Epinephrine-induced increases in [Ca2+](in) and KCl-coupled fluid absorption in bovine RPE.
OBJECTIVE
To define the ionic basis for the apical epinephrine-induced increase of fluid absorption (J(V)) across isolated bovine RPE-choroid.


METHODS
Epinephrine-induced changes in RPE [Ca2+](in) levels were monitored with the ratioing dye fura-2. Transepithelial potential, resistance, and unidirectional fluxes of (36)Cl, (86)Rb (K substitute), and (22)Na were simultaneously determined in paired tissues from the same eye mounted in modified Ussing flux chambers. Radioisotopes (5-7 microCi) were added to the apical bath of one tissue and the basal bath of the other, and the appearance of label in the opposite bath was measured.


RESULTS
Apical epinephrine (100 nM) transiently increased [Ca2+](in) by 153 +/- 78 nM. This increase was inhibited by the alpha(1)-adrenoreceptor antagonist prazosin (1 microM) and blocked by CPA(5 microM), an inhibitor of endoplasmic reticulum Ca2+-adenosine triphosphatases (ATPases). Apical epinephrine (100 nM) more than doubled the net Cl absorption rate, increased net K ((86)Rb) absorption by fivefold, and tripled net fluid absorption (J(V)), as predicted by isotonic coupling between ion and fluid transport. The epinephrine-induced increases in ion and fluid transport were completely inhibited by apical bumetanide (100 microM).


CONCLUSIONS
Epinephrine increased fluid absorption across bovine RPE by activating apical membrane alpha(1)-adrenergic receptors, increasing [Ca2+](in), and stimulating bumetanide-sensitive Na,K,2Cl uptake at the apical membrane and KCl efflux at the basolateral membrane.
Rymer
J
J
School of Optometry, University of California-Berkeley, Berkeley, CA 94720-2020, USA.
Miller
S S
SS
Edelman
J L
JL
D000042:Absorption; D000322:Adrenergic Agonists / Q000494:pharmacology*; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D001485:Basement Membrane / Q000378:metabolism; D001692:Biological Transport; D001826:Body Fluids / Q000378:metabolism*; D002034:Bumetanide / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D002352:Carrier Proteins / Q000378:metabolism; D002417:Cattle; D002829:Choroid / Q000187:drug effects / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004837:Epinephrine / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D016257:Fura-2 / Q000378:metabolism; D007552:Isotonic Solutions / Q000378:metabolism; D010857:Pigment Epithelium of Eye / Q000187:drug effects* / Q000378:metabolism; D011189:Potassium Chloride / Q000378:metabolism*; D011224:Prazosin / Q000494:pharmacology; D018340:Receptors, Adrenergic, alpha-1 / Q000378:metabolism; D000077331:Ringer's Solution; D028021:Sodium-Potassium-Chloride Symporters
D000322:Adrenergic Agonists; D000317:Adrenergic alpha-Antagonists; D002352:Carrier Proteins; D004791:Enzyme Inhibitors; D007552:Isotonic Solutions; D018340:Receptors, Adrenergic, alpha-1; D028021:Sodium-Potassium-Chloride Symporters; D002034:Bumetanide; D011189:Potassium Chloride; D000077331:Ringer's Solution; D000252:Calcium-Transporting ATPases; D002118:Calcium; D016257:Fura-2; D011224:Prazosin; D004837:Epinephrine