Beta-adrenergic stimulation of Na+, K+, Cl- cotransport in fetal nonpigmented ciliary epithelial cells.
OBJECTIVE
The effects of adrenergic agonists and antagonists on Na+, K+, Cl- cotransport in fetal human nonpigmented ciliary epithelial (NPE) cells were investigated.


METHODS
86Rb+ as a marker for K+ was used to study ouabain-insensitive, bumetanide-sensitive 86Rb+ uptake in cultured NPE monolayers. Cyclic adenosine monophosphate (cAMP) formation in NPE cells was determined by radioimmunoassay.


RESULTS
1 microM isoproterenol caused a 1.65-fold stimulation in Na+,K+,Cl cotransport measured as bumetanide-sensitive, ouabain-insensitive 86Rb+ uptake. The half-maximal concentration for this effect was 6.4 nM, with maximal stimulation at 100 nM isoproterenol. Epinephrine stimulated Na+, K+, Cl- cotransport similarly to isoproterenol, whereas norepinephrine stimulated at much higher concentrations (half-maximal effective concentration = 1.4 microM). Stimulation of Na+, K+, Cl- cotransport by 1 microM isoproterenol was inhibited completely by the beta 2-adrenergic antagonist ICI-118,551 at 100 nM, with a half-maximal inhibitory concentration of 5 nM. Neither atenolol, a beta 1-specific adrenergic antagonist, prazosin, an alpha 1-adrenergic antagonist, nor yohimbine, an alpha 2-specific antagonist, was as effective. These four antagonists inhibited isoproterenol-stimulated cAMP formation with potencies similar to those observed against stimulated Na+, K+, Cl- cotransport. The hypotensive adrenergic antagonist timolol, propranolol, and betaxolol also inhibited Na+, K+, Cl- cotransport stimulated by isoproterenol in the order timolol > propranolol > betaxolol. Na+, K+, Cl- cotransport could be maintained in a stimulated state for at least 2 hours in the presence of agonist, but activity returned to basal levels within 20 minutes of isoproterenol removal. Adrenergic stimulation of Na+, K+, Cl- cotransport was blocked 80% to 85% by 70 microM H-89, a protein kinase A inhibitor.


CONCLUSIONS
These data suggest that beta 2-adrenergic receptor activation results in increased cAMP formation and sustained stimulation of Na+, K+, Cl- cotransport in fetal human NPE cells. Protein kinase A activation is required for maximal stimulation of Na+, K+, Cl- cotransport by adrenergic agonists.
Crook
R B
RB
Department of Opthalmology, University of California, San Francisco 94143, USA.
Riese
K
K
D018674:Adrenergic Antagonists / Q000494:pharmacology; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D001692:Biological Transport / Q000187:drug effects; D002478:Cells, Cultured; D002712:Chlorides / Q000378:metabolism*; D002924:Ciliary Body / Q000166:cytology / Q000187:drug effects / Q000196:embryology / Q000378:metabolism*; D000242:Cyclic AMP / Q000096:biosynthesis; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004848:Epithelium / Q000187:drug effects / Q000196:embryology / Q000378:metabolism; D005333:Fetus; D006801:Humans; D007473:Ion Channels / Q000037:antagonists & inhibitors; D010857:Pigment Epithelium of Eye / Q000187:drug effects / Q000196:embryology / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism*; D018343:Receptors, Adrenergic, beta-2 / Q000378:metabolism; D012413:Rubidium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*
D018674:Adrenergic Antagonists; D000316:Adrenergic alpha-Agonists; D000318:Adrenergic beta-Agonists; D002712:Chlorides; D007473:Ion Channels; D018343:Receptors, Adrenergic, beta-2; D012964:Sodium; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D012413:Rubidium; D011188:Potassium