title: Voltage-dependent effects of YC-170, a dihydropyridine calcium channel modulator, in cardiovascular tissues.
abstract: Voltage-dependent effects of YC-170, a putative calcium channel activator, were examined and compared with those of Bay K 8644 in isolated guinea-pig cardiac tissues and rabbit aortae. In guinea-pig left atria superfused with a normal bathing solution (4 mmol/l K+), both YC-170 (10 mumol/l) and Bay K 8644 (1 mumol/l) produced a positive inotropic action accompanied by a prolongation of action potential durations (APDs). In normally-polarized guinea-pig papillary muscles Bay K 8644 increased force of contraction (fc) and APDs. However, YC-170 failed to increase fc in spite of a slight prolongation of APDs. In papillary muscles partially depolarized by 25 mmol/l K+ solution, Bay K 8644 enhanced the electrically-induced slow action potentials and contractile force. In contrast with Bay K 8644, YC-170 significantly depressed the slow action potentials and decreased fc. YC-170 also showed the depressant action on the slow action potentials induced by isoproterenol (0.1 mumol/l), histamine (3 mumol/l) and tetraethylammonium (10 mmol/l) plus high Ca2+ (4 mmol/l). In sinoatrial node cells of guinea-pig right atria Bay K 8644 produced a positive chronotropic action with increases in the maximum rate of rise (Vmax) and action potential amplitude (APA), whereas YC-170 produced a negative chronotropic action with decreases in Vmax and APA. In the rabbit aortic strips preincubated with bathing solution containing various concentrations of K+ (15, 20, 30 and 40 mmol/l), Bay K 8644 produced concentration-dependent contractions in a range of concentrations up to 0.3 mumol/l. However, when the concentration exceeded 1 mumol/l, Bay K 8644 caused a slight relaxation, irrespective of the K+ concentrations of bathing solution. YC-170 in concentrations of 10 and 30 mumol/l contracted the aortic strips placed in 5.9 or 15 mmol/l K+ bathing solution, but caused relaxation in 30 or 40 mmol/l K+ bathing solution. These results suggest that YC-170 is a dihydropyridine calcium channel modulator which behaves as a Ca2+ channel agonist in tissues of high membrane potentials, but as a Ca2+ channel antagonist in tissues of low membrane potentials.
mesh_terms: D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D002319:Cardiovascular System / Q000187:drug effects*; D005260:Female; D006168:Guinea Pigs; D006321:Heart / Q000187:drug effects; D006632:Histamine / Q000494:pharmacology; D066298:In Vitro Techniques; D007473:Ion Channels / Q000187:drug effects*; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D009130:Muscle, Smooth / Q000187:drug effects; D009543:Nifedipine / Q000031:analogs & derivatives* / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D011817:Rabbits; D012849:Sinoatrial Node / Q000187:drug effects; D013757:Tetraethylammonium Compounds / Q000494:pharmacology
chemical_list: D007473:Ion Channels; D013757:Tetraethylammonium Compounds; C046721:YC 170; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D006632:Histamine; D009543:Nifedipine; D007545:Isoproterenol; D011188:Potassium