title: A Ca2+-activated channel from Xenopus laevis oocyte membranes reconstituted into planar bilayers.
abstract: Plasma membrane fractions from Xenopus laevis oocytes were incorporated into planar lipid bilayers. We show the existence of numerous Ca2+-activated nonspecific channels that are more permeable to anions. These channels are activated by Ca2+ at micromolar concentration but not by Mg2+, Zn2+, or Mn2+, even at millimolar concentrations. Decreasing Ca2+ concentration to less than 1 microM decreases the time of channel opening until channels close completely in the absence of Ca2+ and in the presence of EGTA. I- and Br- are more permeable through this channel than Cl-. The time during which the channels remain open is also voltage-dependent, with the channels switching off at higher voltages in both polarities. Single-channel activity shows a conductance of 380 pS in 1 M NaCl and 1 mM CaCl2, with an average open lifetime of 1.5 s at 40 mV. Similar channels are found in different stages of oocyte maturation. These observations support the hypothesis that an increase in oocyte-free Ca2+ activates directly these channels, and the resultant Cl- efflux forms the ionic basis for the fertilization potential in X. laevis.
mesh_terms: D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002413:Cations, Divalent; D002462:Cell Membrane / Q000502:physiology; D005260:Female; D007473:Ion Channels / Q000187:drug effects / Q000502:physiology*; D007700:Kinetics; D008051:Lipid Bilayers; D008565:Membrane Proteins / Q000502:physiology; D009865:Oocytes / Q000502:physiology*; D014981:Xenopus
chemical_list: D002413:Cations, Divalent; D007473:Ion Channels; D008051:Lipid Bilayers; D008565:Membrane Proteins; D002118:Calcium