Abstract
Fluid movement within the heart generates substantial shear forces, but the effect of this mechanical stress on the electrical activity of the human heart has not been examined. The fast component of the delayed rectifier potassium currents responsible for repolarization of the cardiac action potential, Ikr, is encoded by the human ether-a-go-go related gene (hERG) channel. Here, we exposed hERG1a channel-expressing HEK293T cells to laminar shear stress (LSS) and observed that this mechanical stress increased the whole-cell current by 30-40%. LSS shifted the voltage dependence of steady-state activation of the hERG channel to the hyperpolarizing direction, accelerated the time course of activation and recovery from inactivation, slowed down deactivation, and shifted the steady-state inactivation to the positive direction, all of which favored the hERG open state. In contrast, the time course of inactivation was faster, favoring the closed state. Using specific inhibitors of focal adhesion kinase, a regulator of mechano-transduction via the integrin pathway, we also found that the LSS-induced modulation of the whole-cell current depended on the integrin pathway. The hERG1b channel variant, which lacks the Per-Arnt-Sim (PAS) domain, and long QT syndrome-associated variants having point mutations in the PAS domain were unaffected by LSS, suggesting that the PAS domain in hERG1a channel may be involved in sensing mechanical shear stress. We conclude that a mechano-electric feedback pathway modulates hERG channel activity through the integrin pathway, indicating that mechanical forces in the heart influence its electrical activity.
Highlights
Fluid movement within the heart generates substantial shear forces, but the effect of this mechanical stress on the electrical activity of the human heart has not been examined
The hERG1b channel variant, which lacks the Per-ArntSim (PAS) domain, and long QT syndrome–associated variants having point mutations in the PAS domain were unaffected by laminar shear stress (LSS), suggesting that the PAS domain in hERG1a channel may be involved in sensing mechanical shear stress
The magnitude of shear stress experienced by a single cardiomyocyte in vivo in a working myocardium is difficult to determine [5]
Summary
The effect of laminar shear stress (LSS) on hERG-transfected HEK293T cells was investigated using the whole-cell patchclamp configuration in the voltage-clamp mode. We recorded hERG1a potassium currents in wholecell mode first under iso-osmotic conditions and under hypo-osmotic conditions for a period of 2.5 min to induce cell swelling at a constant flow rate of 1 ml/min (Fig. S4A). Individual data points at each given voltage are represented as mean Ϯ S.E. nificantly (p Ͼ 0.05, n ϭ 6, paired t test) between iso-osmotic (15.18 Ϯ 4.87 pF) and hypo-osmotic conditions (14.54 Ϯ 4.48 pF), which renders the fusion of channel containing vesicles with the plasma membrane an unlikely source of the increased current (Fig. S4B). A midpoint (V1/2) of Ϫ2.4 Ϯ 0.46 was observed after switching back to 1 ml/min flow rate, which is close to the pre-shear value (Fig. 2D, dashed lines, n ϭ 7).
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