title: Muscarinic receptors and responses in intact embryonic chick atrial and ventricular heart cells.
abstract: We have studied muscarinic acetylcholine (ACh) receptors in intact atrial and ventricular heart cells dissociated from 8-day chick embryos and maintained in sparse cell cultures. Two specific antagonists, [3H]quinuclidinyl benzilate (QNB) and [3H]N-methyl scopolamine (NMS), bind to surface sites with high affinity (Kds congruent to 40 and 400 pM, respectively). The concentration of [3H]QNB sites in ventricular cell cultures (460 fmole/mg protein) was comparable to the concentration of sites in atrial cultures (420 fmole/mg protein). The same result was obtained with [3H]NMS. Autoradiography following incubation in saturating concentrations of [3H]QNB shows that nearly all of the atrial and ventricular myocytes were labeled and that the distribution of grains over individual cells was uniform. The mean binding site density was 109/micron2 for atrial cells and 117/micron2 for ventricular cells. In contrast to the antagonist binding results, microelectrode recordings from individual myocytes or from small clusters of cells showed that many more atrial myocytes (89%) were sensitive to 10(-4) M carbachol than were ventricular myocytes (26%). Saline extract of embryonic brain tissue added to the culture medium did not alter the number or distribution of ligand binding sites but it produced a 2.6-fold increase in the number of carbachol-sensitive ventricular cells.
mesh_terms: D000818:Animals; D001921:Brain / Q000502:physiology; D002217:Carbachol / Q000494:pharmacology; D002478:Cells, Cultured; D002642:Chick Embryo; D006321:Heart / Q000187:drug effects / Q000196:embryology*; D006325:Heart Atria / Q000196:embryology; D006352:Heart Ventricles / Q000196:embryology; D009206:Myocardium / Q000166:cytology / Q000378:metabolism; D019832:N-Methylscopolamine; D011813:Quinuclidinyl Benzilate / Q000378:metabolism; D011976:Receptors, Muscarinic / Q000378:metabolism*; D012602:Scopolamine Derivatives / Q000378:metabolism; D014018:Tissue Distribution; D014020:Tissue Extracts / Q000494:pharmacology
chemical_list: D011976:Receptors, Muscarinic; D012602:Scopolamine Derivatives; D014020:Tissue Extracts; D011813:Quinuclidinyl Benzilate; D002217:Carbachol; D019832:N-Methylscopolamine