Manganel M, Turner R J
Clinical Investigations and Patient Care Branch, National Institute of Dental Research, National Institutes of Health, Bethesda, Maryland 20892.
J Biol Chem. 1991 Jun 5;266(16):10182-8.
We demonstrate a rapid activation of the Na+/H+ exchanger in intact rat parotid acini in response to muscarinic (carbachol; K1/2 = 0.4 microM) and alpha-adrenergic (epinephrine; K1/2 = 0.1 microM) stimulation. This rapid activation is apparently distinct from the relatively "slow" activation of the exchanger (t1/2 greater than or equal to 5 min) reported previously (Manganel, M., and Turner, R. J. (1989) J. Membr. Biol. 111, 191-198). This rapid activation is not produced by treatment of acini with active diacylglycerol analogues nor prevented by protein kinase inhibitors, arguing against the involvement of protein kinase C-dependent processes. Stimulation of the exchanger is, however, produced by concentrations of ionomycin which yield intracellular calcium levels in the physiologic (secretagogue-induced) range. In addition, chelation of intracellular calcium with 1,2-bis(O-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid blocks the effect of carbachol, but calmodulin antagonists are without effect. The possibility that the rapid activation of the Na+/H+ exchanger may be associated with cell shrinkage arising from carbachol-induced calcium mobilization is explored. In support of this suggestion we present evidence that: (i) the Na+/H+ exchanger is stimulated by shrinkage of these cells, (ii) the carbachol dose dependence of Na+/H+ exchange activation correlates well with that of shrinkage (but not with that of intracellular calcium levels), and (iii) maneuvers which blunt carbachol- or calcium-induced shrinkage also blunt activation of the exchanger. We suggest that this osmoregulatory response may play an important role in maintaining ionic homeostasis during the acinar fluid secretory process.
我们证明，在完整的大鼠腮腺腺泡中，毒蕈碱（卡巴胆碱；半最大效应浓度(K_{1/2}=0.4)微摩尔）和α-肾上腺素能（肾上腺素；(K_{1/2}=0.1)微摩尔）刺激可快速激活钠氢交换体。这种快速激活明显不同于先前报道的交换体相对“缓慢”的激活（半衰期(t_{1/2}\geq5)分钟）（曼加内尔，M.，和特纳，R. J.（1989年）《膜生物学杂志》111卷，191 - 198页）。这种快速激活不是由用活性二酰甘油类似物处理腺泡产生的，也不能被蛋白激酶抑制剂阻止，这表明蛋白激酶C依赖性过程未参与其中。然而，离子霉素浓度产生生理（促分泌剂诱导）范围内的细胞内钙水平时，可刺激交换体。此外，用1,2 - 双（O - 氨基苯氧基）乙烷 - N,N,N',N' - 四乙酸螯合细胞内钙可阻断卡巴胆碱的作用，但钙调蛋白拮抗剂无效。我们探讨了钠氢交换体的快速激活可能与卡巴胆碱诱导的钙动员引起的细胞收缩相关的可能性。支持这一观点的证据如下：（i）这些细胞的收缩可刺激钠氢交换体；（ii）钠氢交换激活的卡巴胆碱剂量依赖性与收缩的剂量依赖性密切相关（但与细胞内钙水平的剂量依赖性无关）；（iii）减弱卡巴胆碱或钙诱导的收缩的操作也会减弱交换体的激活。我们认为这种渗透调节反应可能在腺泡液体分泌过程中维持离子稳态方面发挥重要作用。
