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Kramer PR, Guerrero G, Krishnamurthy R, Mitchell PJ, Wray S. Ectopic expression of luteinizing hormone-releasing hormone and peripherin in the respiratory epithelium of mice lacking transcription factor AP-2alpha. Mech Dev 2000; 94:79-94. [PMID: 10842061 DOI: 10.1016/s0925-4773(00)00316-6] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
The vertebrate transcription factor activator protein-2 (AP-2alpha) is involved in craniofacial morphogenesis. In the nasal placode AP-2alpha expression delineates presumptive respiratory epithelia from olfactory epithelia, with AP-2alpha expression restricted to the anterior region of the respiratory epithelium (absent from the olfactory epithelium) at later stages. To address the role AP-2alpha plays in differentiation of cell groups in the nasal placode, the spatiotemporal expression pattern of four markers normally associated with olfactory epithelial structures was analyzed in mice lacking AP-2alpha. These markers were the intermediate filament protein peripherin, the neuropeptide luteinizing hormone-releasing hormone (LHRH), the neural cell adhesion molecule (NCAM) and the olfactory transcription factor Olf-1. Development of cells expressing these markers was similar in both genotypes until embryonic day 12.5 (E12.5), indicating that the main olfactory epithelium and olfactory pit formation was normal. At E13.5 in mutant mice, ectopic LHRH neurons and peripherin axons were detected in respiratory epithelial areas, areas devoid of Olf-1 and NCAM staining. Over the next few days, an increase in total nasal LHRH neurons occurred. The increase in nasal LHRH neurons could be accounted for by LHRH neurons arising and migrating out of respiratory epithelial regions on peripherin-positive fibers. These results indicate that AP-2alpha is not essential for the separation of the olfactory and respiratory epithelium from the nasal placode and is consistent with AP-2alpha preventing recapitulation of developmental programs within the respiratory epithelium that lead to expression of LHRH and peripherin phenotypes.
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Longbottom ER, Luckas MJ, Kupittayanant S, Badrick E, Shmigol T, Wray S. The effects of inhibiting myosin light chain kinase on contraction and calcium signalling in human and rat myometrium. Pflugers Arch 2000; 440:315-21. [PMID: 10898533 DOI: 10.1007/s004240000305] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
The effect of inhibiting myosin light chain kinase on contractions of human and rat myometrium has been investigated, to determine whether force can be produced independently of myosin phosphorylation. Two inhibitors were used, wortmannin and ML-9, and their effects on spontaneous, high-K-depolarization-induced and oxytocin-induced force studied. Both inhibitors reduced and then abolished uterine force, irrespective of how it was produced; this was the case for both human and rat myometrium, and pregnant and non-pregnant tissue. The effects of wortmannin on intracellular [Ca2+] and inward Ca2+ current were examined. The data showed that the reduction in force produced by wortmannin occurs without a reduction of either the Ca2+ current or [Ca2+]. It is concluded that, under normal physiological conditions, myosin light chain kinase phosphorylation of myosin is essential for uterine force production and that there is little or no role for alternative force-producing pathways.
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Kramer PR, Krishnamurthy R, Mitchell PJ, Wray S. Transcription factor activator protein-2 is required for continued luteinizing hormone-releasing hormone expression in the forebrain of developing mice. Endocrinology 2000; 141:1823-38. [PMID: 10803593 DOI: 10.1210/endo.141.5.7452] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
LHRH is the neuropeptide responsible for reproductive function. Prenatally, LHRH expression begins when neurons are in the olfactory pit and continues as these cells migrate into the brain. Thus, LHRH neurons maintain neuropeptide expression through very distinct environments. The regulatory interactions that control onset and continued expression of the LHRH phenotype are unknown. To begin to address this question primary LHRH neurons were removed from nasal explants at different ages. A complementary DNA (cDNA) subtraction screen was performed comparing a 3.5-days in vitro LHRH neuron [approximately embryonic day 15 (E15) in vivo] to two 10.5-days in vitro LHRH neurons (approximately postnatal day 1 in vivo). The transcription factor activator protein-2 (AP-2alpha) was differentially expressed and was present in the developmentally younger LHRH neuron. In vivo analysis revealed that LHRH neurons expressed AP-2 as they migrated across the cribriform plate and into the forebrain beginning on E13.5, but that coexpression of LHRH and AP-2 was no longer detected in postnatal day 1 animals. This suggested a regulatory role for AP-2 in LHRH neurons. Analysis of animals lacking AP-2alpha revealed a dramatic decrease in forebrain LHRH neurons between E13.5 and E14.5, correlating with normal onset of AP-2 expression in LHRH neurons as they entered the central nervous system. Nasal cells robustly expressing LHRH were still present on E 14.5. The continued presence of forebrain LHRH cells is proposed based on a second marker, galanin, and lack of increased apoptotic/necrotic cells in this region. A decrease in LHRH messenger RNA in forebrain neurons indicates regulation of LHRH occurred at the transcriptional or posttranscriptional level in mutant animals. These results indicate a developmentally restricted involvement of the transcription factor AP-2 in LHRH expression once the LHRH neurons have migrated into the forebrain, but before establishment of an adult-like distribution.
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Abstract
Ca(2+) and H(+) ions can profoundly alter vascular tone. In many physiological and pathological processes, changes in the concentration of both ions occur. Thus, to understand the processes and mechanisms that modify force, it is necessary to understand what changes occur in these ions and, importantly, how they interact with each other. In this minireview, we highlight the quantitatively important mechanisms involved in the contractile responses of vascular tissues to pH change and discuss the cellular and molecular reasons underlying these responses.
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Burdyga TV, Wray S. The relationship between the action potential, intracellular calcium and force in intact phasic, guinea-pig uretic smooth muscle. J Physiol 1999; 520 Pt 3:867-83. [PMID: 10545150 PMCID: PMC2269613 DOI: 10.1111/j.1469-7793.1999.00867.x] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/1999] [Accepted: 08/10/1999] [Indexed: 11/29/2022] Open
Abstract
1. We investigated the relationship between the action potential, Ca2+ and phasic force in intact guinea-pig ureter, following physiological activation. 2. The action potential elicited a Ca2+ transient consisting of three components: a fast increment, associated with the first action potential spike, a slower increment, associated with subsequent spikes and the initial part of the plateau component, and a steady-state phase associated with the plateau. 3. Prolongation of the plateau, by agonists, prolonged the third component of the Ca2+ transient and increased force amplitude and duration. 4. The force-Ca2+ relationship during phasic contractions showed hysteresis; more force was produced as Ca2+ declined than when it rose. Paired pulse stimuli suggested that the delay between Ca2+ and force was not due to mechanical properties. Wortmannin, which has been shown to selectively inhibit force and myosin light chain (MLC) phosphorylation in the guinea-pig ureter, did not affect electrical activity or Ca2+ but significantly increased the delay, suggesting that myosin phosphorylation is a major contributor to it. 5. Prolongation of the duration of the [Ca2+]i transient, at unchanged amplitude, increased force. The rise of [Ca2+]i did not limit the rate of contraction. Slowing of the rate of [Ca2+]i rise abolished the hysteresis between Ca2+ and force. 6. Cooling reduced force, increased the delay and hysteresis between Ca2+ and force, but did not affect the rate of rise of Ca2+. The reduction in force could be compensated, by increasing the duration of the Ca2+ transient. 7. We suggest that in vivo, steady-state force-Ca2+ relationships are not applicable in phasic smooth muscles. Furthermore, agonists increase force mainly by prolonging the action potential, which increases the duration of the [Ca2+] signal.
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Shmigol AV, Eisner DA, Wray S. The role of the sarcoplasmic reticulum as a Ca2+ sink in rat uterine smooth muscle cells. J Physiol 1999; 520 Pt 1:153-63. [PMID: 10517808 PMCID: PMC2269575 DOI: 10.1111/j.1469-7793.1999.00153.x] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
1. The mechanisms responsible for removing calcium ions from the cytoplasm were investigated in single rat uterine myocytes using indo-1. 2. Trains of depolarizing voltage-clamp pulses increased [Ca2+]i. The rate of decay of [Ca2+]i was slowed by inhibition of the sarcoplasmic reticulum (SR) Ca2+-ATPase with cyclopiazonic acid (CPA). However, if the sarcolemmal Na+-Ca2+ exchanger and Ca2+-ATPase were inhibited then recovery of [Ca2+]i was abolished showing that the SR Ca2+-ATPase alone cannot produce decay of [Ca2+]i. 3. In another series of experiments, Ca2+ release from the SR was induced with carbachol in a Ca2+-free solution. Under these conditions responses to repeated applications of carbachol could be obtained. In the presence of CPA, however, only the first application was effective. This suggests that the SR Ca2+-ATPase sequesters a significant amount of Ca2+ into the SR. 4. CPA slowed the rate of decay of [Ca2+]i following carbachol addition by > 50 %. Again, however, after a brief transient fall, decay was abolished when the Na+-Ca2+ exchanger and sarcolemmal Ca2+-ATPase were inhibited. 5. These data show that, although the SR Ca2+-ATPase contributes to the decay of [Ca2+]i, it cannot function effectively in the absence of Ca2+ removal from the cell. These data are discussed in the context of the superficial buffer barrier model in which Ca2+ is taken up into the SR and then released very close to sarcolemmal Ca2+ extrusion sites, i.e. the SR acting in series with the surface membrane extrusion mechanisms. We also suggest that the amount of filling of the SR influences the rate of Ca2+ removal.
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Naderali EK, Wray S. Modulation of force induced by pH in the guinea-pig uterus examined at two stages of the oestrous cycle. JOURNAL OF REPRODUCTION AND FERTILITY 1999; 117:153-7. [PMID: 10645256 DOI: 10.1530/jrf.0.1170153] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Changes in pH have a marked influence on uterine contractility. Changes in uterine pH occur during pregnancy and labour, when marked endocrine changes are occurring. As hormonal status can also influence contractility, this study investigated whether pH-induced modulation of uterine force in influenced by hormonal changes. The effects of altering intracellular and extracellular pH on uterine contractions were studied in guinea-pigs on day 7 (high progesterone) and day 15 (low progesterone) of the oestrous cycle. Resting values of pH were significantly more acidic on day 15 compared with day 7, and more force was produced on day 15. Changing external pH produced similar changes in intracellular pH and force on both days. External acidification was associated with a large increase in force. In contrast, intracellular acidification, at constant external pH, reduced force. In conclusion, the stage of the oestrous cycle has a large effect on resting pH in the myometrium but only small effects on the pH-induced modulation of force, and the link between pH and force is complex.
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Larcombe-McDouall J, Buttell N, Harrison N, Wray S. In vivo pH and metabolite changes during a single contraction in rat uterine smooth muscle. J Physiol 1999; 518 ( Pt 3):783-90. [PMID: 10420014 PMCID: PMC2269472 DOI: 10.1111/j.1469-7793.1999.0783p.x] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/1999] [Accepted: 06/15/1999] [Indexed: 11/30/2022] Open
Abstract
1. We have used 31P NMR spectroscopy to measure metabolites and pHi at three periods during a phasic contraction of the uterus, in vivo, to determine whether they change as a consequence of contraction. The regular uterine contractions were recorded via a balloon catheter in the uterine lumen. Each phasic contraction was divided into three parts: the period between contractions (rest), the development of force (up) and the relaxation of force (down). The NMR data were summed separately from each of these three periods over 20-40 successive contractions. 2. Significant changes in ATP, phosphocreatine (PCr) and inorganic phosphate (Pi) occurred during the contraction. [ATP] fell from 2.0 to 1.6 mM and [PCr] from 2.6 to 2.0 mM during the up period, while [Pi] increased from 2.2 to 2.8 mM. Recovery of ATP and PCr occurred during the relaxation part of the contraction, whereas Pi did not fully recover until the contraction was complete. 3. Significant acidification from pH 7.28 +/- 0.02 at rest to 7.16 +/- 0.02, occurred with contraction. This acidification is greater than that previously reported for in vitro uterine preparations. Measurements of uterine blood flow show that it decreased with contraction. Therefore, ischaemia, in addition to the metabolic consequences of contraction, may account for the larger acidification observed in vivo. 4. Lowering pHi in an in vitro uterine preparation by a similar level to that found in vivo produced a significant reduction of the phasic contractions. Thus we propose that these changes, especially the fall in pHi during force development, feed back negatively on the contraction to limit its strength, and may help prevent uterine ischaemia and fetal hypoxia during labour.
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Luckas MJ, Taggart MJ, Wray S. Intracellular calcium stores and agonist-induced contractions in isolated human myometrium. Am J Obstet Gynecol 1999; 181:468-76. [PMID: 10454702 DOI: 10.1016/s0002-9378(99)70580-6] [Citation(s) in RCA: 66] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
OBJECTIVE We hypothesized that the release of calcium from intracellular stores contributes to the contractions produced by the agonists oxytocin, carbachol, and prostaglandin F(2 )(alpha ) in human myometrium. STUDY DESIGN Strips of myometrium were obtained at cesarean section and hysterectomy. The strips were loaded with the calcium-sensitive dye Indo-1 to enable simultaneous measurement of tension and intracellular calcium levels. Agonist-induced responses in the presence and absence of extracellular calcium were studied. RESULTS Strips of myometrium were obtained from 48 women not in labor undergoing cesarean section and 6 women not pregnant undergoing hysterectomy. An increase in intracellular calcium level after agonist stimulation invariably preceded an increase in tension. Intracellular calcium level returned to baseline before myometrial relaxation. Oxytocin, carbachol, and prostaglandin F(2)(alpha) all gave both force and intracellular calcium responses in the absence of extracellular calcium, although both these responses were only 26% to 40% of the maximal response when extracellular calcium was present. CONCLUSIONS Release of calcium from internal stores induced by oxytocin, carbachol, and prostaglandin F(2)(alpha) may contribute to agonist-induced myometrial force production.
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Burdyga TV, Wray S. The effect of cyclopiazonic acid on excitation-contraction coupling in guinea-pig ureteric smooth muscle: role of the sarcoplasmic reticulum. J Physiol 1999; 517 ( Pt 3):855-65. [PMID: 10358124 PMCID: PMC2269382 DOI: 10.1111/j.1469-7793.1999.0855s.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
1. We have investigated the effect of cyclopiazonic acid (CPA), an inhibitor of the sarcoplasmic reticulum (SR) Ca2+-ATPase on excitation-contraction (EC) coupling in guinea-pig ureter, by measuring membrane currents, action potentials, intracellular [Ca2+] and force. 2. CPA (20 micrometers) significantly enhanced the amplitude and duration of phasic contractions of ureteric smooth muscle associated with action potentials. This was accompanied by an increase in the duration of the intracellular Ca2+ transient in intact tissue and single cells but not their amplitude. However, CPA also slowed the rate of rise, and fall, of the force 1|1|Phiand1Phi Ca2+ transients. 3. Membrane potential recordings showed that CPA produced a small depolarization and a large increase in the duration of the plateau phase of the action potential. 4. Patch-clamp studies showed marked inhibition of outward potassium current in the presence of CPA and an inhibition of spontaneous transient outward currents (STOCs). CPA had no effect on inward Ca2+ current. 5. These data suggest that the SR plays a major role in modulating the excitability of the ureter, particularly via curtailing the action potential duration. This in turn will shorten the Ca2+ transient and decrease force. This negative action on developed force predominates over any small role it may play in initiating force in the guinea-pig ureter.
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61
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Langbein J, Hutchings MR, Harris S, Stoate C, Tapper SC, Wray S. Techniques for assessing the abundance of Brown Hares Lepus europaeus. Mamm Rev 1999. [DOI: 10.1046/j.1365-2907.1999.00040.x] [Citation(s) in RCA: 79] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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62
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Wray S. A barter system. NURSING TIMES 1999; 95:45. [PMID: 10373959] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 04/13/2023]
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63
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Maurer JA, Wray S. Luteinizing hormone-releasing hormone quantified in tissues and slice explant cultures of postnatal rat hypothalami. Endocrinology 1999; 140:791-9. [PMID: 9927307 DOI: 10.1210/endo.140.2.6534] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
LH-releasing hormone (LHRH) peptide from postnatal rat preoptic area (POA)/hypothalamic tissues in vivo and slice explant cultures maintained in vitro was quantitated using an enzyme-linked immunosorbant assay. Moreover, messenger RNA (mRNA) copy number was calculated in LHRH neurons maintained in culture using in situ hybridization histochemistry with autoradiographic film analysis. POA/hypothalami from postnatal day 5-6 pups averaged 1250 pg of LHRH, with approximately 28% of peptide residing within rostral tissues where most LHRH perikarya reside. Explant cultures maintained 18 days in vitro contained 30.4-92.0 pg/slice with a whole animal total of 244.8 pg. Considering cell numbers in vivo and in vitro, LHRH neurons in whole animal produce 1.0 pg of LHRH/cell, whereas those in culture average 2.0 pg/cell. Furthermore, LHRH mRNA copies/cell in organotypic culture was estimated conservatively at 1410 copies/cell, a relatively high number. This work shows that, compared with whole animal, cultures have substantial LHRH stores, indicating maturation of synthetic activity and/or formation of new terminals in vitro. High LHRH mRNA copy number also suggests a high rate of peptide biosynthesis. Our analysis, demonstrating the dynamic potential of LHRH neurons, suggests that subtle changes in LHRH mRNA expression in all cells or a subpopulation can dramatically alter the LHRH system biosynthetic capacity.
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64
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Shmigol A, Eisner DA, Wray S. Carboxyeosin decreases the rate of decay of the [Ca2+]i transient in uterine smooth muscle cells isolated from pregnant rats. Pflugers Arch 1998; 437:158-60. [PMID: 9817801 DOI: 10.1007/s004240050761] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
In myometrial smooth muscle cells the rate of decline of intracellular calcium ([Ca2+]i) is determined by Ca2+ extrusion from the cell and uptake into intracellular stores. The relative quantitative contribution of these processes however, has not been established. We therefore examined the effect of the sarcolemmal Ca2+ pump inhibitor, carboxyeosin, on the rate of the [Ca2+]i transient decline in myocytes isolated from pregnant rat uterus. Indo-1 was used in conjunction with the whole-cell patch-clamp technique to measure [Ca2+]i simultaneously with transmembrane calcium current (ICa). [Ca2+]i transients were elicited by repetitive membrane depolarization to simulate the natural pattern of uterine electrical activity. The rate of [Ca2+]i removal was calculated from the falling phase of the [Ca2+]i transient. Pre-treatment of the cells with 2 microM carboxyeosin led to a marked decrease in the rate of [Ca2+]i transient decay, suggesting that the sarcolemmal Ca2+ pump is involved in the calcium extrusion process. Removal of the extracellular Na also decreased the rate of [Ca2+]i decay, indicating an important role for the Na+/Ca2+ exchange. When both the sarcolemmal Ca2+ pump and Na+/Ca2+ exchange were inhibited the cell failed to restore [Ca2+]i after the stimulation. Comparison of the rate constants of [Ca2+]i decay in control conditions and after carboxyeosin treatment shows that approximately 30% of [Ca2+]i decay is due to the sarcolemmal calcium pump activity. The remaining 70% can be attributed to the activity of Na+/Ca2+ exchanger and the intracellular calcium stores.
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65
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Burdyga TV, Wray S. The effect of inhibition of myosin light chain kinase by Wortmannin on intracellular [Ca2+], electrical activity and force in phasic smooth muscle. Pflugers Arch 1998; 436:801-3. [PMID: 9716716 DOI: 10.1007/s004240050705] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
To investigate the role of myosin light chain kinase (MLCK) in phasic contractions of intact smooth muscle, we have applied Wortmannin, an MLCK inhibitor, to strips of guinea-pig ureter. Simultaneous measurements of electrical activity, intracellular [Ca2+] ([Ca2+]i) and phasic force showed that Wortmannin (1-4 microM) abolishes force with little or no change in [Ca2+]i and electrical activity. High-K+-induced force production was also abolished by Wortmannin. The effects of Wortmannin were dose dependent - at lower concentrations (100 nM) Wortmannin reduced phasic contractility by 40-50%. It also significantly increased the delay between the Ca2+ peak and force production. These data show that, in phasic smooth muscle, inhibition of MLCK causes contraction to fail, despite normal electrical activity and Ca2+ transients. Our results also indicate that Wortmannin has no secondary effects and that other means of producing force, independent of myosin phosphorylation, are negligible in this tissue. The increased lag between the rise of Ca2+ and force production when MLCK is inhibited was surprising and suggests that post-phosphorylation steps may play a larger role in the delay than was previously considered.
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66
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Shmigol AV, Eisner DA, Wray S. Properties of voltage-activated [Ca2+]i transients in single smooth muscle cells isolated from pregnant rat uterus. J Physiol 1998; 511 ( Pt 3):803-11. [PMID: 9714861 PMCID: PMC2231157 DOI: 10.1111/j.1469-7793.1998.803bg.x] [Citation(s) in RCA: 70] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/1997] [Accepted: 06/02/1998] [Indexed: 11/30/2022] Open
Abstract
1. The intracellular calcium concentration ([Ca2+]i) was measured at 35 degrees C using the fluorescent indicator indo-1 in patch-clamped, single uterine myocytes from pregnant rats to investigate the relationship between depolarization, Ca2+ current (ICa) and [Ca2+]i. 2. Membrane depolarization activated ICa and produced a [Ca2+]i transient. The rapid increase in [Ca2+]i occurred at the same time as the inward ICa. Both ICa and the increase in [Ca2+]i were abolished by nifedipine (10 microM). 3. When the membrane potential was held at -80 mV the threshold depolarization for an increase in [Ca2+]i was about -55 to -50 mV. As the magnitude of the depolarization was increased to about 0 mV there was an increase in the size of both ICa and the increase in [Ca2+]i. As the magnitude of the depolarization was further increased both ICa and the [Ca2+]i increase declined. 4. When the depolarizing pulses were applied at 3 Hz to mimic normal action potentials then the individual [Ca2+]i transients did not fully relax and a tetanic rise of [Ca2+]i was observed. Under these conditions, there was not a simple relationship between the magnitude of the Ca2+ response and Ca2+ entry. When pairs of depolarizing pulses were applied, the increase in [Ca2+]i produced by the second pulse was larger (in relation to the magnitude of the L-type Ca2+ current) than that produced by the first pulse. This facilitation was abolished by both ryanodine and cyclopiazonic acid suggesting a role for release from intracellular stores. 5. We conclude that the L-type Ca2+ current is the major source of Ca2+ ions entering the cell to produce the [Ca2+]i transient on depolarization. The magnitude of the increase in [Ca2+]i may, however, be amplified by Ca2+-induced Ca2+ release.
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67
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Taggart MJ, Wray S. Contribution of sarcoplasmic reticular calcium to smooth muscle contractile activation: gestational dependence in isolated rat uterus. J Physiol 1998; 511 ( Pt 1):133-44. [PMID: 9679169 PMCID: PMC2231104 DOI: 10.1111/j.1469-7793.1998.133bi.x] [Citation(s) in RCA: 80] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/1998] [Accepted: 04/17/1998] [Indexed: 11/27/2022] Open
Abstract
1. The contribution of Ca2+ released from the sarcoplasmic reticulum (SR) to smooth muscle contractile activation remains poorly understood. By simultaneously monitoring cytosolic [Ca2+] ([Ca2+]i) and force in isolated rat uterine smooth muscle, we report the influence of SR Ca2+ release on contractility during conditions (a) of altered SR Ca2+ homeostasis and (b) where the only source of activating Ca2+ was derived from the SR. 2. In myometria of non-pregnant rats, ryanodine (1-50 microM), a modulator of calcium-induced calcium release (CICR), had no effect on the spontaneous [Ca2+]i or force transients. However, depletion of SR Ca2+ by inhibiting the SR Ca2+-ATPase (with cyclopiazonic acid (CPA), 20 microM) resulted in an enhancement of spontaneous [Ca2+]i and force transients. 3. In myometria of pregnant rats, although ryanodine had no effect in 40% of tissues studied it produced a small but significant enhancement of the integrated spontaneous [Ca2+]i and force transient in 60% of cases. The potentiating effects of CPA were enhanced in myometria of pregnant rats compared with non-pregnant rats, often resulting in maintained [Ca2+]i increases and contraction. 4. In zero external Ca2+, agonist-induced SR Ca2+ release resulted in transient increases in [Ca2+]i and force. The magnitude of these agonist-induced [Ca2+]i and force changes were significantly enhanced in myometria of pregnant rats. No evidence for agonist-induced Ca2+-independent force production was observed. 5. These results indicate that CICR plays little role in SR Ca2+ release from the myometrium, and that there are gestational-dependent alterations in the ability of SR Ca2+ mobilization to contribute to contractile activation. The implications of these findings for the co-ordination of myometrial [Ca2+]i signalling and contractility are discussed.
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68
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Bullock AJ, Wray S. Developmental and species differences in the response of the ureter to metabolic inhibition. Pflugers Arch 1998; 436:443-8. [PMID: 9644228 DOI: 10.1007/s004240050655] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
The effect of inhibiting oxidative phosphorylation on electrically stimulated phasic and high-K+ depolarization-induced tonic contractions in ureteric smooth muscle has been investigated. Intracellular [Ca2+] and pH were monitored fluorimetrically with simultaneous tension measurement, in adult and neonatal rat and guinea-pig ureter. Little difference was found in the response of adult or neonatal rat ureters; cyanide abolished phasic contractions and intracellular Ca2+ transients. The contractions of the adult guinea-pig ureter were also reduced by cyanide, but not as much as those of the adult rat. Neonatal guinea-pig was, however, remarkably resistant to the effects of cyanide, with force and Ca2+ transients remaining at control levels after an initial transient dip. These differences between tissues were not apparent when a high K+ concentration was used to depolarize tissues and produce maintained [Ca2+]i and force changes; cyanide reduced force but not [Ca2+]i in all preparations. Intracellular pH decreased in all preparations with inhibition of oxidative phosphorylation, but this did not correlate with changes in contraction. It is concluded that there are both species and developmental differences in the response to metabolic inhibition of the ureter which lead to differing changes in contractile activity.
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69
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Fueshko SM, Key S, Wray S. Luteinizing hormone releasing hormone (LHRH) neurons maintained in nasal explants decrease LHRH messenger ribonucleic acid levels after activation of GABA(A) receptors. Endocrinology 1998; 139:2734-40. [PMID: 9607779 DOI: 10.1210/endo.139.6.6034] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Inhibition of the LHRH system appears to play an important role in preventing precocious activation of the hypothalamic-pituitary-gonadal axis. Evidence points to gamma-aminobutyric acid (GABA) as the major negative regulator of postnatal LHRH neuronal activity. Changes in LHRH messenger RNA (mRNA) levels after alterations of GABAergic activity have been reported in vivo. However, the extent to which GABA acts directly on LHRH neurons to effect LHRH mRNA levels has been difficult to ascertain. The present work evaluates the effect of GABAergic activity, via GABA(A) receptors, on LHRH neuropeptide gene expression in LHRH neurons maintained in olfactory explants generated from E11.5 mouse embryos. These explants maintain large numbers of primary LHRH neurons that migrate from bilateral olfactory pits in a directed manner. Using in situ hybridization histochemistry and single cell analysis, we report dramatic alterations in LHRH mRNA levels. Inhibition of spontaneous synaptic activity by GABA(A) antagonists, bicuculline (10(-5) M) or picrotoxin (10(-4) M), or of electrical activity by tetrodotoxin (TTX, 10(-6) M) significantly increased LHRH mRNA levels. In contrast, LHRH mRNA levels decreased in explants cultured with the GABA(A) receptor agonist, muscimol (10(-4) M), or KCl (50 mM). The observed responses suggest that LHRH neurons possess functional pathways linking GABA(A) receptors to repression of neuropeptide gene expression and indicate that gene expression in embryonic LHRH neurons, outside the CNS, is highly responsive to alterations in neuronal activity.
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Taggart MJ, Wray S. Hypoxia and smooth muscle function: key regulatory events during metabolic stress. J Physiol 1998; 509 ( Pt 2):315-25. [PMID: 9575282 PMCID: PMC2230985 DOI: 10.1111/j.1469-7793.1998.315bn.x] [Citation(s) in RCA: 92] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/1998] [Accepted: 03/31/1998] [Indexed: 11/28/2022] Open
Abstract
Hypoxia rapidly reduces force in many smooth muscles and we review recent data that shed light on the mechanisms involved. As many regulated cellular processes are integrated to co-ordinate smooth muscle contractility, the processes responsible for decreased force output with altered metabolism are also likely to be many, acting in concert, rather than the actions of one altered parameter. Nevertheless the aim of this study is to elucidate the hierarchical series of events that contribute to reduced smooth muscle force production during altered metabolism. We conclude that in many phasic smooth muscles the decrease in force can be attributed to impaired electro-mechanical coupling whereby the Ca2+ transient is reduced. A direct effect of hypoxia on the Ca2+ channel may be of key importance. In tonic vascular smooth muscles KATP channels may also play a role in the integrated functional responses to hypoxia. There are also many examples of force being reduced, in tonically activated preparations, without a fall in steady-state Ca2+; indeed it usually increases. We examine the roles of altered [ATP], pH, myosin phosphorylation, inorganic phosphate and proteolytic activity on the [Ca2+]-force relationship during hypoxia. We find no defining force-inhibitory role for any one factor acting alone, and suggest that force most probably falls as a result of the combination of myriad factors.
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71
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Smith GL, Austin C, Crichton C, Wray S. A review of the actions and control of intracellular pH in vascular smooth muscle. Cardiovasc Res 1998; 38:316-31. [PMID: 9709392 DOI: 10.1016/s0008-6363(98)00020-0] [Citation(s) in RCA: 66] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/08/2023] Open
Abstract
OBJECTIVE This review is an account of the physiological issues involved in the effects of pH on vascular smooth muscle tone. The following criteria were considered when reviewing the literature: (i) the type of smooth muscle, i.e. either tonic or phasic, (ii) the source of the smooth muscle i.e. pulmonary, systemic, large artery, resistance artery, vein or cell line, (iii) the effects of changing intracellular or extracellular pH alone, (iv) the acute or chronic effects of altered pH (v) the influence of extracellular pH on intracellular pH and (vi) the influence of altered intracellular pH on basal or agonist induced tone. Studies of the effects of pH on the individual intracellular components of vascular tone, specifically sarcoplasmic reticulum and contractile proteins function are considered. Finally, the pH sensitivity of molecular components that contribute to smooth muscle cell tone are reviewed. CONCLUSIONS There appear to be distinct differences in the response of large arteries and resistance arteries to altered intracellular pH which may be based on the different properties of the smooth muscle within the wall of each blood vessel. Similarly, systemic and pulmonary vessels may respond differently, but no systematic study exists to allow a more definitive conclusion. Factors controlling intracellular pH such as intracellular buffering power and sarcolemmal pH regulating mechanisms may differ across the vascular bed and may contribute to some of the differences observed in response to altered extracellular pH. Finally, few studies have examined the pH sensitivity the intracellular processes involved in basal tone and pharmaco-mechanical coupling in vascular smooth muscle. More information concerning these latter aspects of smooth muscle function is required to progress the understanding of the modulator action on pH on vascular tone.
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Larcombe-McDouall JB, Harrison N, Wray S. The in vivo relationship between blood flow, contractions, pH and metabolites in the rat uterus. Pflugers Arch 1998; 435:810-7. [PMID: 9518510 DOI: 10.1007/s004240050588] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Little is known about the relationship between smooth muscle contractile activity and its blood supply. We have therefore investigated this in the rat uterus, using laser-Doppler flow measurement and intra-uterine pressure recordings. We found an inverse linear relationship between flow and contractile activity. There was no evidence for a critical level of flow, above which function is maintained and below which it declines; even small reductions in blood flow decreased uterine force. Force was rapidly restored upon reperfusion. Reactive hyperaemia was absent from all but 6 of the 41 preparations studied. We used 31P nuclear magnetic resonance (NMR) spectroscopy to measure concentrations of adenosine triphosphate (ATP), phosphocreatine (PCr), inorganic phosphate (Pi) and intracellular pH (pHi) simultaneously with force and flow. Reductions in flow were associated with significant reductions in [ATP], [PCr] and pHi, and an increase in [Pi]. These changes were related to flow significantly and linearly and their effects on force may be additive. These data show that uterine smooth muscle is closely dependent upon its blood supply for maintaining both normal force production and metabolite levels. Consequently, even small decrements in flow may have deleterious functional effects.
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Fueshko SM, Key S, Wray S. GABA inhibits migration of luteinizing hormone-releasing hormone neurons in embryonic olfactory explants. J Neurosci 1998; 18:2560-9. [PMID: 9502815 PMCID: PMC6793115] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
During development, a subpopulation of olfactory neurons transiently expresses GABA. The spatiotemporal pattern of GABAergic expression coincides with migration of luteinizing hormone-releasing hormone (LHRH) neurons from the olfactory pit to the CNS. In this investigation, we evaluated the role of GABAergic input on LHRH neuronal migration using olfactory explants, previously shown to exhibit outgrowth of olfactory axons, migration of LHRH neurons in association with a subset of these axons, and the presence of the olfactory-derived GABAergic neuronal population. GABAA receptor antagonists bicuculline (10(-5) M) or picrotoxin (10(-4) M) had no effect on the length of peripherin-immunoreactive olfactory fibers or LHRH cell number. However, LHRH cell migration, as determined by the distance immunopositive cells migrated from olfactory pits, was significantly increased by these perturbations. Addition of tetrodotoxin (10(-6) M), to inhibit Na+-transduced electrical activity, also significantly enhanced LHRH migration. The most robust effect observed was dramatic inhibition of LHRH cell migration in explants cultured in the presence of the GABAA receptor agonist muscimol (10(-4) M). This study demonstrates that GABAergic activity in nasal regions can have profound effects on migration of LHRH neurons and suggests that GABA participates in appropriate timing of LHRH neuronal migration into the developing brain.
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Burdyga TV, Taggart MJ, Crichton C, Smith GL, Wray S. The mechanism of Ca2+ release from the SR of permeabilised guinea-pig and rat ureteric smooth muscle. BIOCHIMICA ET BIOPHYSICA ACTA 1998; 1402:109-14. [PMID: 9551092 DOI: 10.1016/s0167-4889(97)00149-3] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Recent work has indicated that there is a major difference in the Ca2+ store of smooth muscle from rat and guinea-pig ureter; with the rat store being agonist-sensitive but ryanodine insensitive and the guinea-pig store being ryanodine sensitive but agonist insensitive [Th. V. Burdyga, M.J. Taggart, S. Wray, J. Physiol. 489 (1995) 327-335]. We have therefore examined directly the mechanism of Ca2+ release from the internal Ca2+ store (SR). Following permeabilisation with alpha-toxin or beta-escin the SR was Ca(2+)-loaded before application of carbachol or caffeine. Only carbachol evoked a transient contraction in rat ureter. The carbachol-induced contraction was blocked by heparin and cyclopiazonic acid (CPA) but not ryanodine. Only caffeine produced contraction in guinea-pig ureter, and this was blocked by ryanodine. Direct application of IP3 caused a small transient contraction in rat but not guinea-pig ureter. We conclude that rat ureter possesses only an IP3 sensitive store while guinea-pig ureter only has a ryanodine sensitive store.
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Bullock AJ, Duquette RA, Buttell N, Wray S. Developmental changes in intracellular pH buffering power in smooth muscle. Pflugers Arch 1998; 435:575-7. [PMID: 9446707 DOI: 10.1007/s004240050555] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Intracellular pH (pHi) is known to modulate contraction. Neonatal tissues can differ from adult tissue in contractile response to stimuli known to alter pHi e.g. hypoxia. Changes of pH are attenuated by buffering, thus any difference in buffering power (beta) between tissues could affect their functional response to pHi perturbation. Similarly the extent to which any extracellular pH (pHo) alteration is transmitted into a pHi change will also influence function. We have therefore determined the intrinsic beta and effect of pHo change on pHi in neonatal and adult ureteric, uterine and gastric smooth muscles using the pH-sensitive fluorophore carboxy-SNARF. beta was found to be similar in the three adult tissues, but there were significant differences between neonatal tissues. In contrast, we found little difference in the amount of pHi change produced by pHo change between neonatal and adult tissues from the same smooth muscle, but a difference between smooth muscles. These data highlight significant differences between smooth muscles and their developmental state, which may contribute to different degrees of protection when pH is perturbed.
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