Abstract
The purpose of the present study was to investigate whether active Cl−secretion in the pigmented rabbit conjunctiva was subject to cAMP, Ca2+and protein kinase C (PKC) modulation. The excised pigmented rabbit conjunctivas were mounted in the modified Ussing-type chambers for measurement of unidirectional36Cl fluxes under the open-circuit condition and of the short-circuit current (Isc), potential difference, and transconjunctival electrical resistance. The results indicate that Cl−secretion across the conjunctiva was abolished by mucosal application of 1 mMN-phenylanthranilic acid and was reduced by 40% by serosal application of 10 μMbumetanide. Net Cl−flux was stimulated by 133% by 1 mM8-Br cAMP, 107% by 10 μMA23187, and 87% by 1 μMphorbol 12-myristate-13-acetate (PMA), suggesting that cAMP, Ca2+, and PKC all modulated active Cl−secretion, respectively. There existed a linear correlation between measured changes in net Cl−flux and observed changes in Isc(r2=0.99). The serial treatment of the conjunctiva with (a) 1 mM8-Br cAMP and 10 μMA23187 and (b) 10 μMA23187 and 1 μMPMA resulted in sequence-independent, additive stimulation of Isc. In the case of 1 mM8-Br cAMP and 1 μMPMA, additive stimulation of Iscwas observed only when 1 mM8-Br cAMP was added prior to 1 μMPMA. These results suggest that a given pharmacological agent may affect more than one channel type and that there might be a possible connection among the channels at the signal transduction level. In summary, Cl−appears to enter the pigmented rabbit conjunctiva from the serosal fluid via Na+-(K+)-2Cl−cotransport process and exit to the mucosal fluid via channels, resulting in active Cl−secretion. Active Cl−secretion in the pigmented rabbit conjunctiva appears to be modulated by cAMP, Ca2+, and PKC.
Published Version
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