Capovilla M, Cervetto L, Torre V
Proc Natl Acad Sci U S A. 1982 Nov;79(21):6698-702. doi: 10.1073/pnas.79.21.6698.
Treatment of toad rods with phosphodiesterase inhibitors (3-isobutyl-1-methylxanthine, caffeine, theophylline, papaverine, and RO 20-1724) modifies the properties of the intracellular voltage responses to dim flashes of light. 3-Isobutyl-1-methylxanthine at 1-20 microM causes an increase in flash sensitivity and a slowing down of the kinetics of the photoresponses. When the drug concentration is greater than 20 microM, rods also show supralinear behavior, whereby doubling the intensity of a dim flash may increase the response by greater than 2-fold. Sensitivity, kinetics, and supralinear behavior can be restored to normal by steady background illumination while still in the presence of 3-isobutyl-1-methylxanthine. However, the intensity of the steady light needed to restore the sensitivity to control levels is not sufficient to accelerate the kinetics back to control values. The antagonism between the effects of 3-isobutyl-1-methylxanthine and the effects of background illumination is explained by assuming that: (i) the length of time to peak voltage responses to dim flashes of light is inversely proportional to the rate of a chemical reaction; (ii) the rate of this reaction is controlled by an enzyme that is inhibited competitively by 3-isobutyl-1-methylxanthine with a Ki of 3 x 10(-6) M; and (iii) the concentration of a cofactor of this reaction increases proportionally with the intensity of the background illumination.
用磷酸二酯酶抑制剂（3 - 异丁基 - 1 - 甲基黄嘌呤、咖啡因、茶碱、罂粟碱和RO 20 - 1724）处理蟾蜍视杆细胞，可改变细胞对弱闪光的电压反应特性。1 - 20微摩尔的3 - 异丁基 - 1 - 甲基黄嘌呤会使闪光敏感度增加，光反应动力学减慢。当药物浓度大于20微摩尔时，视杆细胞还会表现出超线性行为，即弱闪光强度加倍可能会使反应增加超过2倍。在仍存在3 - 异丁基 - 1 - 甲基黄嘌呤的情况下，通过稳定的背景光照可使敏感度、动力学和超线性行为恢复正常。然而，将敏感度恢复到对照水平所需的稳定光强度不足以使动力学加速回到对照值。3 - 异丁基 - 1 - 甲基黄嘌呤的作用与背景光照的作用之间的拮抗作用可通过以下假设来解释：（i）对视杆细胞对弱闪光的电压反应达到峰值所需的时间与化学反应速率成反比；（ii）该反应的速率由一种酶控制，3 - 异丁基 - 1 - 甲基黄嘌呤以3×10⁻⁶ M的抑制常数对其进行竞争性抑制；（iii）该反应的一种辅因子的浓度与背景光照强度成比例增加。
