Shear Stress Induces Transverse Ca2+ Waves via Autocrine Activation of P2X Purinoceptors in Rat Atrial Myocytes

Abstract

Atrial myocytes are exposed to high shear stress during blood regurgitation and high intra-atrial pressure due to valve diseases and heart failure, since such disturbances disrupt endocardium. We have previously reported that shear stress induces two types of global Ca2+ waves in atrial myocytes, longitudinal and transverse Ca2+ waves (T-waves) (Biophys J 2012;102(3, Suppl 1);227a), and that the longitudinal wave is triggered by Ca2+ release via P2Y1 purinoceptor-inositol 1,4,5-trisphosphate receptor signaling (J Physiol 2015;593:5091-5109). Here, we investigated cellular mechanism for the generation of T-wave in atrial cells under shear stress. Shear stress of ∼16 dyn/cm2 was applied onto single myocytes using micro fluid-jet, and two-dimensional confocal Ca2+ imaging was performed. Shear stress-induced T-waves were observed repetitively under 3-4 min intervals between the stimuli, and occurred at ∼1 event per 10 s. They were eliminated by inhibition of the voltage-gated Na+ or Ca2+ channels, or ryanodine receptors, suggesting that the T-wave is mediated by action potential-triggered Ca2+ release. Blockades of key stretch signaling molecules, stretch-activated channel, Na+-Ca2+ exchange, and NADPH oxidase, did not suppress T-wave generation by shear. However, shear-induced T-wave generation was abolished by pre-incubation of cells with external ATP-metabolizing enzyme apyrase, the gap junction blocker carbenoxolone, or with P2X purinoceptor antagonist iso-PPADS. Inhibition of P2Y1 purinergic signaling that mediates the longitudinal Ca2+ wave under shear did not attenuate the occurrence of T-waves. Our data suggest that shear stress induces activation of P2X purinoceptors via gap junction-mediated ATP release, thereby triggering action potential with subsequent T-wave in atrial myocytes.