We previously showed that complete loss of smooth muscle myosin heavy chain isoform 2 (SM2) resulted in postnatal lethality, but in het mice a partial loss of SM2 (SM2+/–) was accompanied by down-regulation of SM1 with unaltered SM2:SM1 ratio. To determine whether a normal bladder function would be maintained throughout its lifespan, we aged WT and SM2+/– mice up to 18 months and analyzed a) SM2:SM1 ratio b) bladder smooth muscle structure and c) function in SM2+/– het mice. A notable finding was that ~50% of 15–18 months old male SM2+/– mice exhibited urinary retention in bladder with the distention of upper urethra. In SM2+/– mouse bladder with urinary retention, the SM2:SM1 ratio was decreased but not in SM2+/– mouse bladder that did not develop urinary retention. Interestingly in the distended bladder the expression levels of α-actin and tropomyosin remained unaltered despite a reduction in the number of myosin thick filaments. These distended bladders showed hypersensitivity to submaximal K+ depolarization and M3-receptor stimulation, without a significant increase in myosin light chain phosphorylation. We therefore suggest that a partial loss of SM2 may predispose male mice to develop lower urinary tract obstruction during ageing. In addition our data suggest that bladder obstruction can cause a further reduction in SM2 expression and SM2:SM1 ratio, and a hyper-contractility of the bladder smooth muscle.

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Omeprazole, a proton pump inhibitor, is widely used for the treatment of patients with peptic ulcer, gastroesophageal reflux disease and functional dyspepsia (FD), although some studies have demonstrated that omeprazole delays gastric emptying. The purpose of this study was to investigate the efficacy of omeprazole on gastric motility including gastric myoelectrical activity and gastric emptying. This study was performed on 12 healthy volunteers. Gastric motility was evaluated with cutaneously recorded electrogastrography (EGG) and gastric emptying of semi-solid meals using the ¹³C-acetic acid breath test. EGG and gastric emptying were measured before and after treatment with 20 mg omeprazole orally for 7 days. In the fasting state, the percentage of EGG normogastria increased significantly compared to the baseline. No significant changes were observed in other EGG parameters including the percentage of tachygastria and bradygastria in both fasting and postprandial states, and the power ratios between both before and after ingestion of omeprazole. In addition, administrated omeprazole did not show any significant differences in the gastric emptying parameters such as the half emptying time. We conclude that administration of omeprazole did not affect gastric motility but improved gastric myoelectrical activity. These effects of omeprazole may be one of the mechanisms involved in its efficacy in relieving dyspeptic symptoms in FD patients.

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In isolated longitudinal muscle tissues of the guinea-pig stomach antrum, recording electrical responses from smooth muscle cells revealed a periodical generation of follower potentials with variable durations. The I-D relationship, made by plotting the duration as a function of the interval before generating follower potential, was linear. Experiments were carried out to investigate the effects of chemicals which had been known to modulate the release of Ca²⁺ from the internal stores (2-aminoethoxy-diphenyl-borate, cyclopiazonic acid, caffeine), inhibit mitochondrial metabolic activity (m-chlorophenyl hydrazone, 2-deoxy-D-glucose, potassium cyanide, rotenone), inhibit ATP-sensitive K-channels distributed in mitochondria (glibenclamide, 5-hydroxydecanoic acid) and inhibit the activity of proteinkinase C (chelerythrine), on the I-D relationship of follower potentials. The effects of depolarization on follower potentials were assessed by stimulating tissues with high potassium solution. Experiments were carried out mainly in the presence of nifedipine which minimized the movements of muscles with no modulation of follower potentials. Cycropiazonic acid and caffeine reduced the slope of I-D relationship, with associated reduction of the duration and frequency of follower potentials. 2-Aminoethoxydiphenyl borate reduced the duration and amplitude and increased the frequency of follower potentials, with depolarization of the membrane, and the effects were simulated by high potassium solution. m-Chlorophenyl hydrazone, potassium cyanide, 2-deoxy-D-glucose, rotenone, 5-hydroxydecanoic acid and glibenclamide reduced the slope of I-D relationship, with associated reduction of the frequency of follower potentials. Chelerythrine did not modulate the slope of I-D relationship, with reduced frequency of follower potentials. It seemed likely that the amount of Ca²⁺ released from the internal stores and also mitochondrial function had causal relationship to the duration of pacemaker potentials, suggesting that internal Ca-stores and mitochondria are taking the central role for determining the duration of the pacemaker activity. Proteinkinase C did not seem to participate to the function of mitochondria and internal Ca²⁺ stores.

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Interstitial cells of Cajal (ICC) generate electrical rhythmicity and transduce neural signals in the gastrointestinal musculature. ICC express the proto-oncogene c-kit, a receptor tyrosine kinase, and are identified morphologically by c-Kit immunoreactivity. The c-kit gene is allelic with the murine white-spotting locus W, and mutations of c-kit are known as W mutations. W mutations affect various developmental aspects of hematopoietic cells, germ cells, melanocytes, mast cells and ICC. We examined W^jic/W^jic mutant mice that have a mutation in the tyrosine kinase domain resulting in severe loss of protein function. W^jic/W^jic homozygotes exhibited white coats and black eyes. The gross morphology of the gastrointestinal tract showed no abnormality in mutant mice other than a forestomach papilloma. In the stomach, intramuscular ICC (ICC-IM) were missing, and myenteric ICC (ICC-MY) were reduced in number. In the small intestine, the number of ICC-MY was severely reduced; however there was a normal distribution of deep muscular plexus ICC (ICC-DMP). In the cecum, the numbers of ICC-IM and ICC-MY were severely depleted. ICC-IM were almost entirely absent in the colon, whereas ICC-MY loss was restricted to the distal colon. Patterns of ICC deficiency were generally similar between W^jic/W^jic mice and W/W^v mutants, which lack a specific type of ICC. The enteric nervous system of the mutant mice appeared normal. From these findings, we conclude that W^jic/W^jic mice represent a distinct, novel genotype resulting in a lack of a specific type of ICC in the gastrointestinal musculature.

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