Shear stress induces a longitudinal Ca2+ wave via autocrine activation of P2Y1 purinergic signalling in rat atrial myocytes

AbstractAtrial myocytes are exposed to shear stress during the cardiac cycle and haemodynamic disturbance. In response, they generate a longitudinally propagating global Ca²⁺ wave. Here, we investigated the cellular mechanisms underlying the shear stress‐mediated Ca²⁺ wave, using two‐dimensional confocal Ca²⁺ 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 Ca²⁺ 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 (IP₃Rs) abolished shear stress‐induced Ca²⁺ wave generation. Furthermore, in atrial myocytes from type 2 IP₃R (IP₃R2) knock‐out mice, shear stress failed to induce longitudinal Ca²⁺ waves. The phospholipase C (PLC) inhibitor {"type":"entrez-nucleotide","attrs":{"text":"U73122","term_id":"4098075","term_text":"U73122"}}U73122, but not its inactive analogue {"type":"entrez-nucleotide","attrs":{"text":"U73343","term_id":"1688125","term_text":"U73343"}}U73343, abolished the shear‐induced longitudinal Ca²⁺ wave. However, pretreating atrial cells with blockers for stretch‐activated channels, Na⁺−Ca²⁺ 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 P2Y₁ receptor antagonist MRS 2179, both suppressed the Ca²⁺ 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 Ca²⁺ to enhance hemichannel opening facilitated the wave generation. Our data suggest that longitudinally propagating, regenerative Ca²⁺ release through RyRs is triggered by P2Y₁–PLC–IP₃R2 signalling that is activated by gap junction hemichannel‐mediated ATP release in atrial myocytes under shear stress.

Abbreviations

9‐AC

9‐anthracenecarboxylic acid

2‐APB

2‐aminoethoxydiphenyl borate

CICR

Ca²⁺‐induced Ca²⁺ release

DPI

diphenyleneiodonium

FDHM

full duration at half‐maximum

IP₃R2

type 2 inositol 1,4,5‐trisphosphate receptor

KO

knock‐out

NCX

Na⁺−Ca²⁺ exchanger

NOX

nicotinamide adenine dinucleotide phosphate oxidase

PLC

phospholipase C

ROI

region‐of‐interest

RyR

ryanodine receptor

SAC

stretch‐activated channel

SR

sarcoplasmic reticulum

T_p

time‐to‐peak

TRPM4

transient receptor potential melastatin subfamily 4

V_p

propagation velocity

WT

wild‐type