title: Subcellular distribution of [3H]nitrendipine binding in smooth muscle.
abstract: Distribution of specific binding sites for [3H]nitrendipine was studied in subcellular fractions isolated from rat gastric fundus smooth muscle and from rat myometrium. There was an excellent correlation between the distribution of [3H]nitrendipine binding determined at the nitrendipine concentrations of 0.138 and 1.38 nM, and the distribution of the plasma membrane markers K+-activated ouabain-sensitive p-nitrophenylphosphatase, 5'-nucleotidase, phosphodiesterase I, and Mg-ATPase, but not between the mitochondrial markers cytochrome c, oxidase, succinate-dependent cytochrome c reductase, or rotenone-insensitive NADH-dependent cytochrome c reductase or the putative endoplasmic reticulum marker NADPH-dependent cytochrome c reductase. The binding occurred with high affinity and with a similar (0.097-0.146 nM) equilibrium dissociation constant to all the fractions, even though the density of binding sites varied and was highest in the plasma membrane marker-enriched fractions. The maximal binding in the plasma membrane-enriched fraction from the rat gastric fundus smooth muscle was 0.43 +/- 0.04 pmol/mg, and in that from rat myometrium was 0.72 +/- 0.09 pmol/mg. Thus in the two smooth muscles studied the plasma membrane is the locus of the high affinity nitrendipine binding.
mesh_terms: D000818:Animals; D002121:Calcium Channel Blockers / Q000378:metabolism*; D015220:Calcium Channels; D002462:Cell Membrane / Q000378:metabolism; D005260:Female; D005748:Gastric Fundus / Q000378:metabolism; D007700:Kinetics; D009130:Muscle, Smooth / Q000378:metabolism*; D009215:Myometrium / Q000378:metabolism; D009543:Nifedipine / Q000031:analogs & derivatives* / Q000378:metabolism; D009568:Nitrendipine; D051381:Rats; D011919:Rats, Inbred Strains; D011978:Receptors, Nicotinic / Q000378:metabolism*; D013347:Subcellular Fractions / Q000378:metabolism
chemical_list: D002121:Calcium Channel Blockers; D015220:Calcium Channels; D011978:Receptors, Nicotinic; D009568:Nitrendipine; D009543:Nifedipine