Reactive oxygen species are messengers in maintenance of human and guinea pig gallbladder tonic contraction

Abstract

The tonic contraction of human and guinea pig gallbladder (GB) is dependent on basal levels of PGE(2) and thromboxane A(2) (TxA(2)). The pathway involved in the genesis of these prostaglandins has not been elucidated. We aimed to examine the source of reactive oxygen species (ROS) and whether they contribute to the genesis of GB tonic contraction by generating basal prostaglandin levels. Tonic contraction was studied in human and guinea pig GB muscle strips treated with ROS scavengers (Tiron and catalase), apocynin (an inhibitor of NADPH oxidase), and NOX-1 small interference RNA (siRNA). The subunits of NADPH oxidase and their functional roles were determined with specific antibodies in GB muscle cells. ROS scavengers reduced the GB tonic contraction and H(2)O(2) and PGE(2) levels. Apocynin also inhibited the tonic contraction. Antibodies against subunits of NADPH oxidase present in GB muscle cells lowered H(2)O(2) and PGE(2) levels. NOX-1 siRNA transfection reduced the tonic contraction, NOX-1 expression, and levels of H(2)O(2) and PGE(2). Tiron and apocynin inhibited the expected increase in tension and H(2)O(2) levels induced by stretching of muscle strips. H(2)O(2) increased the levels of PGE(2) and TxA(2) by increasing platelet-activating factor-like lipids that phosphorylate p38 and cPLA(2) sequentially. H(2)O(2) generated by NADPH oxidase participates in a signal transduction pathway that maintains the GB tonic contraction by activating PAF, p38, and cPLA(2) to generate prostaglandins.

NK2 Receptor-Mediated Spontaneous Phasic Contractions in Normal and Ulcerative Colitis Human Sigmoid Colon

“…In normal muscle strips, catalase slightly reduced spontaneous phasic contractions, suggesting that a certain level of reactive oxygen species may contribute to maintenance of spontaneous phasic contractions. It has been shown that reactive oxygen species, generated by NADPH oxidase, contribute to the maintenance of tonic contraction in gallbladder (Cong et al, 2005).…”

Role of Subplasmalemmal Mitochondria in Angiotensin II–Mediated Contraction

“…In VSMCs from large arteries, Nox1 appears to be the most important agonist induced NADPH oxidase isoform 21 , while Nox2 may be more important in small-resistance arteries in vivo 22 . Using basilar and cerebral artery (a conductance vessel)-derived smooth muscle and the Nox1 inhibitor ML171, Chaplin et al demonstrated that Nox1 NADPH oxidase activity is necessary for local regulation of L-type Ca 2+ channels by AngII-induced H 2 O 2 micro-domain signaling.…”

Gallbladder nitric oxide

“…However, block of relaxation to EFS in strips from human gallbladder by a NOSI in vitro has been shown previously (6). This relaxation response has been controversial as it is small and is dependent on drug-induced tone level, and may be slow to develop and perhaps Cong et al (1) have not been convinced that this response is physiological in nature.…”

“…TO THE EDITOR: In their recent paper, Cong et al (1) argue that nitric oxide (NO) does not play a role in the relaxation of gallbladder muscle strips since a nitric oxide synthase inhibitor (NOSI) does not change gallbladder tonic contraction or block relaxation induced by electrical field stimulation (EFS). However, block of relaxation to EFS in strips from human gallbladder by a NOSI in vitro has been shown previously (6).…”