Modeling the current-voltage characteristics of charophyte membranes. II. The effect of salinity on membranes of Lamprothamnium papulosum

Lamprothamnium is a salt-tolerant charophyte that inhabits a broad range of saline environments. The electrical characteristics of Lamprothamnium cell membranes were modeled in environments of different salinity: full seawate r (SW), 0.5 SW, 0.4 SW, and 0.2 SW. The cells were voltage-clamped to obtai n the IN (current-voltage) and GN (conductance-voltage) profiles of the cel l membranes. Cells growing at the different salinities exhibited one of thr ee types of IN profiles (states), pump-, background- and K+-states. This st udy concentrates on the pump- and background-states. Curved (pump-dominated ) I/V characteristics were found in cells with resting membrane PDs (potent ial differences) of -219 +/- 12 mV tin 0.2 SW: 6 cells, 16 profiles), -161 +/- 12 mV tin 0.4 SW: 6 cells, 7 profiles), -151 +/- 12 mV tin 0.5 SW: 6 ce lls, 12 profiles) and -137 +/- 12 mV tin full SW: 8 cells, 13 profiles). Th e linear I/V charac- teristics of the background-state were found in cells with resting PDs of -107 +/- 12 mV tin 0.4 SW: 7 cells, 12 profiles), -108 +/- 12 mV tin 0.5 SW: 7 cells, 10 profiles) and -104 +/- 12 mV tin full SW: 3 cells, 5 profiles). The resting conductance (G) of the cells progressive ly increased with salinity, from 0.5 S.m(-2) (in 0.2 SW) to 22.0 S.m(-2) ti n full SW). The pump peak conductance only rose from 2 S.m(-2) (0.2 SW) to 5 S.m(-2) (full SW), accounting for the increasingly depolarized resting PD observed in cells in more saline media. Upon exposure to hypertonic medium, both the pump and an inward K+ rectifie r were stimulated. The modeling of the I/V profiles identified the inward K + rectifier as an early electrical response to hypertonic challenge.