Cinnamaldehyde inhibits L-type calcium channels in mouse ventricular cardiomyocytes and vascular smooth muscle cells

Cinnamaldehyde (CA), a major component of cinnamon, is known to have important actions in the cardiovascular system, including vasorelaxation and decrease in blood pressure. Although CA-induced activation of the chemosensory cation channel TRPA1 seems to be involved in these phenomena, it has been shown that genetic ablation of Trpa1 is insufficient to abolish CA effects. Here, we confirm that CA relaxes rat aortic rings and report that it has negative inotropic and chronotropic effects on isolated mouse hearts. Considering the major role of L-type Ca²⁺ channels in the control of the vascular tone and cardiac contraction, we used whole-cell patch-clamp to test whether CA affects L-type Ca²⁺ currents in mouse ventricular cardiomyocytes (VCM, with Ca²⁺ as charge carrier) and in mesenteric artery smooth muscle cells (VSMC, with Ba²⁺ as charge carrier). We found that CA inhibited L-type currents in both cell types in a concentration-dependent manner, with little voltage-dependent effects. However, CA was more potent in VCM than in VSMC and caused opposite effects on the rate of inactivation. We found these divergences to be at least in part due to the use of different charge carriers. We conclude that CA inhibits L-type Ca²⁺ channels and that this effect may contribute to its vasorelaxing action. Importantly, our results demonstrate that TRPA1 is not a specific target of CA and indicate that the inhibition of voltage-gated Ca²⁺ channels should be taken into account when using CA to probe the pathophysiological roles of TRPA1.