beta-Adrenergic stimulation of volume-sensitive chloride transport in lamprey erythrocytes

We measured the effects of a beta -adrenergic agonist, isoproterenol, on ch loride transport and volume regulation of lamprey (Lampetra fluviatilis) er ythrocytes 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 hyp otonic 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 re covery decreased from 27 to 9 min. Isoproterenol caused an increase in cell ular cyclic AMP (cAMP) concentration. The stimulation of chloride transport in hypotonic conditions could be induced by application of the permeable c AMP analogue, 8-bromo-cyclicAMP, suggesting that the effect of beta -adrene rgic stimulation on chloride transport occurs downstream of cAMP production . As isoproterenol did not affect unidirectional rubidium fluxes in hypoton ic conditions, the transport pathway influenced by beta -adrenergic stimula tion is most likely the swelling-activated chloride channel. Because the be ta -adrenergic agonist only influenced the transport in hypotonic condition s despite the fact that cAMP concentration also increased in isotonic condi tions, the activation may involve a volume-dependent conformational change in the chloride channel.