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Abstract #11336 Published in IGR 6-3
Inhibition of NHE-1 Na+/H+ exchanger by natriuretic peptides in ocular nonpigmented ciliary epithelium
Fidzinski P; Salvador Silva M; Choritz L; Geibel J; Coca Prados MAmerican Journal of Physiology and Cell Physiology 2004; 287: C655-663
The natriuretic peptides (NPs) atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), and C-type natriuretic peptide (CNP) display hypotensive effects in the mammalian eye by lowering the intraocular pressure (IOP), a function that is mediated by the bilayer ocular ciliary epithelium (CE), in conjunction with the trabecular meshwork. ANP regulates Na+/H+ exchanger (NHE) activity, and inhibitors of NHE have been shown to lower IOP. We examined whether NPs influence the NHE activity of the CE, which is comprised of pigmented (PE) and nonpigmented (NPE) epithelial cells, by directly recording the rate of intracellular pH (Phi) recovery from its inner NPE cell layer. NPs inhibited, in a dose-dependent manner (1-100 nM), the rate of Phi recovery with the order of potency CNP > ANP > BNP, indicative that this inhibition is mediated by the presence of NPR type B receptors. 8-Bromo-cGMP (8-BrcGMP), a nonhydrolyzable analog of cGMP, mimicked NPs in inhibiting the rate of Na+-dependent Phi recovery. In contrast, ethylisopropyl amiloride (EIPA, 100 nM) or amiloride (10 μM) completely abolished the Phi recovery by NHE. 18α-Glycyrrhetinic acid (18α-GA), a gap junction blocker, attenuated the inhibitory effect of CNP on the rate of Phi recovery, suggesting that NHE activity in both cell layers of the CE is coregulated. This interpretation was supported, in part, by the coexpression of NHE-1 isoform mRNA in both NPE and PE cells. The mechanism by which the inhibitory effect of NPs on NHE-1 activity might influence the net solute movement or fluid transport by the bilayer CE remains to be determined.
Dr. P. Fidzinski, Dept. of Ophthalmology and Visual Science, Yale University School of Medicine, New Haven, CT 06510, USA
Classification:
11.14 Investigational drugs; pharmacological experiments (Part of: 11 Medical treatment)
