Abscisic acid stimulation of ion transport and alteration in K+/Na+ selectivity

Lens ion homeostasis is crucial in maintaining water content and, in turn, refractive index and transparency of the multicellular syncytium-like structure. New information is emerging on the regulation of ion transport in the lens by mechanisms that rely on transient receptor potential vanilloid (TRPV) ion channels. We found recently that TRPV1 activation leads to Ca2+/PKC-dependent ERK1/2 signaling. Here, we show that the TRPV1 agonist capsaicin (100 nM) and hyperosmotic solution (350 vs. 300 mosM) each caused an increase of bumetanide-inhibitable Rb uptake by intact porcine lenses and Na-K-2Cl cotransporter 1 (NKCC1) phosphorylation in the lens epithelium. The TRPV1 antagonist A889425 (1 µM) abolished the increases of Rb uptake and NKCC1 phosphorylation in response to hyperosmotic solution. Exposing lenses to hyperosmotic solution in the presence of MEK/ERK inhibitor U0126 (10 µM) or the with-no-lysine kinase (WNK) inhibitor WNK463 (1 µM) also prevented NKCC1 phosphorylation and the Rb uptake responses to hyperosmotic solution. WNK463 did not prevent the increase in ERK1/2 phosphorylation that occurs in response to capsaicin or hyperosmotic solution, suggesting that ERK1/2 activation occurs before WNK activation in the sequence of signaling events. Taken together, the evidence indicates that activation of TRPV1 is a critical early step in a signaling mechanism that responds to a hyperosmotic stimulus, possibly lens shrinkage. By activating ERK1/2 and WNK, TRPV1 activation leads to NKCC1 phosphorylation and stimulation of NKCC1-mediated ion transport.

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Vasoactive intestinal peptide stimulates protein phosphorylation in a colonic epithelial cell line

AJP Gastrointestinal and Liver Physiology ◽

10.1152/ajpgi.1987.253.3.g420 ◽

1987 ◽

Vol 253 (3) ◽

pp. G420-G424 ◽

Cited By ~ 4

Author(s):

J. A. Cohn

Keyword(s):

Epithelial Cell ◽

Ion Transport ◽

Protein Phosphorylation ◽

Cell Line ◽

Vasoactive Intestinal Peptide ◽

Epithelial Cell Line ◽

Colonic Epithelial Cell ◽

Ussing Chambers ◽

Colonic Epithelial Cell Line ◽

Stimulation Of

The T84 colonic epithelial cell line was used to examine protein phosphorylation during neurohumoral stimulation of ion transport. T84 cell monolayers grown on collagen-coated filters were mounted in Ussing chambers to measure ion transport stimulated by vasoactive intestinal peptide. Maximal stimulation of active secretion occurred after 8-10 min of stimulation. Protein phosphorylation events accompanying stimulated secretion were detected using two-dimensional gel electrophoresis to resolve phosphoproteins from monolayers previously labeled using 32Pi. Within 8 min of exposure to vasoactive intestinal peptide, several phosphorylation events were detected, including a two- to fivefold increase in 32P incorporation into four soluble proteins with apparent molecular weights of 17,000, 18,000, 23,000, and 37,000. The same phosphorylation response occurs in monolayers stimulated by dibutyryl adenosine 3',5'-cyclic monophosphate (cAMP), suggesting that cAMP mediates these intracellular events. This study indicates that changes in protein phosphorylation accompany the secretory action of vasoactive intestinal peptide and suggests that T84 cells offer a useful model for studying the possibility that such phosphorylation events regulate enterocyte ion transport.

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