Changes in the volume of marginal cells induced by isotonic ‘Cl− depletion/restoration’: involvement of the Cl− channel and Na+-K+-Cl− cotransporter

• Published in: Hearing research 1997-11, Vol.113 (1-2), p.99-109
• Main Authors: Takeuchi, Shunji, Ando, Motonori, Irimajiri, Akihiko
• Format: Article
• Language: English
• Subjects: Animals; Bumetanide - pharmacology; Carrier Proteins - metabolism; Cell Size - drug effects; Cell Size - physiology; Cell volume; Chloride Channels - antagonists & inhibitors; Chloride Channels - metabolism; Chlorides - metabolism; Cl− channel; Epithelial Cells - cytology; Epithelial Cells - drug effects; Epithelial Cells - metabolism; Gerbil; Gerbillinae; In Vitro Techniques; Inner ear; Intracellular Fluid - metabolism; Ion Transport - drug effects; Isotonic Solutions; Na+-K+-Cl− cotransporter; Nitrobenzoates - pharmacology; Ouabain - pharmacology; Potassium - metabolism; Sodium - metabolism; Sodium-Potassium-Chloride Symporters; Stria Vascularis - cytology; Stria Vascularis - drug effects; Stria Vascularis - metabolism
• ISSN: 0378-5955; 1878-5891
• DOI: 10.1016/S0378-5955(97)00134-2

Marginal cells constitute the endolymph-facing epithelium responsible for the secretion of endolymph by the stria vascularis in the inner ear. We have studied the possible involvement of Cl− conductance and Na+-K+-Cl− cotransport in the mechanism of changes in cell volume upon isotonic Cl− depletion/restoration. Changes in cell volume were estimated from video-microscopic images with the aid of an image processor. Marginal cells shrank to ∼80% of their original volume in 30 s and to 65–70% in 90 s upon total replacement of [Cl]o (∼150 mM) by gluconate−, and the original volume of the shrunken cells was restored within 2 min after restoration of Cl−. The order of potency of anions to induce isotonic shrinkage was gluconate−>I−>F−>Br−. The cell shrinkage caused by Cl− depletion was partially inhibited by 5-Nitro-2-(3-phenyl-propylamino)-benzoic acid (NPPB, 0.2 mM), but not by either 4-acetamido-4′-isothiocyanato-stilbene-2,2′-disulfonic acid (SITS, 0.5 mM), bumetanide (10 μM) or ouabain (1 mM). The cell shrinkage caused by a reduction of [Cl]o from ∼150 mM to 7.5 mM was not affected by [K]o in the range of 3.6 mM to 72 mM. These results suggest that the main efflux pathway(s) responsible for the ‘Cl removal’-induced shrinkage depends on volume-correlated Cl− conductance (Takeuchi and Irimajiri, J. Membrane Biol. 150, 47–62, 1996) and that this pathway(s) is essentially independent of the Na+-K+-Cl− cotransporter, the Na+,K+-ATPase, and the K+-Cl− cotransporter. With regard to volume recovery after isotonic shrinkage, its critical dependence on the simultaneous presence of Na+, K+ and Cl− in the bath and its substantial inhibition by bumetanide (10 μM) both indicate a major role for Na+-K+-Cl− cotransport. The strong influence on cell volume of solute fluxes working through the Cl− channel and the Na+-K+-Cl− cotransporter implies an essential role for these pathways in the ion transport mechanism(s) of the marginal cell.