Blebbistatin, a potent inhibitor of myosin II, is known to suppress smooth muscle contraction without affecting myosin light chain phosphorylation level. In order to clarify the regulatory mechanisms of blebbistatin on phasic and tonic smooth muscles in detail, we examined the effects of blebbistatin on relaxation process by Ca2+ removal after Ca2+-induced contraction of β-escin skinned (cell membrane permeabilized) trachea and taenia cecum preparations from guinea pigs. Blebbistatin significantly suppressed the force during relaxation both in skinned trachea and taenia cecum. The data fitting analysis of the relaxation processes indicates that blebbistatin accelerates slow (latch-like) bridge dissociation.
The c-Kit receptor tyrosine kinase regulates the development and differentiation of several progenitor cells. In the gastrointestinal (GI) tract, the c-Kit regulates the development of the interstitial cells of Cajal (ICC) that are responsible for motility regulation of the GI musculature. W-sash (Wsh) is an inversion mutation upstream of the c-kit promoter region that affects a key regulatory element, resulting in cell-type-specific altered gene expression, leading to a decrease in the number of mast cells, melanocytes, and ICC. We extensively examined the GI tract of Wsh/Wsh mice using immunohistochemistry and electron microscopy. Although the musculature of the Wsh/Wsh mice did not show any c-Kit immunoreactivity, we detected intensive immunoreactivity for transmembrane member 16A (TMEM16A, anoctamin-1), another ICC marker. TMEM16A immunopositive cells were observed as ICC-MY in the gastric corpus-antrum and the large intestine, ICC-DMP in the small intestine, and ICC-SM in the colon. Electron microscopic analysis revealed these cells as ICC from their ultrastructural features, such as numerous mitochondria and caveolae, and their close contact with nerve terminals. In the developmental period, we examined 14.5 and 18.5 day embryos but did not observe c-Kit immunoreactivity in the Wsh/Wsh small intestine. From this study, ICC subtypes developed and maturated structurally without c-Kit expression. Wsh/Wsh mice are a new model to investigate the effects of c-Kit and unknown signaling on ICC development and function.
Spontaneous rhythmic constrictions known as vasomotion are developed in several microvascular beds in vivo. Vasomotion in arterioles is considered to facilitate blood flow, while venular vasomotion would facilitate tissue metabolite drainage. Mechanisms underlying vasomotion periodically generate synchronous Ca2+ transients in vascular smooth muscle cells (VSMCs). In visceral organs, mural cells (pericytes and VSMCs) in arterioles, capillaries and venules exhibit synchronous spontaneous Ca2+ transients. Since sympathetic regulation is rather limited in the intra-organ microvessels, spontaneous activity of mural cells may play an essential role in maintaining tissue perfusion. Synchronous spontaneous Ca2+ transients in precapillary arterioles (PCAs)/capillaries appear to propagate to upstream arterioles to drive their vasomotion, while venules develop their own synchronous Ca2+ transients and associated vasomotion. Spontaneous Ca2+ transients of mural cells primarily arise from IP3 and/or ryanodine receptor-mediated Ca2+ release from sarcoendoplasmic reticulum (SR/ER) Ca2+ stores. The resultant opening of Ca2+-activated Cl- channels (CaCCs) causes a membrane depolarisation that triggers Ca2+ influx via T-type and/or L-type voltage-dependent Ca2+ channels (VDCCs). Mural cells are electrically coupled with each other via gap junctions, and thus allow the sequential spread of CaCC or VDCC-dependent depolarisations to develop the synchrony of Ca2+ transients within their network. Importantly, the synchrony of spontaneous Ca2+ transients also requires a certain range of the resting membrane potential that is maintained by the opening of Kv7 voltage-dependent K+ (Kv7) and inward rectifier K+ (Kir) channels. Thus, a depolarised membrane would evoke asynchronous, ‘premature’ spontaneous Ca2+ transients, while a hyperpolarised membrane prevents any spontaneous activity.
Rubratoxin A, a potent inhibitor of PP2A, is known to suppress smooth muscle contraction. The inhibitory role of PP2A in smooth muscle contraction is still unclear. In order to clarify the regulatory mechanisms of PP2A on vascular smooth muscle contractility, we examined the effects of rubratoxin A on the Ca2+-induced contraction of β-escin skinned carotid artery preparations from guinea pigs. Rubratoxin A at 1 µM and 10 µM significantly inhibited skinned carotid artery contraction at any Ca2+ concentration. The data fitting to the Hill equation in [Ca2+]-contraction relationship indicated that rubratoxin A decreased Fmax-Ca2+ and increased [Ca2+]50, indices of Ca2+ sensitivity for the force and myosin-actin interaction, respectively. These results suggest that PP2A inhibition causes downregulation of the myosin light chain phosphorylation and direct interference with myosin-actin interaction.
Prostaglandin D2 (PGD2), one of the key lipid mediators of allergic airway inflammation, is increased in the airways of asthmatics. However, the role of PGD2 in the pathogenesis of asthma is not fully understood. In the present study, effects of PGD2 on smooth muscle contractility of the airways were determined to elucidate its role in the development of airway hyperresponsiveness (AHR). In a murine model of allergic asthma, antigen challenge to the sensitized animals caused a sustained increase in PGD2 levels in bronchoalveolar lavage (BAL) fluids, indicating that smooth muscle cells of the airways are continually exposed to PGD2 after the antigen exposure. In bronchial smooth muscles (BSMs) isolated from naive mice, a prolonged incubation with PGD2 (10−5 M, for 24 h) induced an augmentation of contraction induced by acetylcholine (ACh): the ACh concentration-response curve was significantly shifted upward by the 24-h incubation with PGD2. Application of PGD2 caused phosphorylation of ERK1/2 and p38 in cultured BSM cells: both of the PGD2-induced events were abolished by laropiprant (a DP1 receptor antagonist) but not by fevipiprant (a DP2 receptor antagonist). In addition, the BSM hyperresponsiveness to ACh induced by the 24-h incubation with PGD2 was significantly inhibited by co-incubation with SB203580 (a p38 inhibitor), whereas U0126 (a ERK1/2 inhibitor) had no effect on it. These findings suggest that prolonged exposure to PGD2 causes the BSM hyperresponsiveness via the DP1 receptor-mediated activation of p38. A sustained increase in PGD2 in the airways might be a cause of the AHR in allergic asthmatics.
Central nervous control of micturition and urine storage
公開日: 2005/07/09 | 41 巻 p. 117-132
Kimio Sugaya, Saori Nishijima, Minoru Miyazato, Yoshihide Ogawa
Views: 155
下部食道括約筋運動に対する迷走神経因子に関する実験的および臨床的研究
公開日: 2010/07/21 | 30 巻 p. 97-110
阿部 貞信
Views: 75
緑内障および内眼筋の神経性液性調節
公開日: 2010/07/21 | 32 巻 p. 175-194
鈴木 亮
Views: 53
New Aspects of Gastric Adaptive Relaxation, Reflex after Food Intake for More Food: Involvement of Capsaicin-sensitive Sensory Nerves and Nitric Oxide
公開日: 2010/07/21 | 33 巻 p. 81-88
Tetsuo ARAKAWA, Hironori UNO, Takashi FUKUDA, Kazuhide HIGUCHI, Kenzo KOBAYASHI, Tetsuo KUROKI
Views: 40
平滑筋組織におけるNANC (非アドレナリン非コリン) 性神経支配
公開日: 2010/07/21 | 31 巻 p. 67-78
伊東 祐之, 坂井 二郎, 井本 昭彦, Kate E. CREED
Views: 37