Summary

The K⁺ state of salt-tolerant charophyte Lamprothamnium papulosum, 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 GHK (Goldmann, Hodgkin and Katz) 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 [K⁺]_o and the background conductance decreased as [K⁺]_o increased. The combined channel number and permeability parameter, N_KP_K, was in a similar range for all the three K⁺ transporters. The N_KP_K parameter of the large conductance K⁺ channel reached a maximum at [K⁺]_o 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 - 34 mM.

 Key words: K⁺ channels, Lamprothamnium, I/V analysis, salt tolerance, hypotonic effect