EXPRESSION OF THE SUBTYPE 1A DOPAMINE-RECEPTOR IN THE RAT-HEART

The subtype 1A dopamine receptor (D-1A) has recently been detected in the rat kidney. In the present study using light microscopic immunohis tochemistry, electron microscopic immunocytochemistry, and in situ amp lification of mRNA, we demonstrate the D-1A receptor in Sprague-Dawley and Wistar-Kyoto rat hearts. For immunohistochemistry and immunocytoc hemistry, anti-peptide polyclonal antibodies were directed toward amin o acid sequences of the third extracellular and intracellular domains of the native receptor. Selectivity was validated by recognition of th e D-1A receptor expressed in stably transfected LTK(-) cells. D-1A rec eptor mRNA was detected with a novel transcription-based isothermal in situ amplification system as well as with reverse transcription-polym erase chain reaction. D-1A receptor protein was distributed throughout the atrium and ventricular myocardium. Preimmune and preabsorption co ntrols were negative. Electron microscopic immunocytochemistry using t he protein A gold method demonstrated the D-1A receptor along the cell ular membranes of coronary smooth muscle cells and ventricular myocyte s and in the myosin thick filaments and M-lines. D-1A receptor mRNA wa s present in coronary vessels and myocardium in amplified but not in u namplified sections. Western blot analysis showed specific D-1A bands in transfected LTK(-) cells and the atrium but not in nontransfected L TK(-) 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 dem onstrate that the D-1A receptor gene and protein are expressed in norm al rat heart. The physiological and pathophysiological roles and predo minant cell signaling mechanism or mechanisms of this receptor remain to be determined.