TRAM-34

Tofogliflozin is a sodium-glucose cotransporter 2 inhibitor widely used to treat type 2 diabetes mellitus, but it also exhibits cardio-protective effects. This study investigated the vasodilatory action of tofogliflozin using rabbit femoral artery rings pre-contracted with phenylephrine (1 μM). The results showed the concentration-dependent induction of vasodilation by tofogliflozin, a response that remained unchanged following endothelial removal, pretreatment with the nitric oxide synthase inhibitor L-NAME (100 μM), or the inhibition of low- and intermediate-conductance Ca²⁺-activated K⁺ channels using apamin (1 μM) in combination with TRAM-34 (1 μM). Furthermore, pretreatment with the voltage-dependent K⁺ (Kv) channel inhibitor 4-AP (3 mM) reduced the vasodilatory effects of tofogliflozin whereas pretreatment with the ATP-sensitive K⁺ channel inhibitor glibenclamide (10 μM) or the large-conductance Ca²⁺-activated K⁺ channel inhibitor paxilline (1 μM) did not. Notably, our findings indicated that Kv7.X, rather than Kv1.5 or Kv2.1, is the primary Kv subtype involved in tofogliflozin-induced vasodilation. The vasodilatory effects of tofogliflozin were also significantly inhibited in femoral arterial rings pretreated with the sarco/endoplasmic reticulum Ca²⁺-ATPase (SERCA) pump inhibitors thapsigargin (1 μM) and cyclopiazonic acid (10 μM). Tofogliflozin-induced vasodilation was unaltered in arterial rings exposed to the adenylyl cyclase inhibitor SQ 22536 (50 μM), the protein kinase A (PKA) inhibitor KT 5720 (1 μM), and the protein kinase G inhibitor KT 5823 (1 μM) whereas it was effectively reduced by the soluble guanylyl cyclase (sGC) inhibitor ODQ (10 μM). These findings suggest that tofogliflozin-induced vasodilation is mediated by the activation of the SERCA pump, the sGC/cGMP pathway, and Kv channels.

Atrial fibrillation (AF) is a prevalent cardiac arrhythmia characterized by atrial fibrosis which involves excessed proliferation and increased activity of fibroblast and myofibroblast, as well as alterations in the extracellular matrix (ECM). The specific mechanism driving fibrosis in atrial fibroblasts and myofibroblsats remains incompletely understood. This study investigates the role of the intermediate-conductance Ca²⁺-activated K⁺ channel (K_Ca3.1) in Angiotensin II (Ang II)-induced atrial fibrosis and elucidates the underlying mechanisms. Primary rat atrial fibroblasts/myofibroblasts were treated with Ang II to evaluate K_Ca3.1 expression, cells proliferation and ECM production. The involvement of ERK/NF-κB signaling pathway was assessed using specific inhibitors. Ang II treatment increased K_Ca3.1 expression, stimulated the proliferation of fibroblasts/myofibroblasts, and enhanced ECM production, effects that were attenuated by the Ang II receptor antagonist Losartan and the K_Ca3.1 inhibitor TRAM-34. Knockdown of K_Ca3.1 using siRNA significantly reduced Ang II-induced collagen synthesis, confirming its critical role in fibrosis. The ERK/NF-κB pathway was found to mediate Ang II-induced upregulation of K_Ca3.1, as evidenced by inhibition with specific inhibitors. In vivo, Ang II infusion in rats increased K_Ca3.1 expression and atrial fibrosis, with atria showing greater susceptibility to fibrosis compared to ventricle. These effects were mitigated by losartan and TRAM-34. In conclusion, our findings demonstrate that Ang II-induced upregulation of K_Ca3.1 through ERK/NF-κB pathway activation in atrial fibroblasts/myofibroblasts promotes cellular proliferation and collagen deposition, ultimately contributing to atrial fibrosis. K_Ca3.1 represents a promising therapeutic target for the treatment of atrial fibrosis in AF.