Topography of 3H-DHA, 3H-QNB, 3H-Dopamine, and 3H-DAGO Binding Sites Distribution in the Central Part of the Sinoatrial Node in Rat Heart

The topography of distribution of ³H-dihydroalprenolol, ³H-quinucledinyl benzilate, ³H-dopamine, and ³H-DAGO binding sites in the central part of the sinoatrial node in rat heart was studied by autoradiography after electrophysiological identification of the dominant pacemaker region location. Receptor asymmetry between the lateral and median regions of the central part of the sinoatrial node was shown. The dominant pacemaker region lay in the lateral area of the sinoatrial node; the number of binding sites for all four ligands was minimum in it. The number of binding sites gradually increased in the cranial and caudal directions from the dominant pacemaker region along the sinoatrial node artery (more smoothly in the caudal direction). The relative densities of bindings sites for ³H-dihydroalprenolol and ³H-dopamine were higher in the lateral region compared to the perinodal working myocardium, while the densities for ³H-quinucledinyl benzilate and ³H-DAGO were virtually the same. The distribution of binding sites along the artery in the median region of the sinoatrial node was even for ³H-quinucledinyl benzilate and ³H-DAGO. For ³H-DAGO these parameters were close to those in the perinodal atrial myocardium, for ³H-quinucledinyl benzilate somewhat lower. Curves presenting the distribution of binding site densities for ³H-dihydroalprenolol and ³H-dopamine in the median region of the sinoatrial node were similar, with a pronounced peak in the region contralateral to the dominant pacemaker region, and significantly higher binding parameters compared to those for the perinodal atrial myocardium. The difference consisted in higher density of ³H-dopamine binding sites in the median region of the sinoatrial node in comparison with the lateral region. Binding activity was maximum in the wall of the sinoatrial node artery. The distribution of binding sites for ligands to the main autonomic nervous system neurotransmitters in the rat heart sinoatrial node is heterogeneous. __________ Translated from Byulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 140, No. 10, pp. 472–477, October, 2005