Expression of multiple alpha-adrenoceptor isoforms in rat ccd.
Wilborn, Teresa W., Duo Sun, and James A. Schafer.
Departments of Physiology and Biophysics, Nephrology Training and
Research Center, University of Alabama at Birmingham, Birmingham, AL
35294
APStracts 5:0077F, 1998.
In the rat CCD, epinephrine inhibits vasopressin (AVP) -dependent
water permeability and Na+ reabsorption. Although inhibition is
reversed by the a2 adrenoceptor (AR) antagonist yohimbine, suggesting
the epinephrine effect is primarily mediated by an a2 AR (Hawk et
al., Am J Physiol 265:F449, 1993), there are also suggestions of an
effect at an additional receptor, perhaps an a1 AR. The present
experiments used RT/PCR of total RNA extracted from 1 to 5 mm of
microdissected cortical collecting ducts (CCD) from rat kidney to
identify the a AR isoforms expressed. Specific primers for the a2 ARs
amplifying from the 6th transmembrane (TM) to the 3-untranslated
regions, revealed the presence of a2A and a2B. Western blot analysis
also indicated the presence of a2B AR at the protein level.
Degenerate a1 AR primers that amplify from conserved regions of TM 1
to TM5, and specific primers that amplify either the same region
(a1B), the carboxy terminus (a1A), or within the third cytoplasmic
loop (a1D), indicated the presence of all three a1 ARs. Measurement
of transepithelial voltage in isolated perfused renal tubules
indicated a small inhibitory effect mediated by a1ARs. Although the
functional effects of epinephrine on AVP-dependent transport
processes appear to be mediated predominantly by an a2 AR, a small
contribution to the overall a AR effect may be due to simultaneous
activation of an a1 AR receptor.
Received 25 February 1997; accepted in final form 19 March 1998.
APS Manuscript Number F73-7.
Article publication pending Am. J. Physiol. (Renal Physiology).
ISSN 1080-4757 Copyright 1998 The American Physiological Society.
Published in APStracts on 24 April 1998