Enhancement of S1P-induced contractile response in detrusor smooth muscle of rats having cystitis

Interstitial cystitis is a chronic disease characterized by lower abdominal pain and some nonspecific symptoms including an increase in urinary frequency and urgency. Sphingosine 1-phosphate (S1P) is a bioactive sphingolipid that controls smooth muscle tone via G-protein coupled receptors (S1P1-3 receptors). S1P production is known to take place both in physiological states and some pathological situations, such as in overactive bladder syndrome. The intracellular mechanism of S1P-induced contractile response was investigated in β-escin permeabilized detrusor smooth muscle of rats having cyclophosphamide-induced cystitis. The bladder was isolated from rats and detrusor smooth muscle strips were permeabilized with β-escin. S1P (50 µM)-induced contraction and calcium sensitization response were significantly increased in cystitis. S1P-induced augmented contractile response was inhibited by S1P2 receptor antagonist JTE-013 and S1P3 receptor antagonist suramin. S1P2 receptor protein expressions were increased in cystitis, where no change was observed in S1P3 expressions between control and cystitis groups. S1P-induced contraction was reduced by Rho kinase (ROCK) inhibitor Y-27632 and protein kinase C (PKC) inhibitor GF-109203X in both control and cystitis group. S1P-induced increased calcium sensitization response was decreased by ROCK inhibitor and PKC inhibitor in cystitis. Our findings provide the first evidence that interstitial cystitis triggers S1P-induced increase in intracellular calcium in permeabilized detrusor smooth muscle of female rats. Both S1P2 and S1P3 receptors are involved in S1P mediated enhanced contractile response. The augmentation in S1P-induced contraction in interstitial cystitis involves both PKC and ROCK pathways of calcium sensitization.