Cyclic AMP levels in rabbit carotid bodies incubated under control conditions, 100% O2- or 95% O2/5% CO2- equilibrated medium, are close to 1 pmol/mg wet tissue (range 0.4-2.43 pmol/mg). Isobutylmethylxanthine (0.5 mM) increases cyclic AMP levels by a factor of 14 and 8 in HEPES- and CO2/CH3O(-)-buffered medium, respectively. Forskolin (0.5-10 microM) applied during 30 min increases cyclic AMP levels in a dose-dependent manner. Incubation of carotid bodies at low O2 tensions resulted in an elevation of cyclic AMP levels both in the absence and in the presence of isobutymethylxanthine. In the latter conditions cyclic AMP increase was maximum at an O2 tension of 46 mm Hg and tended to decrease at extremely low PO2. In isobutylmethylxanthine-containing Ca2(+)-free medium, cyclic AMP increased linearly with decreasing PO2 from 66 to 13 mm Hg; the absolute cyclic AMP levels attained in Ca2(+)-free medium were smaller than those observed in Ca2(+)-containing medium at any PO2. The differences between Ca2(+)-free and Ca2(+)-containing media appear to be due to the action of released neurotransmitters in the latter conditions, because dopamine and norepinephrine, which are known to be released by hypoxia in a Ca2(+)-dependent manner, increase cyclic AMP in the carotid body. Low pH/high PCO2 and high [K+]e increase cyclic AMP levels only in Ca2(+)-containing medium. Forskolin potentiates the release of catecholamines induced by low PO2. These results suggest that cyclic AMP plays an important role in the modulation of the chemoreception process.

译文

在100% O2-或95% O2/5% CO2平衡的培养基的对照条件下孵育的兔颈动脉体中的循环AMP水平接近1 pmol/mg湿组织 (范围0.4-2.43 pmol/mg)。在HEPES-和CO2/CH3O(-) 缓冲介质中,异丁基甲基黄嘌呤 (0.5 mM) 使环状AMP水平分别增加14和8倍。在30分钟期间施加的福司可林 (0.5-10微米) 以剂量依赖性方式增加循环AMP水平。在低O2张力下孵育颈动脉体会在不存在和存在异丁甲基黄嘌呤的情况下导致环状AMP水平升高。在后一种条件下,循环AMP的增加在46毫米Hg的O2张力下最大,并在极低的po2下趋于降低。在含异丁基甲基黄嘌呤的无Ca2 () 的培养基中,环状AMP随着PO2从66 Hg降低到13毫米Hg而线性增加; 在无Ca2 () 的培养基中获得的绝对环状AMP水平小于在任何PO2下在含Ca2 () 的培养基中观察到的绝对环状AMP水平。不含Ca2(+) 和含Ca2(+) 的培养基之间的差异似乎是由于在后一种情况下释放的神经递质的作用,因为多巴胺和去甲肾上腺素,已知它们是由缺氧以Ca2(+) 依赖性方式释放的,增加颈动脉体中的循环AMP。低pH/高PCO2和高 [K] e仅在含Ca2 () 的培养基中增加循环AMP水平。Forskolin可增强低po2诱导的儿茶酚胺的释放。这些结果表明,循环AMP在化学感受过程的调制中起着重要作用。

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