Potentiation of stretch-induced tone in the rabbit facial vein by an isoquinoline derivative, LOE 908

Inhibitory mechanisms of docosahexaenoic acid on carbachol-, angiotensin II-, and bradykinin-induced contractions in guinea pig gastric fundus smooth muscle

We studied the inhibitory actions of docosahexaenoic acid (DHA) on the contractions induced by carbachol (CCh), angiotensin II (Ang II), and bradykinin (BK) in guinea pig (GP) gastric fundus smooth muscle (GFSM), particularly focusing on the possible inhibition of store-operated Ca2+ channels (SOCCs). DHA significantly suppressed the contractions induced by CCh, Ang II, and BK; the inhibition of BK-induced contractions was the strongest. Although all contractions were greatly dependent on external Ca2+, more than 80% of BK-induced contractions remained even in the presence of verapamil, a voltage-dependent Ca2+ channel inhibitor. BK-induced contractions in the presence of verapamil were not suppressed by LOE-908 (a receptor-operated Ca2+ channel (ROCC) inhibitor) but were suppressed by SKF-96365 (an SOCC and ROCC inhibitor). BK-induced contractions in the presence of verapamil plus LOE-908 were strongly inhibited by DHA. Furthermore, DHA inhibited GFSM contractions induced by cyclopiazonic acid (CPA) in the presence of verapamil plus LOE-908 and inhibited the intracellular Ca2+ increase due to Ca2+ addition in CPA-treated 293T cells. These findings indicate that Ca2+ influx through SOCCs plays a crucial role in BK-induced contraction in GP GFSM and that this inhibition by DHA is a new mechanism by which this fatty acid inhibits GFSM contractions.

Platelet-activating factor (PAF) enhances guinea pig detrusor smooth muscle contractile activities by stimulating voltage-dependent Ca2+ channels and store-operated Ca2+ channels

We investigated the extracellular Ca²⁺ influx pathways involved in platelet-activating factor (PAF)-enhanced guinea pig detrusor smooth muscle (DSM) contractile activities. One micromolar PAF-enhanced DSM contractile activities were completely inhibited by extracellular Ca²⁺ removal and strongly suppressed by voltage-dependent Ca²⁺ channel (VDCC) inhibitors. PAF-enhanced DSM contractile activities remaining in the presence of verapamil (10 μM) were not inhibited by LOE-908 (30 μM, an inhibitor of receptor-operated Ca²⁺ channels (ROCCs)), but were almost completely inhibited by SKF-96365 (30 μM, an inhibitor of store-operated Ca²⁺ channels (SOCCs) and ROCCs). These results suggest that VDCCs and SOCCs are responsible for PAF-enhanced DSM contractile activities.

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, PGF_2α, 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.