Inhibitory Effects of Fatty Acids on Orai1-Mediated Contraction in Guinea Pig Gastric Fundus Smooth Muscle and Store-Operated Ca²⁺ Entry in 293T Cells

Abstract

Store-operated Ca²⁺ entry (SOCE), mediated by stromal interaction molecule (STIM) and Orai proteins, plays a key role in smooth muscle contraction. We previously demonstrated that docosahexaenoic acid (DHA) inhibits Orai1-dependent SOCE and suppresses contraction in guinea pig gastric fundus smooth muscle. However, whether this effect is specific to DHA or shared by other fatty acids remains unclear. In the present study, we examined the effects of thirteen fatty acids on cyclopiazonic acid (CPA)-induced contraction in gastric fundus smooth muscle and SOCE-associated Ca²⁺ responses in 293T cells. Among the fatty acids tested, γ-linolenic acid, pinolenic acid, eicosapentaenoic acid (EPA), and DHA significantly inhibited CPA-induced contraction. These fatty acids also suppressed SOCE-associated Ca²⁺ entry in wild-type 293T cells, with DHA showing the greatest effect. In STIM2-overexpressing 293T cells, pinolenic acid, EPA, and DHA inhibited SOCE-associated Ca²⁺ responses, whereas the inhibitory effect of γ-linolenic acid was lost. A structure–activity relationship was suggested, with inhibitory effects associated with the position of the first double bond relative to the carboxyl group (Δ4–Δ6). These findings suggest that fatty acids differentially inhibit SOCE, with pinolenic acid, EPA, and DHA showing consistent inhibitory effects across both 293T cell models, whereas γ-linolenic acid shows greater context dependence.