Perry S F, Wood C M, Thomas S, Walsh P J
Department of Biology, University of Ottawa, Ontario, Canada.
J Exp Biol. 1991 May;157:367-80. doi: 10.1242/jeb.157.1.367.
We have used a sensitive new technique to assess the mechanism(s) of adrenergic inhibition of rainbow trout (Oncorhynchus mykiss) red blood cell (RBC) carbon dioxide excretion in vitro. The effect was only apparent using blood acidified to simulate metabolic acidosis. Red blood cell CO2 excretion was inhibited in a dose-dependent manner by physiologically relevant concentrations of noradrenaline (10-1000 nmol l-1) or adrenaline (100-1000 nmol l-1). The beta-adrenoceptor antagonist propranolol abolished the inhibitory effect of adrenaline, whereas the alpha-adrenoceptor antagonist phentolamine was without effect. The action of noradrenaline on RBC CO2 excretion was mimicked by the beta-adrenoceptor agonist isoproterenol, but not by the alpha-adrenoceptor agonist phenylephrine. Therefore, adrenergic inhibition of CO2 excretion is mediated by RBC beta-adrenoceptors, presumably of the beta 1 subtype. The Na+/H+ exchange inhibitor amiloride effectively blocked adrenergic stimulation of Na+/H+ exchange (as indicated from measurements of pHe and RBC pHi) and entirely prevented the inhibition of CO2 excretion. Noradrenaline significantly reduced the rate of CO2 excretion even in the presence of the Cl-/HCO3- exchange inhibitor SITS. Therefore, adrenergic inhibition of CO2 excretion is accomplished via activation of RBC Na+/H+ exchange rather than by a direct inhibition of Cl-/HCO3- exchange. The observed relationship between CO2 excretion rates and the RBC transmembrane pH difference (pHe-pHi) and the occurrence of the inhibition only at low pHe provide further evidence of the linkage with RBC Na+/H+ exchange. We suggest that adrenergic activation of RBC Na+/H+ exchange impedes CO2 excretion by causing a rise in intracellular HCO3- levels concurrent with a reduction of intracellular PCO2. The net result is a reduced gradient for HCO3- entry into the RBC in conjunction with a diminution of the outwardly directed PCO2 gradient. Thus, the rate of formation of CO2 from the dehydration of plasma HCO3- is reduced and, in turn, a portion of this CO2 is not excreted but recycled through the red blood cell.
我们采用了一种灵敏的新技术来评估肾上腺素能抑制虹鳟（Oncorhynchus mykiss）红细胞（RBC）体外二氧化碳排泄的机制。这种效应只有在使用酸化血液模拟代谢性酸中毒时才明显。生理相关浓度的去甲肾上腺素（10 - 1000 nmol l-1）或肾上腺素（100 - 1000 nmol l-1）以剂量依赖的方式抑制红细胞二氧化碳排泄。β-肾上腺素能受体拮抗剂普萘洛尔消除了肾上腺素的抑制作用，而α-肾上腺素能受体拮抗剂酚妥拉明则无作用。去甲肾上腺素对红细胞二氧化碳排泄的作用可被β-肾上腺素能受体激动剂异丙肾上腺素模拟，但不能被α-肾上腺素能受体激动剂去氧肾上腺素模拟。因此，肾上腺素能对二氧化碳排泄的抑制是由红细胞β-肾上腺素能受体介导的，推测为β1亚型。钠/氢交换抑制剂阿米洛利有效地阻断了肾上腺素能对钠/氢交换的刺激（从细胞外pH值和红细胞细胞内pH值的测量结果来看），并完全防止了二氧化碳排泄的抑制。即使在存在氯/碳酸氢根交换抑制剂SITS的情况下，去甲肾上腺素仍显著降低了二氧化碳排泄率。因此，肾上腺素能对二氧化碳排泄的抑制是通过激活红细胞钠/氢交换来实现的，而不是直接抑制氯/碳酸氢根交换。观察到的二氧化碳排泄率与红细胞跨膜pH差值（细胞外pH值 - 细胞内pH值）之间的关系以及仅在低细胞外pH值时出现抑制现象，进一步证明了与红细胞钠/氢交换的联系。我们认为，肾上腺素能激活红细胞钠/氢交换会阻碍二氧化碳排泄，原因是细胞内碳酸氢根水平升高，同时细胞内二氧化碳分压降低。最终结果是，碳酸氢根进入红细胞的梯度降低，同时外向的二氧化碳分压梯度减小。因此，血浆碳酸氢根脱水形成二氧化碳的速率降低，进而，一部分这种二氧化碳没有被排泄而是通过红细胞进行再循环。
