Nikinmaa M, Salama A, Bogdanova A, Virkki L V
Department of Biology, University of Turku, FIN-20014 Turku, Finland.
Physiol Biochem Zool. 2001 Jan-Feb;74(1):45-51. doi: 10.1086/319307.
We measured the effects of a beta-adrenergic agonist, isoproterenol, on chloride transport and volume regulation of lamprey (Lampetra fluviatilis) erythrocytes in isotonic (288 mosm L(-1)) and hypotonic (192 mosm L(-1)) medium. Isoproterenol at a high concentration (10(-5) M) did not influence chloride transport in isotonic medium but markedly increased chloride fluxes in hypotonic conditions: unidirectional flux increased from 100 mmol kg dcw(-1) h(-1) in the absence to 350 mmol kg dcw(-1) h(-1) (dcw=dry cell weight) in the presence of isoproterenol. Simultaneously, the half-time for volume recovery decreased from 27 to 9 min. Isoproterenol caused an increase in cellular cyclic AMP (cAMP) concentration. The stimulation of chloride transport in hypotonic conditions could be induced by application of the permeable cAMP analogue, 8-bromo-cyclic AMP, suggesting that the effect of beta-adrenergic stimulation on chloride transport occurs downstream of cAMP production. As isoproterenol did not affect unidirectional rubidium fluxes in hypotonic conditions, the transport pathway influenced by beta-adrenergic stimulation is most likely the swelling-activated chloride channel. Because the beta-adrenergic agonist only influenced the transport in hypotonic conditions despite the fact that cAMP concentration also increased in isotonic conditions, the activation may involve a volume-dependent conformational change in the chloride channel.
我们测定了β-肾上腺素能激动剂异丙肾上腺素对七鳃鳗（Lampetra fluviatilis）红细胞在等渗（288 mosm L⁻¹）和低渗（192 mosm L⁻¹）介质中氯离子转运和体积调节的影响。高浓度（10⁻⁵ M）的异丙肾上腺素在等渗介质中不影响氯离子转运，但在低渗条件下显著增加氯离子通量：单向通量在无异丙肾上腺素时为100 mmol kg dcw⁻¹ h⁻¹，在有异丙肾上腺素时增加到350 mmol kg dcw⁻¹ h⁻¹（dcw = 干细胞重量）。同时，体积恢复的半衰期从27分钟降至9分钟。异丙肾上腺素导致细胞内环磷酸腺苷（cAMP）浓度升高。在低渗条件下对氯离子转运的刺激可通过应用可渗透的cAMP类似物8-溴环磷酸腺苷来诱导，这表明β-肾上腺素能刺激对氯离子转运的作用发生在cAMP产生的下游。由于异丙肾上腺素在低渗条件下不影响单向铷通量，受β-肾上腺素能刺激影响的转运途径很可能是肿胀激活的氯离子通道。因为尽管在等渗条件下cAMP浓度也升高，但β-肾上腺素能激动剂仅在低渗条件下影响转运，所以激活可能涉及氯离子通道中依赖于体积的构象变化。
