Orai1 Contributes to Platelet-Activating Factor (PAF)-Induced Contraction in Association with Voltage-Dependent Ca²⁺ Channel-Mediated Mechanisms in Guinea Pig Urinary Bladder Smooth Muscle

Abstract

Platelet-activating factor (PAF) is known to induce smooth muscle contraction; however, its mechanisms in urinary bladder smooth muscle (UBSM) remain unclear. We investigated the involvement of Orai1 in PAF-induced contraction in guinea pig UBSM. PAF (10⁻⁶ M)-induced contraction was markedly inhibited by the Orai1 inhibitor Synta66 (10⁻⁵ M) and the L-type voltage-dependent Ca²⁺ channel (VDCC) inhibitor verapamil (10⁻⁵ M). Similarly, under Ca²⁺-free conditions with store depletion induced by cyclopiazonic acid (3 × 10⁻⁵ M), Ca²⁺-induced contraction was suppressed by Synta66 and verapamil. In contrast, Synta66 only partially inhibited contractions induced by acetylcholine (10⁻⁵ M) and α,β-methylene ATP (3 × 10⁻⁶ M), and it had no effect on high-potassium chloride (80 mM)-induced contraction. Inhibition of Na⁺/Ca²⁺ exchanger 1 (NCX1), transient receptor potential canonical (TRPC) 1/4/5 channels, or anoctamin 1 (ANO1) did not significantly affect PAF-induced contraction. These findings suggest that Orai1 contributes to PAF-induced contraction in association with VDCC-dependent mechanisms, whereas NCX1, TRPC1/4/5 channels, and ANO1 play limited roles under these conditions.