Effects of pH and inorganic phosphate on force production in alpha‐toxin‐permeabilized isolated rat uterine smooth muscle.

Crichton, C. A.; Taggart, Michael J.; Wray, Susan; Smith, Godfrey L.

doi:10.1113/jphysiol.1993.sp019697

Cited by 58 publications

(56 citation statements)

References 25 publications

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“…We have shown Ca2+-activated force development of a-toxin-permeabilized myometrium to be attenuated by increasing [Pi] (Crichton et al 1993) in agreement with studies on other permeabilized smooth muscles (Gagelmann & Guth, 1987;Osterman & Arner, 1995). In guinea-pig taenia coli, raised [Pi] does not alter MLC20 phosphorylation (Gagelmann & Guth, 1987) and inhibits force of maximally thiophosphorylated fibres (Osterman & Arner, 1995 [Pi] on maximum Ca2+-activated force in permeabilized prep-arations (approximately 20 % in the studies of Crichton et al 1993 andOsterman &Arner, 1995 …”

Section: Mlc20 Phosphorylation During Inhibition Of Oxidative Phosphosupporting

confidence: 72%

“…Previous studies in our laboratory have shown that an intracellular acidification per se, induced by the use of weak acids or withdrawal of weak bases, can inhibit spontaneous myometrial contractions (Taggart & Wray, 1995). However, cyanideinduced reductions in force were found to be poorly correlated with changes in intracellular pH (pHi) (Taggart & Wray, 1995) and it was suggested that alterations in [Ca2+]i may underlie the changes in force with mitochondrial inhibition (Crichton, Taggart, Wray & Smith, 1993). Smooth muscle has been suggested to compartmentalize ATP production and utilization, with oxidative phosphorylation associated with mechanical output and (aerobic) glycolysis with regulation of membrane-associated ionic pumps (Paul, 1989 (Huang, Chowdhury, Kobayashi & Tomita, 1993;Lydrup, Sward & Hellstrand, 1994;Aalkjaer & Lombard, 1995 (Taggart, Menice, Wray & Morgan, 1996 b).…”

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confidence: 99%

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Effect of metabolic inhibition on intracellular Ca2+, phosphorylation of myosin regulatory light chain and force in rat smooth muscle.

Taggart

Menice

Morgan

et al. 1997

The Journal of Physiology

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Section: Mlc20 Phosphorylation During Inhibition Of Oxidative Phosphosupporting

confidence: 72%

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confidence: 99%

Effect of metabolic inhibition on intracellular Ca2+, phosphorylation of myosin regulatory light chain and force in rat smooth muscle.

Taggart

Menice

Morgan

et al. 1997

The Journal of Physiology

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“…At suprabasal, but sub-maximal activating Ca 2+ (pCa 6.7) [18] carbachol evoked a gradual but sustained contraction (Fig. 4A) and this carbachol-induced contraction was significantly inhibited by treatment of single uterine smooth muscle cells with 1 µM Y-27632 (Fig.…”

Section: Resultsmentioning

confidence: 99%

Inhibition of Rho-Associated Kinase Reduces MLC20 Phosphorylation and Contractility of Intact Myometrium and Attenuates Agonist-Induced Ca2+ Sensitization of Force of Permeabilized Rat Myometrium.

You

Hwang

et al. 2003

The Journal of Veterinary Medical Science

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ABSTRACT. The role of rhoA/rho-associated kinase (ROK) signaling pathways in agonist-induced contraction of the rat myometrium was investigated. We measured the [Ca 2+ ] i -force relationship, phosphorylation of myosin regulatory light chains (MLC 20 /calmodulin-dependent enzyme myosin light chain kinase and subsequent phosphorylation of the regulatory myosin light chains (MLC 20 ) [2,3]. This increased phosphorylation of MLC 20 enhances actomyosin ATPase activity and uterine force production. Smooth muscle relaxation is preceded by dephosphorylation of MLC 20 by myosin light chain phosphatase (MLCP) [4]. In addition, it has been shown that an increase in the Ca 2+ -sensitivity of the smooth muscle myofilaments contributes to the contraction induced by Ca 2+ -mobilizing agonists [1,5,6]. Recent studies in other smooth muscles have indicated that both rhoA and rhoA-associated kinase (ROK) are involved in this mechanism [7]. ROK is able to regulate the phosphorylation of MLC 20 by the inactivation of myosin light chain phosphatase (MLCP) through the phosphorylation of myosin binding subunit [8].The spontaneous contractions of the myometrium are augmented by a variety of uterotonic agents playing an important role at parturition. These agonists have been reported to increase myometrial contraction, not only by increasing [Ca 2+ ] i , but also by increasing the Ca 2+ sensitivity of myometrial force production through a receptor-coupled, G-protein-mediated mechanism [5,9] that has been suggested, in part at least, to be mediated via activation of ROK [6,10]. Interestingly, in myometria from both rat and humans the mRNA expressions of rhoA and ROK in the pregnant myometrium were increased in comparison to those in the non-pregnant myometrium [11,12]. Our preliminary data has suggested that agonist-induced Ca 2+ -sensitization of force of single permeabilized uterine cells can be attenuated by inhibition of ROK [10]. We have also previously demonstrated in single isolated myometrial cells that rhoA and ROKα translocate from the cytosol to the membrane after carbachol stimulation [13] supportive of the hypothesis that membranous relocalization of rhoA/ROK is necessary for agonist-induced Ca 2+ -sensitization to occur [7,10,13]. Although the above reports are suggestive of an involvement of rhoA and/or ROK in the Ca 2+ sensitization phenomenon, the extent of the putative role of rhoA and ROK in the contractile regulation of pregnant rat myometrium has not been fully elucidated. Therefore, in this study we have further examined the role of ROK-mediated pathways in regulating myometrial contractile function. This has involved comparing the effects of ROK inhibition with Y-27632 on (i) the relationships between [Ca 2+ ] i and force and MLC 20 phosphorylation and force in intact myometrial tissue and (ii) the agonist-induced Ca 2+ sensitivity of contraction in single permeabilized cells.

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“…Although the rise in Pi is considerable, from around 0-8 to 1-6 mm, this is not considered to be the cause of the contractile depression observed, since (i) its time course does not correspond (as shown in the bottom part of Fig. 4, when force has recovered to control levels, Pi is still elevated (128 %) and shows a much slower recovery time), and (ii) in vivo studies of permeabilized myometrium have shown that the levels of Pi found in this study, during occlusion, would have very little effect on Ca2"-activated force, and certainly would not abolish force (Crichton et al 1993). The fall in [ATP] from 1-8 to 1P4 mm likewise would not be expected to have much effect on contraction.…”

Section: Nmr Spectramentioning

confidence: 98%

“…ATP and phosphocreatine (PCr) have been shown to fall and inorganic phosphate (Pi) rise (Wray, 1990). A rise in [Pi] can depress contraction in permeabilized myometrial preparations (Crichton, Taggart, Wray & Smith, 1993). There is also evidence that K+ permeability is increased, which will make the surface membrane more difficult to excite and thus lead to a failure of contraction (Heaton, Wray & Eisner, 1993).…”

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confidence: 99%

An in vivo study of the effects of ischaemia on uterine contraction, intracellular pH and metabolites in the rat.

Harrison

Larcombe-McDouall

Earley

et al. 1994

The Journal of Physiology

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1. There are no data concerning the functional or metabolic effects of hypoxia in vivo in smooth muscle. We have therefore used 3"P-NMR spectroscopy and intra-uterine pressure measurements to examine simultaneously, in vivo, the effect of ischaemia on uterine metabolites, intracellular pH (pHi) and force.2. A 1-2 cm portion of uterus from day 1 postpartum anaesthetized rats was exteriorized and an NMR surface coil placed on it. A balloon catheter in the uterine lumen recorded intra-uterine pressure changes from the same area. Reversible occluders were placed around the uterine artery. 3. Occlusion produced a decrease and then abolition of contractions, within 10 min. In four of five animals contraction was abolished within 2 min. Upon reperfusion force was rapidly restored (1 min), in all preparations. The mean level of force was significantly above control (pre-occlusion) 20-30 min after reperfusion. 4. The NMR data showed a significant fall in [ATP] (28 %) and [phosphocreatine] (34 %) during occlusion. Inorganic phosphate doubled in concentration during this period. Metabolites recovered slowly upon reperfusion, taking 20-30 min to return to preocclusion levels.5. The mean pHi fell from 7-32 to 7 00 upon occlusion and was rapidly reversed upon reperfusion. The changes in pHi closely correlated with the changes in uterine force. Decreases of pHi of a similar magnitude in vitro have previously been shown to abolish contractions; thus it is suggested that during ischaemia in vivo the depression of contraction is caused by the large fall in pHi.The effect of hypoxia or ischaemia in vivo on smooth muscle function, metabolites and intracellular pH (pH1) is unknown. Given the important roles played by smooth muscle cells within the body and the fact that tissue blood flow and oxygenation may well alter under different physiological conditions, it is important that such information be obtained. We have therefore investigated the effects of ischaemia on uterine smooth muscle in vivo.

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Effects of pH and inorganic phosphate on force production in alpha‐toxin‐permeabilized isolated rat uterine smooth muscle.

Cited by 58 publications

References 25 publications

Effect of metabolic inhibition on intracellular Ca2+, phosphorylation of myosin regulatory light chain and force in rat smooth muscle.

Effect of metabolic inhibition on intracellular Ca2+, phosphorylation of myosin regulatory light chain and force in rat smooth muscle.

Inhibition of Rho-Associated Kinase Reduces MLC20 Phosphorylation and Contractility of Intact Myometrium and Attenuates Agonist-Induced Ca2+ Sensitization of Force of Permeabilized Rat Myometrium.

An in vivo study of the effects of ischaemia on uterine contraction, intracellular pH and metabolites in the rat.

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