Sarcolemmal hydraulic conductivity of guinea-pig and rat ventricular myocytes

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 (L-p) was obtained by analyzing the time course of cell swelling and shrinkage in response to osmotic gradients. Results: Superfusion with aniosmotic solution (0.5-4 times normal osmolality) caused a rapid (<3 min to steady states) and reversible myocyte swelling or shrinkage, L-p was approximate to 1.9 x 10(10) l N-1 s(-1) for guinea-pig myocytes and 1.7 x 10(10) l N-1 s (1) for rat myocyte at 35degreesC. Arrhenius activation energy (E-a), a measure of the energy barrier to water flux. was approximate to 3.7 (guinea-pig) and approximate to 3.6 kcal mol (rat) between 11 and 35 degreesC: these values are equivalent to E-a of self-diffusion of water in bulk solution 1 (approximate to 4 kcal mol(-1)) Treatment with 0.1 mM Hg a sulfhydryl-oxidising reagent that blocks membrane water channels, reduced L-p was (approximate to) 80% and the sulfhydryl-reducing reagent dithiothreitol ( 10 mM) antagonized the inhibitory action of Hg2+. Inhibition of the volume-sensitive cation (30 muM Gd ) and anion ( 1 mM 4.4'-diisothiocyanostilbene-2.2'-disulfonate) channels and Na+-K+- pump (10 muM onabain) modified the size of osmotic, swelling, but had little effect on L-p. Conclusions: Although the obserxed L-p is relatively small in magnitude. the low E-a and the sulfhydryl reagent-induced modification of L-p, 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 path ways. i.e, the majority passing through water channels and the remainder penetrating the lipid bilayers. (C) 2002 Elsevier Science B.V. All rights reserved.