ABSTRACT
The NMR (nuclear magnetic resonance) method of Conlon and Outhred (1972) was used to measure diffusional water permeability of the nodal cells of the green alga Chara gymnophylla. Two local minima at 15 and 30 degreesC of diffusional water permeability (Pd) were observed delimiting a region of low activation energy (Ea around 20 kJ/mol) indicative of an optimal temperature region for membrane transport processes. Above and below this region water transport was of a different type with high Ea (about 70 kJ/mol). The triphasic temperature dependence of the water transport suggested a channel-mediated transport at 15-30 degreesC and lipid matrix-mediated transport beyond this region. The K+ channel inhibitor, tetraethylammonium as well as the Cl- channel inhibitor, ethacrynic acid, diminished Pd in the intermediate temperature region by 54 and 40%, respectively. The sulfhydryl agent p-(chloromercuri-benzensulfonate) the water transport inhibitor in erythrocytes also known to affect K+ transport in Chara, only increased Pd below 15 degreesC. In high external potassium ('K-state') water transport minima were pronounced. The role of K+ channels as sensors of the optimal temperature limits was further emphasized by showing a similar triphasic temperature dependence of the conductance of a single K+ channel also known to cotransport water, which originated from cytoplasmic droplets (putatively tonoplast) of C. gymnophylla. The minimum of K+ single channel conductance at around 15 degreesC, unlike the one at 30 degreesC, was sensitive to changes of growth temperature underlining membrane lipid involvement. The additional role of intracellular (membrane?) water in the generation of discontinuities in the above thermal functions was suggested by an Arrhenius plot of the cellular water relaxation rate which showed breaks at 13 and 29 degreesC.
Subject(s)
Chlorophyta/metabolism , Ion Transport/physiology , Temperature , Water/metabolism , 4-Chloromercuribenzenesulfonate/pharmacology , Chlorophyta/drug effects , Deuterium Oxide/metabolism , Enzyme Inhibitors/pharmacology , Ethacrynic Acid/pharmacology , Gadolinium DTPA/metabolism , In Vitro Techniques , Ion Transport/drug effects , Magnetic Resonance Spectroscopy , Mercuric Chloride/pharmacology , Molecular Probes/metabolism , Patch-Clamp Techniques , Potassium Channels/physiology , Potassium Chloride/pharmacology , Signal Transduction , Sulfhydryl Reagents/pharmacology , Tetraethylammonium/pharmacologyABSTRACT
Comparative NMR studies of normal and pathologically altered human stomach tissues were performed on the basis of proton T1 relaxation time measurements in the presence of high external concentrations of relaxation (contrast) agents manganese ethylenediaminetetraacetic acid (Mn-EDTA) and gadolinium diethylenetriaminepentaacetic acid (Gd-DTPA). Diffusion permeability of the cell membrane to water, Pd, was determined by measuring the longest proton T1 component sensitive to the exchange of water molecules through the cell membrane. Pathologically altered tissues showed substantially higher (2 to 10 times) average cell membrane permeabilities to water.
