Pharmacological study on the enhancing effects of U46619 on guinea pig urinary bladder smooth muscle contraction induced by acetylcholine and α,ß-methylene ATP and the possible involvement of protein kinase C.

We examined whether U46619 (a prostanoid TP receptor agonist) could enhance the contractions of guinea pig urinary bladder smooth muscle (UBSM) in response to acetylcholine (ACh) and an ATP analog (α,ß-methylene ATP (αß-MeATP)) through stimulation of the UBSM TP receptor and whether protein kinase C (PKC) is involved. U46619 (10-7 M) markedly enhanced UBSM contractions induced by electrical field stimulation and ACh/αß-MeATP (3 × 10-6 M each), the potentiation of which was completely suppressed by SQ 29,548 (a TP receptor antagonist, 6 × 10-7 M). PKC inhibitors did not attenuate the ACh-induced contractions enhanced by U46619 although they partly suppressed the U46619-enhanced, αß-MeATP-induced contractions. While phorbol 12-myristate 13-acetate (PMA, a PKC activator, 10-6 M) did not enhance ACh-induced contractions, it enhanced αß-MeATP-induced contractions, an effect that was completely suppressed by PKC inhibitors. αß-MeATP-induced contractions, both with and without U46619 enhancement, were strongly inhibited by diltiazem. U46619/PMA enhanced 50 mM KCl-induced contractions, the potentiation of which was partly/completely attenuated by PKC inhibitors. These findings suggest that U46619 potentiates parasympathetic nerve-associated UBSM contractions by stimulating UBSM TP receptors. PKC-increased Ca2+ influx through voltage-dependent Ca2+ channels may partially play a role in purinergic receptor-mediated UBSM contractions enhanced by TP receptor stimulation.

Docosahexaenoic acid and eicosapentaenoic acid strongly inhibit prostanoid TP receptor-dependent contractions of guinea pig gastric fundus smooth muscle.

The inhibitory effects of docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA), and linoleic acid (LA) on the contractions induced by five prostanoids and U46619 (a TP receptor agonist) were examined in guinea pig gastric fundus smooth muscle (GFSM). Tension changes were isometrically measured, and the mRNA expression of prostanoid receptors was measured by RT-qPCR. DHA and EPA significantly inhibited contractions induced by the prostanoids and U46619, whereas LA inhibited those induced by prostaglandin D2 and U46619. The mRNA expression levels of the prostanoid receptors were TP ≈ EP3  >> FP > EP1 . The inhibition by DHA, EPA, and LA was positively correlated with that by SQ 29,548 (a TP receptor antagonist) but not with that by L-798,106 (an EP3 receptor antagonist). DHA and EPA suppressed high KCl-induced contractions by 35% and 25%, respectively, and the contractions induced by the prostanoids and U46619 were suppressed by verapamil, a voltage-dependent Ca2+ channel (VDCC) inhibitor, by 40%-85%. Although LA did not suppress high KCl-induced contractions, it suppressed U46619-induced contractions in the presence of verapamil. However, LA did not show significant inhibitory effects on U46619-induced Ca2+ increases in TP receptor-expressing cells. In contrast, LA inhibited U46619-induced contractions in the presence of verapamil, which was also suppressed by SKF-96365 (a store-operated Ca2+ channel [SOCC] inhibitor). These findings suggest that the TP receptor and VDCC are targets of DHA and EPA to inhibit prostanoid-induced contractions of guinea pig GFSM, and SOCCs play a significant role in LA-induced inhibition of U46619-induced contractions.

Prostanoid TP receptor stimulation enhances contractile activities in guinea pig urinary bladder smooth muscle through activation of Ca2+ entry channels: Potential targets in the treatment of urinary bladder contractile dysfunction.

AIMS: We examined the potential stimulatory effects of U46619 (a prostanoid TP receptor agonist) and five prostanoids on the contractile activities of urinary bladder smooth muscle (UBSM), focusing on the role of the TP receptor and its associated Ca2+ influx routes to understand the roles of prostanoids in the regulation of UB contractile activity. MAIN METHODS: Changes in the basal tone and spontaneous contractile activity (amplitude and frequency) of isolated guinea pig UBSM were measured isotonically. The presence of TP receptors in UBSM was examined by RT-qPCR and immunofluorescence. KEY FINDINGS: U46619, prostaglandin (PG) E2, PGF2α, and PGA2 enhanced UBSM basal tone and spontaneous contractile activities, which were measured as amplitudes and frequencies. The enhancing effects of U46619 were completely suppressed by SQ 29,548 (a TP receptor antagonist), which also partially suppressed the stimulating effects of other prostanoids. The expression of TP receptors in UBSMs was verified at the mRNA and protein level. The enhancing effects of U46619 completely disappeared in Ca2+-free solution. U46619-enhanced basal tone was completely suppressed by verapamil, an inhibitor of voltage-dependent Ca2+ channels (VDCCs), and verapamil strongly decreased the spontaneous contraction frequency. The spontaneous contractions remaining in the presence of verapamil were strongly suppressed by SKF-96365 (an inhibitor of receptor-operated Ca2+ channels (ROCCs)/store-operated Ca2+ channels (SOCCs)), but not by LOE-908 (an inhibitor of ROCCs). SIGNIFICANCE: Prostanoids can enhance UBSM contractile activities and thus may be endogenous candidates for induction of detrusor overactivity. The TP receptor and TP-receptor-activated VDCCs/SOCCs are key molecules responsible for these effects.