TY - JOUR
T1 - Active trans-plasma membrane water cycling in yeast is revealed by NMR
AU - Zhang, Yajie
AU - Poirier-Quinot, Marie
AU - Springer, Charles S.
AU - Balschi, James A.
N1 - Funding Information:
National Institutes of Health grants HL078634 (J.A.B.), EB-00422, and NS-40801 (C.S.S.) supported this work.
PY - 2011/12/7
Y1 - 2011/12/7
N2 - Plasma membrane water transport is a crucial cellular phenomenon. Net water movement in response to an osmotic gradient changes cell volume. Steady-state exchange of water molecules, with no net flux or volume change, occurs by passive diffusion through the phospholipid bilayer and passage through membrane proteins. The hypothesis is tested that plasma membrane water exchange also correlates with ATP-driven membrane transport activity in yeast (Saccharomyces cerevisiae). Longitudinal 1H 2O NMR relaxation time constant (T 1) values were measured in yeast suspensions containing extracellular relaxation reagent. Two-site-exchange analysis quantified the reversible exchange kinetics as the mean intracellular water lifetime (τ i), where τ i -1 is the pseudo-first-order rate constant for water efflux. To modulate cellular ATP, yeast suspensions were bubbled with 95%O 2/5%CO 2 (O 2) or 95%N 2/5%CO 2 (N 2). ATP was high during O 2, and τ i -1 was 3.1 s -1 at 25°C. After changing to N 2, ATP decreased and τ i -1 was 1.8 s -1. The principal active yeast ion transport protein is the plasma membrane H +-ATPase. Studies using the H +-ATPase inhibitor ebselen or a yeast genetic strain with reduced H +-ATPase found reduced τ i -1, notwithstanding high ATP. Steady-state water exchange correlates with H +-ATPase activity. At volume steady state, water is cycling across the plasma membrane in response to metabolic transport activity.
AB - Plasma membrane water transport is a crucial cellular phenomenon. Net water movement in response to an osmotic gradient changes cell volume. Steady-state exchange of water molecules, with no net flux or volume change, occurs by passive diffusion through the phospholipid bilayer and passage through membrane proteins. The hypothesis is tested that plasma membrane water exchange also correlates with ATP-driven membrane transport activity in yeast (Saccharomyces cerevisiae). Longitudinal 1H 2O NMR relaxation time constant (T 1) values were measured in yeast suspensions containing extracellular relaxation reagent. Two-site-exchange analysis quantified the reversible exchange kinetics as the mean intracellular water lifetime (τ i), where τ i -1 is the pseudo-first-order rate constant for water efflux. To modulate cellular ATP, yeast suspensions were bubbled with 95%O 2/5%CO 2 (O 2) or 95%N 2/5%CO 2 (N 2). ATP was high during O 2, and τ i -1 was 3.1 s -1 at 25°C. After changing to N 2, ATP decreased and τ i -1 was 1.8 s -1. The principal active yeast ion transport protein is the plasma membrane H +-ATPase. Studies using the H +-ATPase inhibitor ebselen or a yeast genetic strain with reduced H +-ATPase found reduced τ i -1, notwithstanding high ATP. Steady-state water exchange correlates with H +-ATPase activity. At volume steady state, water is cycling across the plasma membrane in response to metabolic transport activity.
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U2 - 10.1016/j.bpj.2011.10.035
DO - 10.1016/j.bpj.2011.10.035
M3 - Article
C2 - 22261073
AN - SCOPUS:82955169484
SN - 0006-3495
VL - 101
SP - 2833
EP - 2842
JO - Biophysical Journal
JF - Biophysical Journal
IS - 11
ER -