Expression of multiple alpha-adrenoceptor isoforms in rat CCD.
In the rat cortical collecting duct (CCD), epinephrine inhibits vasopressin (AVP)-dependent water permeability and Na+ reabsorption. Although inhibition is reversed by the alpha2-adrenoceptor (AR) antagonist yohimbine, suggesting the epinephrine effect is primarily mediated by an alpha2-AR [C. T. Hawk, L. H. Kudo, A. J. Rouch, and J. A. Schafer. Am. J. Physiol. 265 (Renal Fluid Electrolyte Physiol. 34): F449-F460, 1993], there are also suggestions of an effect at an additional receptor, perhaps an alpha1-AR. For the present experiments, we used RT-PCR of total RNA extracted from 1 to 5 mm of microdissected CCDs from rat kidney to identify the alpha-AR isoforms expressed. Specific primers for the alpha2-ARs amplifying from the 6th transmembrane (TM) to the 3'-untranslated regions, revealed the presence of alpha2A and alpha2B. Western blot analysis also indicated the presence of alpha2B-AR at the protein level. Degenerate alpha1-AR primers that amplify from conserved regions of TM-1 to TM-5, as well as specific primers that amplify either the same region (alpha1B), the carboxy terminus (alpha1A), or within the third cytoplasmic loop (alpha1D), indicated the presence of all three alpha1-ARs. Measurement of transepithelial voltage in isolated perfused renal tubules indicated a small inhibitory effect mediated by alpha1-ARs. Although the functional effects of epinephrine on AVP-dependent transport processes appear to be mediated predominantly by an alpha2-AR, a small contribution to the overall alpha-AR effect may be due to simultaneous activation of an alpha1-AR.
Department of Physiology, Nephrology Training and Research Center, University of Alabama at Birmingham, Birmingham, Alabama 35294, USA.
T W
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Wilborn
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Sun
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Schafer
D000818:Animals; D001127:Arginine Vasopressin / Q000494:pharmacology; D017931:DNA Primers; D003900:Desoxycorticosterone / Q000494:pharmacology; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D005786:Gene Expression Regulation / Q000187:drug effects; D007672:Kidney Cortex / Q000378:metabolism*; D007685:Kidney Tubules, Collecting / Q000378:metabolism*; D008297:Male; D008564:Membrane Potentials; D010646:Phentolamine / Q000494:pharmacology; D010656:Phenylephrine / Q000494:pharmacology; D016133:Polymerase Chain Reaction; D011433:Propranolol / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D011942:Receptors, Adrenergic, alpha / Q000096:biosynthesis*; D018340:Receptors, Adrenergic, alpha-1 / Q000096:biosynthesis; D018341:Receptors, Adrenergic, alpha-2 / Q000096:biosynthesis; D015016:Yohimbine / Q000494:pharmacology
C547715:Adra1a protein, rat; C547721:Adra1d protein, rat; C547770:Adra2a protein, rat; C547773:Adra2b protein, rat; C547776:Adra2c protein, rat; D017931:DNA Primers; D011942:Receptors, Adrenergic, alpha; D018340:Receptors, Adrenergic, alpha-1; D018341:Receptors, Adrenergic, alpha-2; D001127:Arginine Vasopressin; D010656:Phenylephrine; D015016:Yohimbine; D003900:Desoxycorticosterone; D011433:Propranolol; D010646:Phentolamine