Fong J C
Biochim Biophys Acta. 1985 Apr 11;814(2):356-62. doi: 10.1016/0005-2736(85)90456-0.
The role of Ca2+ in the mediation of pepsinogen secretion from frog esophagus was investigated by means of ionophore A23187 and LaCl3. The esophageal mucosa from Asian bullfrog Rana tigerina was mounted in a double-chamber system to preserve its polarity and was incubated in a medium containing 1.5 mM CaCl2. Pepsinogen secreted was measured and expressed as % of total. The basal secretion averaged 3.5%/h. Bethanechol (25 microM), dibutyryl-cAMP (10 mM), ionophore A23187 (30 microM) and 3-isobutyl-1-methylxanthine (0.1 mM) increased the secretion to 8.7, 7.4, 7.1 and 6.8%, respectively. The stimulatory effect of bethanechol and of dibutyryl-cAMP were not affected by removing the exogenous Ca2+ with EGTA. The basal secretion was, however, reduced by 50% when Ca2+ in the incubation medium was lowered to 20 microM. At this low Ca2+ concentration, ionophore A23187 not only lost its stimulatory effect but also diminished the stimulation caused by bethanechol and dibutyryl-cAMP. While LaCl3 at 1 mM had no effect on basal and bethanechol-stimulated secretion, at 10 mM it abolished the stimulation evoked by bethanechol or dibutyryl-cAMP. The conclusions are: (1) both Ca2+ and cAMP are involved in the mediation of pepsinogen secretion from frog esophagus, (2) basal secretion is dependent on extracellular Ca2+, whereas bethanechol-stimulated secretion is not, (3) in the plasma membranes of peptic cells may exist a distinct Ca2+ pool (La3+-and ionophore A23187-sensitive) which is involved in the stimulated pepsinogen secretion.
采用离子载体A23187和LaCl3研究了Ca2+在介导青蛙食管胃蛋白酶原分泌中的作用。将亚洲牛蛙虎纹蛙的食管黏膜置于双室系统中以保持其极性，并在含有1.5 mM CaCl2的培养基中孵育。测定分泌的胃蛋白酶原并表示为总量的百分比。基础分泌平均为3.5%/小时。氨甲酰甲胆碱（25 μM）、二丁酰环磷腺苷（10 mM）、离子载体A23187（30 μM）和3-异丁基-1-甲基黄嘌呤（0.1 mM）分别将分泌增加至8.7%、7.4%、7.1%和6.8%。氨甲酰甲胆碱和二丁酰环磷腺苷的刺激作用不受用EGTA去除外源Ca2+的影响。然而，当孵育培养基中的Ca2+降至20 μM时，基础分泌减少了50%。在这种低Ca2+浓度下，离子载体A23187不仅失去了刺激作用，而且还减弱了氨甲酰甲胆碱和二丁酰环磷腺苷引起的刺激。虽然1 mM的LaCl3对基础分泌和氨甲酰甲胆碱刺激的分泌没有影响，但在10 mM时，它消除了氨甲酰甲胆碱或二丁酰环磷腺苷引起的刺激。结论是：（1）Ca2+和cAMP都参与介导青蛙食管胃蛋白酶原的分泌；（2）基础分泌依赖于细胞外Ca2+，而氨甲酰甲胆碱刺激的分泌则不依赖；（3）在胃细胞的质膜中可能存在一个独特的Ca2+池（对La3+和离子载体A23187敏感），它参与刺激胃蛋白酶原的分泌。
