Modeling current-voltage (I/V) Modeling current-voltage (I/V) characteristics of salt-tolerant characteristics of salt-tolerant

charophyte charophyte LamprothamniumLamprothamnium in in steady state and at the time of steady state and at the time of

turgor regulationturgor regulation

Mary J Beilby and Virginia A. Shepherd

School of Physics, Biophysics, The University of NSW, Sydney Australia

Materials and Methods

amplifier

MembranePD

Voltagecommands

Membranecurrent

Current–voltage analysis

1sec

0 PD200 mV

0 current

4 A

Modeling6 cells in 1/3 seawater: pump state

ibackground = gbackground (V – Vbackground)

7 cells in background state

165):63 JMB 1981, al.et (Hansen model HGSS

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0.2 SW 77.0 2.0 86.0 140.5

Medium Na+ K+ Cl- osmolarity

mM mM mM mOsmol.kg-1

0.4 SW 154.0 4.1 172.0 281.0

0.5 SW 175.0 8.0 201.0 536.0

full SW 350.0 16.0 400.0 1072.0

Steady state I/V characteristics in range of salinities

For details see:Beilby and Shepherd, 2001, J. Membrane Biol. 181: 77

Hypertonic regulation:from 0.2 SW to 0.4 SW

time:

5 min

21 min

41 min

2 hr 34 min

3 hr 30 min

Modeling 0.5 SW, 9 mM K+: cell in K+ state

ibackground = gbackground (V – Vbackground)

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Hypotonic regulation: 1/3 SW to 1/6 SW cell in K+ state, Cl- current inhibited by La3+

time:

3 min

10 min

12 min

15 min

22 min

85 min

(For details see: Beilby and Shepherd, 2001, Aust. J. Plant Physiol. 28: 541- 550 )

ConclusionsConclusions• Steady state conductance rises with salinity mainly due to ibackground, Vbackground is not affected by salinity

• Hypertonic regulation turns on iirc before ipump

iirc is carried by K+.

• Hypotonic regulation turns on iK independently of iCl

• The increase in [K+]cyt precedes rise in NKPK

• Vbackground depolarizes and gbackground increases at the time of hypotonic regulation

• The proton pump works harder to keep the membrane PD negative in more saline media

Future workFuture workTransporter for ibackground? H+ channels? Stretch activated channels?

Is iirc the detector of hypertonic stress?

Electroneutrality ?

Signal for tonoplast K+ channels to open ?

H+ channels involved in hypotonic regulation?

What is the limiting pump conductance?

This presentation can be found on http://www.phys.unsw.edu.au/~mjb/