Ion, water and neutral solute transport in Xenopus oocytes expressing frog lens MIP

• Published in: Experimental eye research Vol. 61; no. 3; pp. 351 - 362
• Main Authors: Kushmerick, C., Rice, S.J., Baldo, G.J., Haspel, H.C., Mathias, R.T.
• Format: Journal Article
• Language: English
• Published: London Elsevier Ltd 01.09.1995; Elsevier
• Subjects: Animals; Aquaporins; Biological and medical sciences; Blotting, Western; Cell Membrane Permeability; Electrophoresis, Polyacrylamide Gel; Eye and associated structures. Visual pathways and centers. Vision; Eye Proteins - biosynthesis; Female; fiber cell; Fundamental and applied biological sciences. Psychology; Glycerol - pharmacokinetics; In Vitro Techniques; Ion Transport; lens MIP; Membrane Glycoproteins; neutral solute transport; Oocytes - metabolism; Rana pipiens; Time Factors; Vertebrates: nervous system and sense organs; Water - metabolism; water permeability; Xenopus; water permeability; fiber cell; neutral solute transport; Rana pipiens; ion transport; lens MIP; Eye; Visual system; Vertebrata; Frog; Intrinsic protein; Amphibia; Salientia; Lens; Ionic conductance; Gene expression; Water permeability
• ISSN: 0014-4835; 1096-0007
• DOI: 10.1016/S0014-4835(05)80129-0

We have expressed frog ( Rana pipiens) lens major intrinsic protein (MIP) in Xenopus oocytes and observed its effect on ion conductance, water permeability and neutral solute transport. SDS-PAGE and immunoblotting demonstrated oocytes injected with MIP mRNA expressed the protein at high levels. Immunolocalization indicated the expressed MIP migrated to the plasma membrane. MIP had no effect on the slope of oocyte I–V relations in the range − 50 to + 10 mV, although the averaged I–V curve was shifted 10 mV positive to control. MIP increased oocyte water permeability by a factor of 1·9 ± 0·2, whereas the permeability to sucrose, 2-deoxyglucose, inositol, sorbitol, reduced glutathione or urea was unchanged. Glycerol permeability was enhanced in oocytes expressing MIP. In contrast to control oocytes, 3H-glycerol radioactivity accumulation did not follow first order kinetics. Radioactivity continued to accumulate even after 19 h of uptake and went beyond equilibrium with the bath. The time course of MIP-mediated glycerol uptake was modeled assuming metabolic trapping with good results. Based on this model, MIP increased oocyte glycerol permeability by a factor of 2·7.