Beta-adrenergic inhibition of rabbit lens anterior-surface K(+) conductance.
OBJECTIVE
To characterize the effects of cAMP-elevating stimuli on the rabbit translens electrical parameters and examine the distribution of beta adrenoceptors about the epithelial surface.


METHODS
The electrophysiological experiments encompassed the isolation of lenses within a vertically arranged, Ussing-type chamber under short-circuit conditions, an approach that allowed for measurements of short-circuit current (I(sc)) across, in separate experiments, discrete surface regions. Epithelial beta receptors were localized by immunofluorescent labeling of lens cryosections primarily exposed to a polyclonal antibody against human beta( 2)-adrenoceptors. Reverse transcription - polymerase chain reaction (RT-PCR) was used to generate cDNA (using specific primers based upon the sequence of the previously cloned human beta(2) receptor) from rabbit lens RNA extracted from mechanically sequestered anterior and equatorial epithelial cells.


RESULTS
Asymmetrical I(sc) reductions with increases in translens resistance were elicited with epinephrine, isoproterenol, terbutaline, forskolin, and a lipid-permeable cAMP analogue. Electrical changes were recorded across the anterior aspect and not observed when the above compounds were applied to solutions bathing the equatorial and posterior surfaces. Immunohistochemical observations indicated the expression of beta receptors from the anterior epithelium to the equatorial region. RT-PCR yielded cDNA of expected basepair length for the apparent fragment of the beta(2)-adrenoceptor, which exhibited a sequence homology 90% identical with its human equivalent in both the anterior and equatorial epithelia.


CONCLUSIONS
The cAMP-sensitive conductance(s) appear limited to the anterior epithelium and undetectable equatorially. The asymmetrical I(sc) responses do not seem to arise from a spatial heterogeneity in epithelial receptor expression.
Alvarez
Lawrence J
LJ
Department of Ophthalmology, Mount Sinai School of Medicine, New York, NY 10029, USA. larry.alvarez@mssm.edu
Turner
Helen C
HC
Candia
Oscar A
OA
Polikoff
Lee A
LA
D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000818:Animals; D001692:Biological Transport; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D004553:Electric Conductivity; D004594:Electrophysiology; D004837:Epinephrine / Q000494:pharmacology; D004847:Epithelial Cells / Q000378:metabolism*; D019084:Fluorescent Antibody Technique, Indirect; D007545:Isoproterenol / Q000494:pharmacology; D007908:Lens, Crystalline / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism*; D015221:Potassium Channels / Q000187:drug effects*; D012333:RNA, Messenger / Q000378:metabolism; D011817:Rabbits; D018343:Receptors, Adrenergic, beta-2 / Q000235:genetics / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013726:Terbutaline / Q000494:pharmacology
D000318:Adrenergic beta-Agonists; D015221:Potassium Channels; D012333:RNA, Messenger; D018343:Receptors, Adrenergic, beta-2; D005576:Colforsin; D000242:Cyclic AMP; D007545:Isoproterenol; D013726:Terbutaline; D011188:Potassium; D004837:Epinephrine