Expression of the Subtype 1A Dopamine Receptor in the Rat Heart

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Abstract
The subtype 1A dopamine receptor (D 1A ) has recently been detected in the rat kidney. In the present study using light microscopic immunohistochemistry, electron microscopic immunocytochemistry, and in situ amplification of mRNA, we demonstrate the D 1A receptor in Sprague-Dawley and Wistar-Kyoto rat hearts. For immunohistochemistry and immunocytochemistry, anti-peptide polyclonal antibodies were directed toward amino acid sequences of the third extracellular and intracellular domains of the native receptor. Selectivity was validated by recognition of the D 1A receptor expressed in stably transfected LTK − cells. D 1A receptor mRNA was detected with a novel transcription-based isothermal in situ amplification system as well as with reverse transcription–polymerase chain reaction. D 1A receptor protein was distributed throughout the atrium and ventricular myocardium. Preimmune and preabsorption controls were negative. Electron microscopic immunocytochemistry using the protein A gold method demonstrated the D 1A receptor along the cellular membranes of coronary smooth muscle cells and ventricular myocytes and in the myosin thick filaments and M-lines. D 1A receptor mRNA was present in coronary vessels and myocardium in amplified but not in unamplified sections. Western blot analysis showed specific D 1A bands in transfected LTK − cells and the atrium but not in nontransfected LTK − cells and the ventricle. The selective D1-like receptor agonist SKF38393 stimulated adenylyl cyclase in ventricular myocardial plasma membranes in a dose-related fashion, and the response was abolished by the selective D1-like receptor antagonist SCH23390 . These results demonstrate that the D 1A receptor gene and protein are expressed in normal rat heart. The physiological and pathophysiological roles and predominant cell signaling mechanism or mechanisms of this receptor remain to be determined.