Garay A, Mattiazzi A
Acta Physiol Lat Am. 1982;32(4):295-302.
The present experiments were designed to analyze the effect of verapamil, nifedipine and isoproterenol on myocardial contractility (+dT/dtmax) and time to peak tension (TTP) and its dependence on extracellular calcium concentration (Ca2+). The experiments were performed on cat papillary muscles from reserpinized cats. At (Ca2+) 1.34 mM the negative inotropic effect of cumulative doses of verapamil and nifedipine and the positive inotropic effect of isoproterenol occurred associated with a significant and dose-dependent decrease in TTP. The decrease in TTP produced by calcium blockers was completely reversed by the addition of calcium in a close parallelism with the recovery in myocardial contractility: At (Ca2+) 1.34 mM; verapamil 10(-6)M significantly decreased TTP from 299 +/- 14 msec to 250 +/- 11 msec. At (Ca2+) 15 mM values for TTP were 285 +/- 7 msec (control) and 291 +/- 5 msec (verapamil). Nifedipine 5 X 10(-7) M decreased TTP from 343 +/- 20 msec to 246 +/- 4 msec (Ca 1.34 mM). Values of TTP at calcium 15 mM were 296 +/- 6 msec (control) and 300 +/- 17 msec (nifedipine). On the contrary, the significant decrease in TTP produced by isoproterenol 10(-5)M at (Ca2+) 1.34 from 266 +/- 14 msec to 222 +/- 14 msec was still present at (Ca2+) 15 mM: 233 +/- 8 msec (control) and 220 +/- 8 msec (isoproterenol). The results suggest that the decrease in TTP produced by calcium blockers and isoproterenol is mediated by different mechanisms.
本实验旨在分析维拉帕米、硝苯地平和异丙肾上腺素对心肌收缩力（+dT/dtmax）和达到最大张力的时间（TTP）的影响及其对细胞外钙浓度（Ca2+）的依赖性。实验在利血平化猫的乳头肌上进行。在（Ca2+）1.34 mM时，维拉帕米和硝苯地平累积剂量的负性肌力作用以及异丙肾上腺素的正性肌力作用伴随着TTP显著且剂量依赖性降低。钙通道阻滞剂导致的TTP降低通过添加钙完全逆转，且与心肌收缩力的恢复密切平行：在（Ca2+）1.34 mM时，维拉帕米10(-6)M使TTP从299±14毫秒显著降至250±11毫秒。在（Ca2+）15 mM时，TTP值分别为285±7毫秒（对照）和291±5毫秒（维拉帕米）。硝苯地平5×10(-7)M使TTP从343±20毫秒降至246±4毫秒（Ca 1.34 mM）。在钙浓度为15 mM时，TTP值分别为296±6毫秒（对照）和300±17毫秒（硝苯地平）。相反，在（Ca2+）1.34 mM时，异丙肾上腺素10(-5)M使TTP从266±14毫秒显著降至222±14毫秒，在（Ca2+）15 mM时仍存在这种降低：233±8毫秒（对照）和220±8毫秒（异丙肾上腺素）。结果表明，钙通道阻滞剂和异丙肾上腺素导致的TTP降低是由不同机制介导的。
