Summary

The electrical characteristics of Lamprothamnium membranes were modelled in range of media salinities: 1/5, 1/3, 1/2 and full seawater (SW). The cells were voltage-clamped to obtain the I/V (current-voltage) and G/V(conductance-voltage) profiles of the cell membranes. In most salinities the cells exhibited three types of I/V profiles: pump, background and K⁺ states. This study concentrates on the first two states.

The cells grown at each salinity displayed curved pump-dominated I/V characteristics with resting PDs (potential differences) of -219 (range 24 mV) (1/5 SW: 6 cells, 16 pofiles), -161 (range 24 mV) (1/3 SW: 6 cells, 7 profiles), -151 (range 24 mV) (1/2 SW: 6 cells, 12 profiles) and -137 (range 24 mV) (full SW: 8 cells, 13 profiles). The cells in background state showed linear I/V characteristics with resting PDs of -107 (range 24 mV) (1/3 SW: 7 cells, 12 profiles), -108 (range 24 mV) (1/2 SW: 7 cells, 10 profiles) and -104 (range 24 mV) (full SW: 3 cells, 5 profiles). Modelling of the I/V profiles indicated that the background conductance increased from 0.5 S.m^-2 (1/5 SW) to 22.0 S.m^-2 (full SW). The pump peak conductance only rose from 2 S.m^-2 (1/5 SW) to 5 S.m^-2 (full SW), accounting for the increasingly less hyperpolarised resting PD observed in cells in more saline media.

Upon exposure to hypertonic medium, both the pump and the inward rectifier were stimulated. The I/V profiles were modelled, yielding details of hypertonic turgor regulation.

 Key words: salinity, Lamprothamnium, current-voltage profiles, pump model, hypertonic effect.