Serotonin-elicited inhibition of Cl(-) secretion in the rabbit conjunctival epithelium |
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Authors: | Alvarez L J Turner H C Zamudio A C Candia O A |
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Affiliation: | Department of Ophthalmology, Mount Sinai School of Medicine, New York, New York 10029, USA. larry.alvarez@mssm.edu |
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Abstract: | The effects of serotonin[5-hydroxytryptamine (5-HT)] on the transepithelial electricalproperties of the short-circuited rabbit conjunctiva were examined.With this epithelium, the short-circuit current(Isc) measures Cl secretion plusan amiloride-resistant Na+ absorptive process. Apicaladdition of 5-HT (10 µM) elicited a prompt Iscreduction from 14.2 ± 1.2 to 10.9 ± 1.2 µA/cm2 and increased transepithelial resistance from0.89 ± 0.05 to 1.03 ± 0.06 k · cm2(means ± SE, n = 21, P < 0.05).Similar changes were obtained with conjunctivae bathed withoutNa+ in the apical bath, as well as with conjunctivaepreexposed to bumetanide with the Cl-dependentIsc sustained by the parallel activities ofbasolateral Na+/H+ andCl/HCO exchangers. In contrast, the5-HT-evoked effects were attenuated by the absence of Cl(Isc = 0.5 ± 0.2, n = 5), suggesting that reduced Clconductance(s) is an effect of 5-HT exposure. In amphotericin B-treatedconjunctiva and in the presence of a transepithelial K+gradient, 5-HT addition reduced K+ diffusion across thepreparation by 13% and increased transepithelial resistance by 4%(n = 6, P < 0.05), indicating that aninhibition in K+ conductance(s) was also detectable.Significant electrical responses also occurred under physiologicalconditions when 5-HT was introduced to epithelia pretreated withadrenergic agonists or protein kinase C, phospholipase C,phosphodiesterase, or adenylyl cyclase inhibitors or after perturbationof Ca2+ homeostasis. Briefly, the conjunctiva harbors theonly known Cl-secreting epithelium in which 5-HT evokesCl transport inhibition; receptor subtype and signaltransduction mechanism were not determined. |
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