Henry R P, Wang Y, Wood C M
Department of Zoology, Auburn University, Alabama 36849-5414, USA.
Am J Physiol. 1997 Jun;272(6 Pt 2):R1754-61. doi: 10.1152/ajpregu.1997.272.6.R1754.
An isolated, perfused tail preparation was used to study the role of carbonic anhydrase (CA) in CO2 and NH3 transport across the sarcolemma of white muscle in the rainbow trout. Tissue was perfused with either control saline or saline containing the CA inhibitors quaternary ammonium sulfanilamide (QAS) or acetazolamide (Az). Inhibition of extracellular CA by QAS reduced CO2 efflux by approximately 30% and caused a significant increase in intracellular PCO2. Inhibition of total muscle CA activity (extracellular and intracellular) by Az also caused a reduction in CO2 efflux, but selective inhibition of intracellular CA only had no effect. Inhibition of both extracellular and intracellular CA activity resulted in increases in total intracellular ammonia concentrations, intracellular NH3 partial pressure (PNH3) and an increased PNH3 gradient across the sarcolemma. This suggests that both extracellular and intracellular CA function in normal NH3 transport out of the muscle. We suggest that CA in the extracellular boundary layer facilitates CO2 transport via the catalyzed hydration of CO2, thus maintaining the PCO2 gradient across the sarcolemma. H ions produced by that reaction serve to protonate excreted NH3, which helps maintain the PNH3 gradient. Thus CO2 and NH3 excretion are linked by the action of CA.
采用离体灌注鱼尾制备方法，研究碳酸酐酶（CA）在虹鳟白肌肌膜跨膜转运二氧化碳和氨过程中的作用。用对照生理盐水或含CA抑制剂季铵磺胺（QAS）或乙酰唑胺（Az）的生理盐水灌注组织。QAS抑制细胞外CA可使二氧化碳外流减少约30%，并导致细胞内PCO2显著升高。Az抑制总肌肉CA活性（细胞外和细胞内）也会导致二氧化碳外流减少，但仅选择性抑制细胞内CA则无影响。抑制细胞外和细胞内CA活性均导致细胞内总氨浓度、细胞内NH3分压（PNH3）升高，以及跨肌膜的PNH3梯度增大。这表明细胞外和细胞内CA在正常情况下均参与肌肉中氨的转运。我们认为，细胞外边界层中的CA通过催化二氧化碳水合作用促进二氧化碳转运，从而维持跨肌膜的PCO2梯度。该反应产生的H离子使排泄出的NH3质子化，这有助于维持PNH3梯度。因此，CA的作用将二氧化碳和氨的排泄联系起来。
