Shear stress induces a longitudinal Ca ²⁺ wave via autocrine activation of P2Y ₁ purinergic signalling in rat atrial myocytes

Abstract

Key points

• Cardiac myocytes are subjected to fluid shear stress during the cardiac cycle and haemodynamic disturbance.

• A longitudinally propagating, regenerative Ca ²⁺ wave is initiated in atrial myocytes under shear stress.

• Here we determine the cellular mechanism for this shear‐induced Ca ²⁺ wave using two‐dimensional confocal Ca ²⁺ imaging combined with pressurized fluid flow.

• Our data suggest that shear stress triggers the Ca ²⁺ wave through ryanodine receptors via P2Y ₁ purinoceptor–phospholipase C‐type 2 inositol 1,4,5‐trisphosphate receptor signal transduction in atrial myocytes, and that this mechanotransduction is activated by gap junction hemichannel‐mediated ATP release.

• Shear‐specific mechanotransduction and the subsequent regenerative Ca ²⁺ wave may be one way for atrial myocytes to assess mechanical stimuli directly and alter their Ca ²⁺ signalling accordingly.

Abstract

Atrial myocytes are exposed to shear stress during the cardiac cycle and haemodynamic disturbance. In response, they generate a longitudinally propagating global Ca ²⁺ wave. Here, we investigated the cellular mechanisms underlying the shear stress‐mediated Ca ²⁺ wave, using two‐dimensional confocal Ca ²⁺ imaging combined with a pressurized microflow system in single rat atrial myocytes. Shear stress of ∼16 dyn cm ⁻² for 8 s induced ∼1.2 aperiodic longitudinal Ca ²⁺ waves (∼79 μm s ⁻¹) with a delay of 0.2−3 s. Pharmacological blockade of ryanodine receptors (RyRs) or inositol 1,4,5‐trisphosphate receptors (IP ₃Rs) abolished shear stress‐induced Ca ²⁺ wave generation. Furthermore, in atrial myocytes from type 2 IP ₃R (IP ₃R2) knock‐out mice, shear stress failed to induce longitudinal Ca ²⁺ waves. The phospholipase C (PLC) inhibitor U73122, but not its inactive analogue U73343, abolished the shear‐induced longitudinal Ca ²⁺ wave. However, pretreating atrial cells with blockers for stretch‐activated channels, Na ⁺−Ca ²⁺ exchanger, transient receptor potential melastatin subfamily 4, or nicotinamide adenine dinucleotide phosphate oxidase did not suppress wave generation under shear stress. The P2 purinoceptor inhibitor suramin, and the potent P2Y ₁ receptor antagonist MRS 2179, both suppressed the Ca ²⁺ wave, whereas the P2X receptor antagonist, iso‐PPADS, did not alter it. Suppression of gap junction hemichannels permeable to ATP or extracellular application of ATP‐metabolizing apyrase inhibited the wave. Removal of external Ca ²⁺ to enhance hemichannel opening facilitated the wave generation. Our data suggest that longitudinally propagating, regenerative Ca ²⁺ release through RyRs is triggered by P2Y ₁–PLC–IP ₃R2 signalling that is activated by gap junction hemichannel‐mediated ATP release in atrial myocytes under shear stress.