Key result
Application of small membrane permeable molecules like DMSO (~140 mM) upon washout of hyposmotic solution reduced dextran trapping >3- to 4-fold and increased IK1,tail ~2-fold in mouse cardiomyocytes.
Small membrane permeable molecules like DMSO protect against osmotically induced t-tubule sealing in mouse ventricular myocytes, likely through membrane modification.
Does not support clinical use; hypothesis-generating for SMPM effects on t-tubule sealing in cardiac models.
Cardiac t-tubules are critical for efficient excitation-contraction coupling but become significantly remodeled during various stress conditions. However, the mechanisms by which t-tubule remodeling occur are poorly understood. Recently, we demonstrated that recovery of mouse ventricular myocytes after hyposmotic shock is associated with t-tubule sealing. In this study, we found that the application of Small Membrane Permeable Molecules (SMPM) such as DMSO, formamide and acetamide upon washout of hyposmotic solution significantly reduced the amount of extracellular dextran trapped within sealed t-tubules. The SMPM protection displayed sharp biphasic concentration dependence that peaks at ∼140 mM leading to >3- to 4-fold reduction in dextran trapping. Consistent with these data, detailed analysis of the effects of DMSO showed that the magnitude of normalized inward rectifier tail current (IK1,tail), an electrophysiological marker of t-tubular integrity, was increased ∼2-fold when hyposmotic stress was removed in the presence of 1% DMSO (∼140 mM). Analysis of dynamics of cardiomyocytes shrinking during resolution of hyposmotic stress revealed only minor increase in shrinking rate in the presence of 1% DMSO, and cell dimensions returned fully to prestress values in both control and DMSO groups. Application and withdrawal of 10% DMSO in the absence of preceding hyposmotic shock induced classical t-tubule sealing. This suggests that the biphasic concentration dependence originated from an increase in secondary t-tubule sealing when high SMPM concentrations are removed. Overall, the data suggest that SMPM protect against sealing of t-tubules following hyposmotic stress, likely through membrane modification and essentially independent of their osmotic effects.
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Uchida et al. (2016) studied Hyposmotic stress-induced t-tubule remodeling. Small Membrane Permeable Molecules (SMPM) such as DMSO, formamide and acetamide vs. Control (absence of SMPM) was evaluated on Amount of extracellular dextran trapped within sealed t-tubules and magnitude of normalized inward rectifier tail current (IK1,tail) (>3- to 4-fold reduction in dextran trapping; ~2-fold increase in IK1,tail). Application of small membrane permeable molecules like DMSO (~140 mM) upon washout of hyposmotic solution reduced dextran trapping >3- to 4-fold and increased IK1,tail ~2-fold in mouse cardiomyocytes.
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