MIP 28 forms channels in planar lipid bilayers.
Fiber cells, which constitute most of the lens tissue, have large amounts of a protein named the main intrinsic protein (MIP) in their plasma membrane. MIP seems to vary among species. On SDS-PAGE, MIP from bovine lens (MIP 26) migrates faster than MIP from chicken lens (MIP 28), which runs as a 28-kDa protein. Recently a number of laboratories have shown that MIP 26 forms channels in lipid bilayers. We have isolated membrane fractions highly enriched in MIP 28 from chicken lens and incorporated channel activity into planar bilayers from these membrane fractions before and after treatment with the detergent Triton X-100. Detergent treatment does not seem to affect channel properties. We have attempted to block channel activity with polyclonal antibodies against bovine and chicken MIP but failed to detect blockade using either detergent-free or detergent-treated membranes. Single channel size in symmetric solutions of 300 mM K2SO4 (300-400 pS) agrees well with published results if one allows for corrections in ionic strength. Preliminary experiments indicate that the incorporated channels display voltage dependence. The channel activity recorded from MIP 28-enriched membrane fractions is qualitatively similar to that described for MIP 26 membrane fractions incorporated into bilayers. In contrast to previous reports, we do not find it necessary to add the membrane fractions to both sides of the bilayer to obtain channel incorporation. This may reflect the fact that MIP does not span two bilayers.
Modesto
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Instituto de Biofisica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Brasil.
Barcellos
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Campos-de-Carvalho
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D000818:Animals; D002645:Chickens; D005136:Eye Proteins / Q000502:physiology*; D007473:Ion Channels / Q000502:physiology*; D007908:Lens, Crystalline; D008565:Membrane Proteins / Q000502:physiology*; D017830:Octoxynol; D010713:Phosphatidylcholines; D010743:Phospholipids / Q000502:physiology; D011092:Polyethylene Glycols / Q000494:pharmacology*
D005136:Eye Proteins; D007473:Ion Channels; D008565:Membrane Proteins; D010713:Phosphatidylcholines; D010743:Phospholipids; C058303:lens intrinsic protein MIP 28; D011092:Polyethylene Glycols; C024990:asolectin; D017830:Octoxynol