Properties of chicken lens MIP channels reconstituted into planar lipid bilayers

E. Modesto, P. D. Lampe, M. C. Ribeiro, D. C. Spray, A. C. Campos De Carvalho

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Abstract

Membrane fractions highly enriched in chicken lens MLP (MIP28) were found to form ion channels when incorporated into planar lipid bilayers. The channels displayed prominent unitary conductances of about 60 and 290 pS in symmetric 150 mM KCl solution and were slightly anion selective. For both depolarizing and hyperpolarizing voltages, voltage sensitivity of the MIP28-induced conductance could be fit by a Boltzmann relation, symmetric around zero mV, with V0 = 18.5 mV, n = 4.5 and g(min)/g(max) = 0.17. Channel properties were not appreciably altered by pH in the range of 5.8 to 7, although channel incorporation was observed to occur more frequently at lower pH values. Calcium, at millimolar concentrations, decreased the channel mean open time. Partial proteolysis of MIP28 to yield MIP21 did not appreciably affect single-channel conductance or voltage sensitivity of the reconstituted channels. MIP28 was not phosphorylated by cAMP dependent protein kinase(PKA). Although unitary conductance and selectivity of the chicken MIP channel are similar to those reported for the bovine MIP (MIP26), the voltage sensitivity of MIP28 was higher than that of the bovine homologue, and voltage sensitivity of MIP28 was not modulated by treatments previously shown to affect MIP26 voltage gating (partial proteolysis and protein phosphorylation by PKA: (Ehring et al., 1990). The existence of such strikingly different functional properties in highly homologous channel isoforms may provide a useful system for exploration of the structure-function relations of MIP channels.

Original languageEnglish (US)
Pages (from-to)239-249
Number of pages11
JournalJournal of Membrane Biology
Volume154
Issue number3
DOIs
Publication statusPublished - Dec 1 1996

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Keywords

  • MIP
  • Phosphorylation
  • Proteolysis
  • Single channels
  • Voltage gating

ASJC Scopus subject areas

  • Biophysics
  • Physiology
  • Cell Biology

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