Inoue M, Fong J, Shah G, Hirschowitz B I
Am J Physiol. 1985 Jan;248(1 Pt 1):G79-86. doi: 10.1152/ajpgi.1985.248.1.G79.
The in vitro release of pepsinogen secretion by the isolated esophagus of the American bullfrog was studied with an improved model system. The tissue was mounted in a double chamber that preserves mucosal polarity and provides both control and test segments, each 1 cm2 from the same tissue. Pepsinogen secretion was severalfold higher than previously found with mucosal strips and could be sustained for several hours. Bethanechol (BCh) caused concentration-dependent (0.1-50 microM) pepsinogen secretion with a Vmax of 74 +/- 12 micrograms X mg prot-1 X h-1 or 50-60% of total pepsinogen; Km was 3 microM and 500 microM BCh stimulated at less than the Vmax value. Atropine specifically blocked BCh and pA2 = 9.3. In the presence of 100 microM isobutylmethyxanthine, BCh produced a dose-dependent increase in tissue cAMP but not cGMP. BCh remained effective in Ca2+-free medium. In calcium-free medium EGTA concentration dependently (0.2-5 mM) suppressed the pepsinogen response to BCh. The evidence thus far suggests that cholinergic stimulation of pepsinogen secretion in the tissue acts via both cAMP and Ca2+. More specific studies would be required for absolute confirmation of either or both apparent mechanisms and to resolve how they interact.
利用改进的模型系统研究了美国牛蛙离体食管胃蛋白酶原分泌的体外释放情况。将组织安装在一个双腔室中，该双腔室可保持黏膜极性，并提供对照段和测试段，每段均来自同一组织，面积为1平方厘米。胃蛋白酶原的分泌比之前用黏膜条测得的结果高出数倍，且可持续数小时。氨甲酰甲胆碱（BCh）引起胃蛋白酶原分泌呈浓度依赖性（0.1 - 50微摩尔），Vmax为74 ± 12微克×毫克蛋白⁻¹×小时⁻¹，占总胃蛋白酶原的50 - 60%；Km为3微摩尔，500微摩尔BCh的刺激作用小于Vmax值。阿托品特异性阻断BCh，pA2 = 9.3。在存在100微摩尔异丁基甲基黄嘌呤的情况下，BCh使组织中的cAMP呈剂量依赖性增加，但不影响cGMP。BCh在无钙培养基中仍然有效。在无钙培养基中，乙二醇双（2-氨基乙基醚）四乙酸（EGTA）浓度依赖性（0.2 - 5毫摩尔）抑制胃蛋白酶原对BCh的反应。目前的证据表明，组织中胆碱能刺激胃蛋白酶原分泌是通过cAMP和Ca²⁺共同起作用的。需要进行更具体的研究来绝对确认这两种明显机制中的一种或两种，并解决它们如何相互作用的问题。
