Regulation of smooth muscle contractility by the epithelium in rat vas deferens: role of ATP‐induced release of PGE₂

Abstract

Recent studies suggest that the epithelium might modulate the contractility of smooth muscle. However, the mechanisms underlying this regulation are unknown. The present study investigated the regulation of smooth muscle contraction by the epithelium in rat vas deferens and the possible factor(s) involved. Exogenously applied ATP inhibited electrical field stimulation (EFS)-evoked smooth muscle contraction in an epithelium-dependent manner. As the effects of ATP on smooth muscle contractility were abrogated by inhibitors of prostaglandin synthesis, but not by those of nitric oxide synthesis, prostaglandins might mediate the effects of ATP. Consistent with this idea, PGE 2 inhibited EFS-evoked smooth muscle contraction independent of the epithelium, while ATP and UTP induced the release of PGE 2 from cultured rat vas deferens epithelial cells, but not smooth muscle cells. The ATP-induced PGE 2 release from vas deferens epithelial cells was abolished by U73122, an inhibitor of phospholipase C (PLC) and BAPTA AM, a Ca 2+ chelator. ATP also transiently increased [Ca 2+ ] i in vas deferens epithelial cells. This effect of ATP on [Ca 2+ ] i was independent of extracellular Ca 2+ , but abolished by the P2 receptor antagonist RB2 and U73122. In membrane potential measurements using a voltage-sensitive dye, PGE 2 , but not ATP, hyperpolarized vas deferens smooth muscle cells and this effect of PGE 2 was blocked by MDL12330A, an adenylate cyclase inhibitor, and the chromanol 293B, a blocker of cAMP-dependent K + channels. Taken together, our results suggest that ATP inhibition of vas deferens smooth muscle contraction is epithelium dependent. The data also suggest that ATP activates P2Y receptor-coupled Ca 2+ mobilization leading to the release of PGE 2 from epithelial cells, which in turn activates cAMP-dependent K + channels in smooth muscle cells leading to the hyperpolarization of membrane voltage and the inhibition of vas deferens contraction. Thus, the present findings suggest a novel regulatory mechanism by which the epithelium regulates the contractility of smooth muscle.

Role of Ca2+-activated K+ channels and Na+,K+-ATPase in prostaglandin E1- and E2-induced inhibition of the adrenergic response in human vas deferens

“…Consistent with our data, an acute stimulatory effect of PGE 1 and PGE 2 on Na + ,K + -ATPase activity was observed in rabbit renal proximal tubule cells and cortical collecting tubule of the nephron [35,36]. In rat vas deferens it has been demonstrated that PGE 2 is released from the epithelium in response to ATP stimulation and it is responsible for mediating the membrane hyperpolarization and inhibition of contraction of smooth muscle cells by activating cAMP-dependent K + channels [37]. However, our results show that PGE 2 inhibited neurogenic contractions but did not exert inhibitory effects on norepinephrine-induced contractions, indicating that PGE 2 acts directly on sympathetic nerve endings.…”

Infection by Toxoplasma gondii , a severe parasite in neonates and AIDS patients, causes impaired anion secretion in airway epithelia

“…The cells were grown in culture medium on six-well tissue plates with a piece of cover glass at 37°C. After 2 d of culture and T. gondii infection for 3 h and 6 h, the cells were prepared and loaded with the fluorescence dye Fluo 3/AM, as previously described (50). Data analysis was processed with Origin 8.0.…”

Regulation of Smooth Muscle Contraction by the Epithelium: Role of Prostaglandins

“…For the past few decades, several molecules have been recognized as the epitheliumderived relaxant/contractile factors, including PGs (55, 148), NO (16,65,159), ATP (25, 52), and endothelins (53, 74,110). Given their well documented effects on smooth muscle contraction and extensive involvement in many smooth musclemediated physiological functions (31,48,108,123,201), PGs appear to be one of the most important epithelium-derived factors.…”