Reinach P S
Curr Eye Res. 1985 Apr;4(4):385-91. doi: 10.3109/02713688509025152.
The messenger roles of cyclic AMP and the calcium ion in stimulus-secretion coupling are considered in the frog and bovine corneal epithelium, respectively. In the frog cornea, epinephrine stimulates net C1 transport by increasing cyclic AMP content. This stimulation is associated with a larger apical membrane C1 conductance and basolateral membrane ionic conductance. The response of the apical membrane conductance is thought to result from an increase in cyclic AMP content whereas the basolateral membrane ionic conductance increase is unrelated based on measurements of the effects of the calcium channel antagonist, diltiazem, and the beta agonist, isoproterenol, on the electrical parameters and cyclic AMP content. The basolateral membrane is essentially K permselective since the K channel blocker, Ba, depolarized the intracellular potential difference and increased the basolateral membrane resistance. Diltiazem had even larger effects on these parameters suggesting that this compound is a more effective inhibitor of K channel activity than barium. In broken cell preparations of bovine corneal epithelium, a high affinity form of Ca + Mg activated ATPase is present (Km = .06 microM for Ca) and is essentially of plasma membrane origin. This ATPase activation is at a Ca activity similar to the expected intracellular value and suggests that this activity is the enzymatic basis for net Ca transport.
分别在青蛙和牛角膜上皮中研究了环磷酸腺苷（cAMP）和钙离子在刺激-分泌偶联中的信使作用。在青蛙角膜中，肾上腺素通过增加cAMP含量来刺激净氯离子（Cl）转运。这种刺激与更大的顶端膜Cl电导和基底外侧膜离子电导有关。顶端膜电导的反应被认为是由于cAMP含量增加所致，而根据钙通道拮抗剂地尔硫䓬和β激动剂异丙肾上腺素对电参数和cAMP含量影响的测量结果，基底外侧膜离子电导的增加与之无关。由于钾通道阻滞剂钡使细胞内电位差去极化并增加了基底外侧膜电阻，因此基底外侧膜基本上对钾具有选择通透性。地尔硫䓬对这些参数的影响更大，表明该化合物比钡是更有效的钾通道活性抑制剂。在牛角膜上皮的破碎细胞制剂中，存在一种高亲和力形式的钙镁激活ATP酶（钙的米氏常数Km = 0.06微摩尔），且基本上起源于质膜。这种ATP酶的激活发生在与预期细胞内值相似的钙活性水平，表明这种活性是净钙转运的酶学基础。
