly influence the results as receptor binding was
reduced by 10% or less when a 100-fold excess of unlabeled triamcinolone
acetonide was included in the homogenizing buffer. We conclude from these
results that glucocorticoids are able to exert a direct effect on the heart
through binding to their own receptor in the absence of endogenous
hormones. The time dependency of receptor activation supports a
physiological role for this process. However, activation rates, determined
from conformational changes associated with altered DEAE-cellulose elution
profiles and appearance of activated receptor forms, occur earlier and may
not be coordinated with the rate of activation as quantified by
DNA-cellulose binding.
