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R. Wu, Y. Ni, I. Haefliger; Modulation by Calcium and Chloride of cAMP-Induced Short-Circuit Current Increase in Isolated Porcine Ciliary Processes. Invest. Ophthalmol. Vis. Sci. 2008;49(13):348.
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To investigate how calcium and chloride modulate short-circuit current (Isc) increase induced by 8-bromo-cAMP (cAMP) in isolated porcine ciliary processes.
In an Ussing-type chamber, peak Isc dose-response curves to the cAMP analogue 8-bromo-cAMP (0.01 µM - 30 µM) were constructed in isolated porcine ciliary processess. The effect of calcium channel blockers/stimulaters or calcium/chloride concentration in the bath solution on the Isc increase induced by cAMP analogue was assessed.
Only when applied on the non-pigmented epithelium side (NPE), 8-bromo-cAMP (0.01 - 30 µM) increased Isc (10 µM: 19.67 ± 2.44 µA/cm2). Isc increase was moderately inhibited by mibefradil (30 µM; P < 0.01), nimodipine (30 µM; P < 0.05), or a 0.5 mM calcium solution (P < 0.05), and almost abolished (P < 0.001) by a 0 mM calcium solution (with 2 mM EGTA) applied on the NPE. Isc increase was moderately enhanced by a 5 mM calcium solution (P < 0.01) or Bay K8644 (10 µM; P < 0.05) applied on the NPE. Isc increase was strongly inhibited by a 49.0 mM (P < 0.001) and 0 mM (P < 0.001) chloride solution applied on the pigmented epithelium side (PE). Inhibition by 0 mM chloride solution (PE) of Isc increase was not significantly affected by 0.5, 2.5, or 5 mM calcium solultion (NPE). Inhibition by 0 mM calcium (with 2 mM EGTA) solution (NPE) of Isc increase was not significantly affected by 0, 49.0, or 127.7 mM calcium solultion (PE).
cAMP-induced Isc increase appears to involve an extracellular influx of calcium on the NPE side and the presence of chloride on the PE side in pig ciliary processes. Furthermore, the absence of chloride and calcium on the PE and NPE side, respectively, appears to be limiting factors in this processes.
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