© 2002 by European Society of Cardiology
Copyright © 2002, European Society of Cardiology
Sarcolemmal hydraulic conductivity of guinea-pig and rat ventricular myocytes
Second Department of Physiology, Kanazawa Medical University, 1-1, Daigaku, Uchinada-machi, Kahoku-gun, Ishikawa-ken 920-0293, Japan
* Corresponding author. Tel.: +81-76-286-2211 (ext. 3644); fax: +81-76-286-8010 physiol2{at}kanazawa-med.ac.jp
Objective: Osmotic gradient-induced volume change and sarcolemmal water permeability of cardiac myocytes were evaluated to characterize the mechanism of water flux across the plasma membranes. Methods: Cell surface dimensions were measured from isolated guinea-pig and rat ventricular myocytes by digital videomicroscopy, and membrane hydraulic conductivity (Lp) was obtained by analyzing the time course of cell swelling and shrinkage in response to osmotic gradients. Results: Superfusion with anisosmotic solution (0.5–4 times normal osmolality) caused a rapid (<3 min to steady states) and reversible myocyte swelling or shrinkage. Lp was 
1.9x10–10 l N–1 s–1 for guinea-pig myocytes and 1.7x10–10 l N–1 s–1 for rat myocytes at 35 °C. Arrhenius activation energy (Ea), a measure of the energy barrier to water flux, was 3.7 (guinea-pig) and 3.6 kcal mol–1 (rat) between 11 and 35 °C; these values are equivalent to Ea of self-diffusion of water in bulk solution (4 kcal mol–1). Treatment with 0.1 mM Hg2+, a sulfhydryl-oxidizing reagent that blocks membrane water channels, reduced Lp by 80%, and the sulfhydryl-reducing reagent dithiothreitol (10 mM) antagonized the inhibitory action of Hg2+. Inhibition of the volume-sensitive cation (30 µM Gd3+) and anion (1 mM 4,4'-diisothiocyanostilbene-2,2'-disulfonate) channels and Na+–K+ pump (10 µM ouabain) modified the size of osmotic swelling but had little effect on Lp. Conclusions: Although the observed Lp is relatively small in magnitude, the low Ea and the sulfhydryl reagent-induced modification of Lp are characteristic of channel-mediated water transport. These data suggest that water flux across the sarcolemma of guinea-pig and rat heart cells occurs through parallel pathways, i.e., the majority passing through water channels and the remainder penetrating the lipid bilayers.
KEYWORDS Ion transport; Membrane permeability/physics; Membrane transport; Myocytes; Sarcolemma
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