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Resolution of hyposmotic stress in isolated mouse ventricular myocytes causes sealing of t‐tubules
Author(s) -
Moench I.,
Meekhof K. E.,
Cheng L. F.,
Lopatin A. N.
Publication year - 2013
Publication title -
experimental physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.925
H-Index - 101
eISSN - 1469-445X
pISSN - 0958-0670
DOI - 10.1113/expphysiol.2013.072470
Subject(s) - myocyte , osmotic shock , medicine , biophysics , electrophysiology , contraction (grammar) , chemistry , microbiology and biotechnology , endocrinology , anatomy , biology , biochemistry , gene
New Findings• What is the central question of this study? The t‐tubules of ventricular myocytes are critical elements in excitation–contraction coupling. They become disorganized or even lost in various cardiac pathologies. However, the mechanisms leading to disruption of t‐tubules are essentially unknown. This study was designed to identify physiologically relevant processes that underlie remodelling of t‐tubules. • What is the main finding and its importance? We show that the resolution of physiologically relevant hyposmotic swelling, not the application of osmotic shock itself, leads to dramatic t‐tubular remodelling, including the sealing of individual t‐tubules. The results point to an important and probably general mechanism of acute and fast stress‐induced t‐tubular remodelling that may underlie various relevant pathologies of the heart.It has recently been shown that various stress‐inducing manipulations in isolated ventricular myocytes may lead to significant remodelling of t‐tubules. Osmotic stress is one of the most common complications in various experimental and clinical settings. This study was therefore designed to determine the effects of a physiologically relevant type of osmotic stress, hyposmotic challenge, to the integrity of the t‐tubular system in mouse ventricular myocytes using the following two approaches: (1) electrophysiological measurements of membrane capacitance and inward rectifier ( I K1 ) tail currents originating from K + accumulation in t‐tubules; and (2) confocal microscopy of fluorescent dextrans trapped in sealed t‐tubules. Importantly, we found that removal of ‘0.6 Na’ (60% NaCl) hyposmotic solution, but not its application to myocytes, led to a ∼27% reduction in membrane capacitance, a ∼2.5‐fold reduction in the amplitude of the I K1 tail current and a ∼2‐fold reduction in the so‐called I K1 ‘inactivation’ (due to depletion of t‐tubular K + ) at negative membrane potentials; all these data were consistent with significant detubulation. Confocal imaging experiments also demonstrated that extracellularly applied dextrans become trapped in sealed t‐tubules only upon removal of hyposmotic solutions, i.e. during the shrinking phase, but not during the initial swelling period. In light of these data, relevant previous studies, including those on excitation–contraction coupling phenomena during hyposmotic stress, may need to be reinterpreted, and the experimental design of future experiments should take into account the novel findings.