Downes H, Edelstein R A, Taylor S M
Br J Pharmacol. 1986 Mar;87(3):579-86. doi: 10.1111/j.1476-5381.1986.tb10200.x.
Bullfrog hemilungs showed minimal relaxation (9 +/- 2% of the maximal relaxant effect of theophylline, Imax) after a 16 h incubation in 10(-5) M indomethacin, indicating that prostaglandin synthesis plays little or no role in the high intrinsic tone characteristic of this preparation. A higher concentration of indomethacin (10(-4) M) produced greater relaxation (23 +/- 3% of Imax), but also markedly potentiated isoprenaline-induced relaxation. The interaction with isoprenaline was similar to that previously found for papaverine, a phosphodiesterase inhibitor. Ouabain (10(-5) and 10(-4) M) produced an initial contraction followed by marked relaxation (50% of Imax), indicating that a ouabain-sensitive mechanism is of major importance in the maintenance of intrinsic tone. Ouabain-treated hemilungs showed reversal (relaxation) of the normal contractile response to 26 mM potassium and marked impairment of the contractile response to calcium in calcium-depleted preparations. These effects suggest that ouabain-induced relaxation reflects a drug action on calcium movements. The marked relaxation (30 to 40% of Imax) produced by 26 mM potassium in ouabain-treated hemilungs is of particular interest in that it indicates a mechanism of potassium-induced relaxation distinct from stimulation of sodium-potassium ATPase.
牛蛙半肺在10⁻⁵ M吲哚美辛中孵育16小时后，显示出最小程度的舒张（为茶碱最大舒张效应Imax的9±2%），这表明前列腺素合成在该制剂的高内在张力特性中作用很小或不起作用。更高浓度的吲哚美辛（10⁻⁴ M）产生了更大程度的舒张（为Imax的23±3%），但也显著增强了异丙肾上腺素诱导的舒张。与异丙肾上腺素的相互作用类似于先前发现的磷酸二酯酶抑制剂罂粟碱的情况。哇巴因（10⁻⁵和10⁻⁴ M）产生了最初的收缩，随后是显著的舒张（为Imax的50%），这表明哇巴因敏感机制在维持内在张力中起主要作用。用哇巴因处理的半肺对26 mM钾的正常收缩反应出现逆转（舒张），并且在缺钙制剂中对钙的收缩反应明显受损。这些效应表明，哇巴因诱导的舒张反映了药物对钙运动的作用。在经哇巴因处理的半肺中，26 mM钾产生的显著舒张（为Imax的30%至40%）特别令人感兴趣，因为这表明钾诱导舒张的机制不同于对钠钾ATP酶的刺激。
