Stretch-Induced Increase in Ca<SUP>2+</SUP>-Spark Rate in Rabbit Atrial Cardiomyocytes Requires TRPA1 and Intact Microtubule Network

Background Mechanical stretch of the myocardium is proarrhythmic and alters cellular Ca2+ handling, potentially involving cation nonselective mechano-sensitive ion channels. This study aimed to assess the presence and mechanisms of stretch-induced increase in Ca2+-spark rate (SiS) in isolated atrial cardiomyocytes.Methods Freshly isolated rabbit, pig, and human left atrial cardiomyocytes were stretched axially using glass microrods. Free cytosolic Ca2+ concentration was monitored using confocal microscopy at resting sarcomere length (approximate to 1.79 mu m) and during severe (approximate to 12%) increase in sarcomere length.Results Diastolic stretch provoked SiS, which was prevented by disrupting microtubules with colchicine, but unaffected by inhibition of NADPH oxidase 2 or scavenging of reactive oxygen species. SiS was absent in Na+- and Ca2+-free external solution, suggesting that it requires transsarcolemmal influx of Na+ or Ca2+. Activation of Piezo1 increased baseline spark rate, which was further increased by stretch. TRPA1 (transient receptor potential ankyrin 1) activation also increased baseline spark rate, with no further change upon stretch. SiS was not detectable in the presence of streptomycin (a blocker of nonselective mechano-sensitive ion channels), and HC-030031 and A-967079 (selective blockers of TRPA1), even when Piezo1 was activated. SiS was also observed in pig and human atrial cardiomyocytes.Conclusions In atrial cardiomyocytes, diastolic stretch enhances Ca2+-spark rate through a mechanism that requires microtubular integrity and TRPA1 but that is independent of redox signaling. TRPA1 emerges as a key regulator of stretch-induced Ca2+ handling in atrial cells, with potential implications for arrhythmogenesis.