Beta-adrenergic stimulation of volume-sensitive chloride transport in lamprey erythrocytes.
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.
Department of Biology, University of Turku, FIN-20014 Turku, Finland. miknik@utu.fi
M
M
Nikinmaa
A
A
Salama
A
A
Bogdanova
L V
LV
Virkki
D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000818:Animals; D018118:Chloride Channels / Q000502:physiology*; D002712:Chlorides / Q000493:pharmacokinetics; D000242:Cyclic AMP / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004912:Erythrocytes / Q000502:physiology; D007545:Isoproterenol / Q000494:pharmacology*; D007798:Lampreys / Q000502:physiology*; D014882:Water-Electrolyte Balance / Q000502:physiology*
D000318:Adrenergic beta-Agonists; D018118:Chloride Channels; D002712:Chlorides; D000242:Cyclic AMP; D007545:Isoproterenol