Possible mechanisms underlying the biphasic regulatory effects of arachidonic acid on Ca2Â + signaling in HEK293 cells

► Mechanisms for arachidonic acid (AA) regulating Ca2+ signal. ► Low concentration AA reduces cell membrane fluidity and Ca2+ response to agonist. ► High concentration AA increases sarcolemma fluidity and induces Ca2+ influx. ► Gd3+ abolishes AA-mediated Ca2+ signal independent of membrane stabilization. ► Lowered fluidity for inhibitory effect, Gd3+-sensitive pore for Ca2+ signal of AA.