CORRELATIONS BETWEEN CHANGES IN MEMBRANE CAPACITANCE INDUCED BY CHANGES IN IONIC ENVIRONMENT AND THE CONDUCTANCE OF CHANNELS INCORPORATED INTO BILAYER-LIPID MEMBRANES

The action of metal polycations and pH on ionic channels produced in b ilayer lipid membranes (BLM) by three different toxins was studied by measuring membrane capacitance and channel conductance. Here, we show that critical concentrations of Cd2+, La3+ or Tb3+ induce complex chan ges in membrane capacitance. The time course of capacitance changes is similar to the time course of channel blocking by these ions at low c oncentration. No changes in BLM capacitance or conductance were observ ed in the range of pH 5.8-9.0. A pH shift from 7.4 to 3-4 or 11-12 ind uced large changes in BLM capacitance and channel conductance. For all studied channel-forming proteins, the initial capacitance increase pr eceded the conductance decrease caused by addition of polycations or b y a change in pH. A close relationship between membrane lipid packing and ion channel protein is suggested.