Modulation of Ca(2+) homoeostasis in cardiac myocytes plays a major role in beat-to-beat regulation of heart function. Previous studies suggest that sphingosine-1-phosphate (S1P), a biologically active sphingomyelin metabolite, regulates Ca(2+) handling in cardiac myocytes, but the underlying mechanism is unclear. In the present study, we tested the hypothesis that S1P-induced functional alteration of intracellular Ca(2+) handling includes the L-type calcium channel current (ICa,L) via a signalling pathway involving P21-activated kinase 1 (Pak1). Our results show that, in rat ventricular myocytes, S1P (100 nM) does not affect the basal activity of ICa,L but is able to partially reverse the effect of the β-adrenergic agonist Isoproterenol (ISO, 100 nM) on ICa,L. S1P (25 nM) also significantly prevents ISO (5 nM)-induced Ca(2+) waves and diastolic Ca(2+) release in these cells. Our further molecular characterisation demonstrates that Pak1 activity is increased in myocytes treated with S1P (25 nM) compared with those myocytes without treatment of S1P. By immunoprecipitation we demonstrate that Pak1 and protein phosphatase 2A (PP2A) are associated in ventricular tissue indicating their functional interaction. Thus the results indicate that S1P attenuates β-adrenergic stress-induced alteration of intracellular Ca(2+) release and L-type Ca(2+) channel current at least in part via Pak1-PP2A-mediated signalling.

Evidence accumulated over the past decade suggests that p21-activated kinase 1 (PAK1) is a critical cardiac-protective signalling molecule. The present article provides an updated review of recent findings regarding the role of PAK1 in maintaining normal cardiac electrophysiological function through its regulation of membrane and Ca 2+ clocks. We first overviewed the PAK1 activation mechanism. We then discussed recent updated results showing the action mechanisms of PAK1 signalling on Cav1.2/Cav1.3 (I CaL )-mediated Ca 2+ entry, ryanodine receptor type 2-mediated sarcoplasmic reticulum (SR) Ca 2+ release, transcriptional regulation of SR Ca 2+ -ATPase 2a, Na + /Ca 2+ exchangers, and Ca 2+ /calmodulin-dependent protein kinase II. Finally, we proposed a new and exciting route for developing a PAK1-based therapeutic strategy for cardiac arrhythmias. This article is part of the theme issue ‘The heartbeat: its molecular basis and physiological mechanisms’.