Modeling the current-voltage characteristics of charophyte membranes. III. K+ state of Lamprothamnium

Abstract

The K + state of salt-tolerant charophyte Lamprothamnium papulosum (Wallr.) J. Gr., acclimated to 0.5 seawater (SW) containing 4.5 mM K + , was investigated by exposing the cells to a range of [K + ] _o from 0 to 45.0 mM . The current–voltage (I/V) characteristics were modeled as a sum of four different transporter currents: the large conductance K + channel current, inward and outward K + rectifier currents and linear background current. The first three transporters were fitted with the Goldmann-Hodgkin-Katz (GHK) model. The potential difference (PD) dependence of the population of open channels was simulated by Boltzmann probability distribution. The linear background current exhibited reversal PD independent of lsqb;K + ] _o and the background conductance decreased as lsqb;K + ] _o increased. The combined channel number and permeability parameter, N _K P _K , was in a similar range for all three K + transporters. The N _K P _K parameter of the large conductance K + channel reached a maximum at lsqb;K + ] _o concentration of 9 mM , decreasing at 45 mM . The modeled large conductance K + channel revealed a strong asymmetry of the I/V profile in response to change of outside and inside K + concentrations. This behaviour was exploited to estimate the rise of cytoplasmic K + concentration at the time of the hypotonic effect. The cytoplasmic K + concentration range giving the best fit to the data in steady-state was 28–65 mM .