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MIP has been hypothesized to be a gap junction protein, a membrane ion channel, a membrane water channel and a facilitator of glycerol transport and metabolism. These possible roles have been indirectly suggested by the localization of MIP in lens gap junctional plaques and the properties of MIP when reconstituted into artificial membranes or exogenously expressed in oocytes. We have examined lens fiber cells to see if these functions are present and whether they are affected by a mutation of MIP found in CatFr mouse lens. Of these five hypothesized functions, only one, the role of water channel, appears to be true of fiber cells in situ. Based on the rate of volume change of vesicles placed in a hypertonic solution, fiber cell membrane lipids have a low water permeability (pH2O) on the order of 1 micron/sec whereas normal fiber cell membrane pH2O was 17 micron/sec frog, 32 micron/sec rabbit and 43 micron/sec mouse. CatFr mouse lens fiber cell pH2O was reduced by 13 micron/sec for heterozygous and 30 micron/sec for homozygous mutants when compared to wild type. Lastly, when expressed in oocytes, the pH2O conferred by MIP is not sensitive to Hg2+ whereas that of CHIP28 (AQP1) is blocked by Hg2+. The fiber cell membrane pH2O was also not sensitive to Hg2+ whereas lens epithelial cell pH2O (136 micron/sec in rabbit) was blocked by Hg2+. With regard to the other hypothesized roles, fiber cell membrane or lipid vesicles had a glycerol permeability on the order of 1 nm/sec, an order of magnitude less than that conferred by MIP when expressed in oocytes. Impedance studies were employed to determine gap junctional coupling and fiber cell membrane conductance in wild-type and heterozygous CatFr mouse lenses. There was no detectable difference in either coupling or conductance between the wild-type and the mutant lenses.
K Varadaraj, and
C Kushmerick, and
G J Baldo, and
S Bassnett, and
A Shiels, and
R T Mathias
November 2003,
Journal of experimental zoology. Part A, Comparative experimental biology,
K Varadaraj, and
C Kushmerick, and
G J Baldo, and
S Bassnett, and
A Shiels, and
R T Mathias
February 1985,
Proceedings of the National Academy of Sciences of the United States of America,
K Varadaraj, and
C Kushmerick, and
G J Baldo, and
S Bassnett, and
A Shiels, and
R T Mathias
November 2009,
Molecular vision,
K Varadaraj, and
C Kushmerick, and
G J Baldo, and
S Bassnett, and
A Shiels, and
R T Mathias
November 1984,
Cell,
K Varadaraj, and
C Kushmerick, and
G J Baldo, and
S Bassnett, and
A Shiels, and
R T Mathias
September 2023,
Gene expression patterns : GEP,
K Varadaraj, and
C Kushmerick, and
G J Baldo, and
S Bassnett, and
A Shiels, and
R T Mathias
July 1999,
Journal of cell science,
K Varadaraj, and
C Kushmerick, and
G J Baldo, and
S Bassnett, and
A Shiels, and
R T Mathias
January 1982,
Biophysics of structure and mechanism,
K Varadaraj, and
C Kushmerick, and
G J Baldo, and
S Bassnett, and
A Shiels, and
R T Mathias
January 1991,
Molecular microbiology,
K Varadaraj, and
C Kushmerick, and
G J Baldo, and
S Bassnett, and
A Shiels, and
R T Mathias
November 1989,
The Journal of biological chemistry,
K Varadaraj, and
C Kushmerick, and
G J Baldo, and
S Bassnett, and
A Shiels, and
R T Mathias
March 1993,
Investigative ophthalmology & visual science,
