Osmometric and Water-Transporting Properties of Guinea Pig Cardiac Myocytes.

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To elucidate the mechanism of water flux across heart cell membranes, osmotically induced volume changes and sarcolemmal water permeability were evaluated in isolated guinea pig ventricular myocytes by videomicroscopic measurements of cell surface dimensions. Superfusion with anisosmotic solution (0.5–4 times normal osmolality) caused a rapid (lt;3 min to new steady state) and reversible cell swelling or shrinkage mainly because of proportional changes in cell width and thickness. The van't Hoff relationship between relative cell volume and the reciprocal of relative osmolality was linear and predicted an apparent osmotically dead space of ~35% cell volume. The osmotic water permeability coefficient (Pf) measured from the time course of cell swelling/shrinkage was ~22 μm·s−1 at 35°C. Arrhenius activation energy (Ea), a measure of the energy barrier to water flux, was ~3.8 kcal·mol−1 between 11 and 35°C; this value is equivalent to Ea for free-water diffusion in bulk solution (~4 kcal·mol−1). Treatment with 0.1 mM Hg2+, a sulfhydryl-oxidizing reagent, reduced Pf by ~90%, and the sulfhydryl-reducing reagent dithiothreitol (10 mM) antagonized the inhibitory action of Hg2+. Ea measured from Hg2+-treated myocytes (12.3 kcal·mol−1) was in the range of that for diffusional water movement through the lipid bilayers (>10 kcal·mol−1). Although the observed Pf is small in magnitude, both the low Ea and the sulfhydryl-related modifications of Pf are characteristic of channel-mediated water transport. These data suggest that water channels form a major conduit for water crossing the sarcolemma of guinea-pig heart cells.<br>

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