Charge pulse studies of transport phenomena in bilayer membranes. I. Steady-state measurements of actin- and valinomycin-mediated transport in glycerol monooleate bilayers

Abstract

A charge pulse technique has been applied to studies of transport phenomena in bilayer membranes. The membrane capacitance can be rapidly charged (in less than a microsecond). The charge then decays through the membrane's conductive mechanism-no current flows through the solution or external circuitry. The resulting voltage decay is thus a manifestation of membrane and boundary layer phenomena only. There are a number of advantages to this approach over conventional voltage or current-clamp techniques: the rise-time of the voltage perturbation is not limited by the time constant deriving from the membrane capacitance and solution resistance, thus permitting study of extremely rapid rate processes; the membrane is exposed to high voltage for relatively short times and thus can be subjected to higher voltages without breakdown; the steady-state current-voltage behavior of the membrane can be deduced from a single charge pulse experiment; the charge (and therefore the integral of the ion flux through the membrane) is monitored allowing detection of rate processes too rapid to follow directly. In this paper we present what is primarily a steady-state analysis of actin (non-, mon-, din-, trin-)-mediated transport of ammonium ion and valinomycin-mediated transport of cesium and potassium ions through glycerol monooleate bilayers. We introduce the concept of the "intercept discrepancy", a method for measuring charge lost through extremely rapid rate processes. Directly observable pre-steady-state phenomena are also discussed but will be the main subject of part II.