title: Temperature-dependent regulation of d-cis-[3H]diltiazem binding to Ca2+ channels by 1,4-dihydropyridine channel agonists and antagonists.
abstract: The binding of the Ca2+-channel blocker d-cis-[3H]diltiazem to guinea pig skeletal muscle microsomes is temperature-dependent. At 2 degrees C the KD is 39 nM and Bmax is 11 pmol/mg protein. The binding is fully reversible (K -1 = 0.02 min -1). The binding sites discriminate between the diastereoisomers l- and d-cis-diltiazem, reconize verapamil, gallopamil and tiapamil, and are sensitive to La3+-inhibition. At 30 degrees C the KD is 37 nM and the Bmax is 2.9 pmol/mg protein. D-cis-diltiazem-labelling is regulated by the 1,4-dihydropyridine Ca2+-channel blockers and a novel Ca2+-channel activator in a temperature-dependent manner. At 30 degrees C an enhancement of d-cis-diltiazem binding by the channel blockers is observed. This is attributed to a Bmax increase. EC50-values for enhancement and the maximal enhancement differ for the individual 1,4-dihydropyridines. At 2 degrees C 1,4-dihydropyridines inhibit d-cis-[3H]diltiazem binding. This is attributed to a Bmax decrease. We have directly labelled one of the drug receptor sites within the Ca2+-channel which can allosterically interact with the 1,4-dihydropyridine binding sites.
mesh_terms: D000818:Animals; D001552:Benzazepines / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D004095:Dihydropyridines; D004110:Diltiazem / Q000378:metabolism*; D006168:Guinea Pigs; D007473:Ion Channels / Q000378:metabolism*; D007700:Kinetics; D008861:Microsomes / Q000378:metabolism*; D009132:Muscles / Q000378:metabolism*; D011725:Pyridines / Q000494:pharmacology*; D013237:Stereoisomerism; D013329:Structure-Activity Relationship; D013696:Temperature
chemical_list: D001552:Benzazepines; D002121:Calcium Channel Blockers; D004095:Dihydropyridines; D007473:Ion Channels; D011725:Pyridines; C038806:1,4-dihydropyridine; D004110:Diltiazem; D002118:Calcium