scholarly journals Connections Between Connexins, Calcium, and Cataracts in the Lens

2004 ◽  
Vol 124 (4) ◽  
pp. 289-300 ◽  
Author(s):  
Junyuan Gao ◽  
Xiurong Sun ◽  
Francisco J. Martinez-Wittinghan ◽  
Xiaohua Gong ◽  
Thomas W. White ◽  
...  
Keyword(s):  
Calcium Concentration ◽  
Circulatory System ◽  
Good Deal ◽  
Cell Contact ◽  
Concentration Data ◽  
Fiber Cells ◽  
Calcium Dependent ◽  
Cytoplasmic Proteins ◽  
Junction Coupling ◽  
Coupling Conductance

There is a good deal of evidence that the lens generates an internal micro circulatory system, which brings metabolites, like glucose, and antioxidants, like ascorbate, into the lens along the extracellular spaces between cells. Calcium also ought to be carried into the lens by this system. If so, the only path for Ca2+ to get out of the lens is to move down its electrochemical gradient into fiber cells, and then move by electrodiffusion from cell to cell through gap junctions to surface cells, where Ca-ATPase activity and Na/Ca exchange can transport it back into the aqueous or vitreous humors. The purpose of the present study was to test this calcium circulation hypothesis by studying calcium homeostasis in connexin (Cx46) knockout and (Cx46 for Cx50) knockin mouse lenses, which have different degrees of gap junction coupling. To measure intracellular calcium, FURA2 was injected into fiber cells, and the gradient in calcium concentration from center to surface was mapped in each type of lens. In wild-type lenses the coupling conductance of the mature fibers was ∼0.5 S/cm2 of cell to cell contact, and the best fit to the calcium concentration data varied from 700 nM in the center to 300 nM at the surface. In the knockin lenses, the coupling conductance was ∼1.0 S/cm2 and calcium varied from ∼500 nM at the center to 300 nM at the surface. Thus, when the coupling conductance doubled, the concentration gradient halved, as predicted by the model. In knockout lenses, the coupling conductance was zero, hence the efflux path was knocked out and calcium accumulated to ∼2 μM in central fibers. Knockout lenses also had a dense central cataract that extended from the center to about half the radius. Others have previously shown that this cataract involves activation of a calcium-dependent protease, Lp82. We can now expand on this finding to provide a hypothesis on each step that leads to cataract formation: knockout of Cx46 causes loss of coupling of mature fiber cells; the efflux path for calcium is therefore blocked; calcium accumulates in the central cells; at concentrations above ∼1 μM (from the center to about half way out of a 3-wk-old lens) Lp82 is activated; Lp82 cleaves cytoplasmic proteins (crystallins) in central cells; and the cleaved proteins aggregate and scatter light.

The origin of passive force enhancement in skeletal muscle

2008 ◽  
Vol 294 (1) ◽  
pp. C74-C78 ◽  
Author(s):  
V. Joumaa ◽  
D. E. Rassier ◽  
T. R. Leonard ◽  
W. Herzog
Keyword(s):  
Calcium Concentration ◽  
Force Production ◽  
Primary Source ◽  
Passive Force ◽  
Active Force ◽  
Force Enhancement ◽  
Bridge Formation ◽  
Calcium Dependent ◽  
Cross Bridge ◽  
High Calcium

The aim of the present study was to test whether titin is a calcium-dependent spring and whether it is the source of the passive force enhancement observed in muscle and single fiber preparations. We measured passive force enhancement in troponin C (TnC)-depleted myofibrils in which active force production was completely eliminated. The TnC-depleted construct allowed for the investigation of the effect of calcium concentration on passive force, without the confounding effects of actin-myosin cross-bridge formation and active force production. Passive forces in TnC-depleted myofibrils ( n = 6) were 35.0 ± 2.9 nN/ μm2 when stretched to an average sarcomere length of 3.4 μm in a solution with low calcium concentration (pCa 8.0). Passive forces in the same myofibrils increased by 25% to 30% when stretches were performed in a solution with high calcium concentration (pCa 3.5). Since it is well accepted that titin is the primary source for passive force in rabbit psoas myofibrils and since the increase in passive force in TnC-depleted myofibrils was abolished after trypsin treatment, our results suggest that increasing calcium concentration is associated with increased titin stiffness. However, this calcium-induced titin stiffness accounted for only ∼25% of the passive force enhancement observed in intact myofibrils. Therefore, ∼75% of the normally occurring passive force enhancement remains unexplained. The findings of the present study suggest that passive force enhancement is partly caused by a calcium-induced increase in titin stiffness but also requires cross-bridge formation and/or active force production for full manifestation.

scholarly journals Calcium influx into neurons can solely account for cell contact-dependent neurite outgrowth stimulated by transfected L1.

1992 ◽  
Vol 119 (4) ◽  
pp. 883-892 ◽  
Author(s):  
E J Williams ◽  
P Doherty ◽  
G Turner ◽  
R A Reid ◽  
J J Hemperly ◽  
...  
Keyword(s):  
Neurite Outgrowth ◽  
Pc12 Cells ◽  
Calcium Influx ◽  
Polysialic Acid ◽  
Cell Contact ◽  
3T3 Cells ◽  
Cerebellar Neurons ◽  
Calcium Dependent ◽  
Promote Neurite Outgrowth ◽  
Neural Cell Adhesion

We have used monolayers of control 3T3 cells and 3T3 cells expressing transfected human L1 as a culture substrate for rat PC12 cells and rat cerebellar neurons. PC12 cells and cerebellar neurons extended longer neurites on human L1 expressing cells. Neurons isolated from the cerebellum at postnatal day 9 responded equally as well as those isolated at postnatal day 1-4, and this contrasts with the failure of these older neurons to respond to the transfected human neural cell adhesion molecule (NCAM). Human L1-dependent neurite outgrowth could be blocked by antibodies that bound to rat L1 and, additionally, the response could be fully inhibited by pertussis toxin and substantially inhibited by antagonists of L- and N-type calcium channels. Calcium influx into neurons induced by K+ depolarization fully mimics the L1 response. Furthermore, we show that L1- and K+(-)dependent neurite outgrowth can be specifically inhibited by a reduction in extracellular calcium to 0.25 microM, and by pretreatment of cerebellar neurons with the intracellular calcium chelator BAPTA/AM. In contrast, the response was not inhibited by heparin or by removal of polysialic acid from neuronal NCAM both of which substantially inhibit NCAM-dependent neurite outgrowth. These data demonstrate that whereas NCAM and L1 promote neurite outgrowth via activation of a common CAM-specific second messenger pathway in neurons, neuronal responsiveness to NCAM and L1 is not coordinately regulated via posttranslational processing of NCAM. The fact that NCAM- and L1-dependent neurite outgrowth, but not adhesion, are calcium dependent provides further evidence that adhesion per se does not directly contribute to neurite outgrowth.

scholarly journals Resting Tension Affects eNOS Activity in a Calcium-Dependent Way in Airways

2007 ◽  
Vol 2007 ◽  
pp. 1-6 ◽  
Author(s):  
Eudoxia Kitsiopoulou ◽  
Apostolia A. Hatziefthimiou ◽  
Konstantinos I. Gourgoulianis ◽  
Paschalis-Adam Molyvdas
Keyword(s):  
Nitric Oxide ◽  
Smooth Muscle ◽  
Calcium Concentration ◽  
Kinase Inhibitors ◽  
Calcium Dependent ◽  
Enos Activity ◽  
Resting Tension ◽  
Smooth Muscle Contractions ◽  
Oxide Synthase ◽  
Inducible Nos

The alteration of resting tension (RT) from 0.5 g to 2.5 g increased significantly airway smooth muscle contractions induced by acetylcholine (ACh) in rabbit trachea. The decrease in extracellular calcium concentration[Ca2+]ofrom 2 mM to 0.2 mM reduced ACh-induced contractions only at 2.5 g RT with no effect at 0.5 g RT. The nonselective inhibitor of nitric oxide synthase (NOS),NG-nitro-L-arginine methyl ester (L-NAME) increased ACh-induced contractions at 2.5 g RT. The inhibitor of inducible NOS, S-methylsothiourea or neuronal NOS, 7-nitroindazole had no effect. At 2.5 g RT, the reduction of[Ca2+]ofrom 2 mM to 0.2 mM abolished the effect of L-NAME on ACh-induced contractions. The NO precursor L-arginine or the tyrosine kinase inhibitors erbstatin A and genistein had no effect on ACh-induced contractions obtained at 2.5 g RT. Our results suggest that in airways, RT affects ACh-induced contractions by modulating the activity of epithelial NOS in a calcium-dependent, tyrosine-phosphorylation-independent way.

scholarly journals Gap Junctional Coupling in Lenses from α8 Connexin Knockout Mice

2001 ◽  
Vol 118 (5) ◽  
pp. 447-456 ◽  
Author(s):  
George J. Baldo ◽  
Xiaohua Gong ◽  
Francisco J. Martinez-Wittinghan ◽  
Nalin M. Kumar ◽  
Norton B. Gilula ◽  
...  
Keyword(s):  
Gap Junctions ◽  
Inner Core ◽  
Wild Type Mouse ◽  
Fiber Cell ◽  
Cell Contact ◽  
Wild Type ◽  
Cell Coupling ◽  
Genetically Engineered Mice ◽  
Lens Physiology ◽  
Coupling Conductance

Lens fiber cell gap junctions contain α3 (Cx46) and α8 (Cx50) connexins. To examine the roles of the two different connexins in lens physiology, we have genetically engineered mice lacking either α3 or α8 connexin. Intracellular impedance studies of these lenses were used to measure junctional conductance and its sensitivity to intracellular pH. In Gong et al. 1998, we described results from α3 connexin knockout lenses. Here, we present original data from α8 connexin knockout lenses and a comparison with the previous results. The lens has two functionally distinct domains of fiber cell coupling. In wild-type mouse lenses, the outer shell of differentiating fibers (see 1, DF) has an average coupling conductance per area of cell–cell contact of ∼1 S/cm2, which falls to near zero when the cytoplasm is acidified. In the inner core of mature fibers (see 1, MF), the average coupling conductance is ∼0.4 S/cm2, and is insensitive to acidification of the cytoplasm. Both connexin isoforms appear to contribute about equally in the DF since the coupling conductance for either heterozygous knockout (+/−) was ∼70% of normal and 30–40% of the normal for both −/− lenses. However, their contribution to the MF was different. About 50% of the normal coupling conductance was found in the MF of α3 +/− lenses. In contrast, the coupling of MF in the α8 +/− lenses was the same as normal. Moreover, no coupling was detected in the MF of α3 −/− lenses. Together, these results suggest that α3 connexin alone is responsible for coupling MF. The pH- sensitive gating of DF junctions was about the same in wild-type and α3 connexin −/− lenses. However, in α8 −/− lenses, the pure α3 connexin junctions did not gate closed in the response to acidification. Since α3 connexin contributes about half the coupling conductance in DF of wild-type lenses, and that conductance goes to zero when the cytoplasmic pH drops, it appears α8 connexin regulates the gating of α3 connexin. Both connexins are clearly important to lens physiology as lenses null for either connexin lose transparency. Gap junctions in the MF survive for the lifetime of the organism without protein turnover. It appears that α3 connexin provides the long-term communication in MF. Gap junctions in DF may be physiologically regulated since they are capable of gating when the cytoplasm is acidified. It appears α8 connexin is required for gating in DF.

scholarly journals Anti-Allergy Potential of Averrhoa bilimbi Linn. Fruit Water Extract Shown by Its Suppressive Effect on the Degranulation of RBL-2H3 Cells

2021 ◽  
pp. 81-88
Author(s):  
William Halim Santoso ◽  
Momoko Ishida ◽  
Kosuke Nishi ◽  
Takuya Sugahara ◽  
Agus Budiawan Naro Putra
Keyword(s):  
Calcium Concentration ◽  
Water Extract ◽  
Allergic Diseases ◽  
Suppressive Effect ◽  
Inhibitory Effect ◽  
Current Evidence ◽  
Polyphenol Content ◽  
Calcium Dependent ◽  
Active Substances

Allergy rhinitis (AR), as reported by the World Allergy Organization (WAO), is one of the highest prevalence allergies affecting 10-30% of all adults and up to 40% of children. In Indonesia, current evidence showed that the prevalence of AR is increasing. Averrhoa bilimbi Linn. fruit (AF), or locally known as belimbing wuluh, has been scientifically proven to treat many diseases due to the abundant of polyphenol content which was shown to have the potential to treat allergies. Therefore, this study was aimed to investigate the anti-allergy potential of AF in vitro. The anti-allergy effect of Averrhoa bilimbi Linn. fruit water extract (AFWE) was examined using RBL-2H3 cells. At first, the cytotoxicity effect of AFWE was determined by WST-8 assay. The release of β-hexosaminidase by RBL-2H3 cells was also measured to evaluate degranulation suppression activity of AFWE. Lastly, calcium assay was employed to investigate the intracellular calcium concentration ([Ca­2+]i). Results demonstrated that AFWE does not show any cytotoxicity at any given concentration. In addition, AFWE at 1.25 mg/mL showed sufficient inhibitory effect towards degranulation by RBL-2H3 cells. Moreover, the degranulation-suppressing activity of AFWE was resulted from the inhibition of calcium-dependent signaling pathways. Unfortunately, the properties of active substances from AFWE have not been investigated. To conclude, this study indicated that AFWE has potential as an alternative treatment for allergic diseases.

scholarly journals Effects of caffeine, tetracaine, and ryanodine on calcium-dependent oscillations in sheep cardiac Purkinje fibers.

1985 ◽  
Vol 86 (6) ◽  
pp. 877-889 ◽  
Author(s):  
C J Nieman ◽  
D A Eisner
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Intracellular Calcium ◽  
Calcium Concentration ◽  
Oscillation Amplitude ◽  
Membrane Current ◽  
Inward Current ◽  
Purkinje Fibers ◽  
Calcium Dependent ◽  
Cardiac Purkinje Fibers ◽  
High Concentrations

Membrane current and tension were measured in voltage-clamped sheep cardiac Purkinje fibers. Elevating the intracellular calcium concentration ([Ca2+]i) results in oscillations of membrane current and tension both at rest and during stimulation. During stimulation, an oscillatory transient inward current and an after contraction follow repolarization. We have examined the effects on the oscillations of changing the extracellular calcium concentration ([Ca2+]o) and of adding various drugs. In agreement with previous work, high concentrations of drugs that affect the sarcoplasmic reticulum, namely caffeine (10-20 mM), tetracaine (1 mM), and ryanodine (10 microM), abolish the oscillations. However, at lower concentrations, these three drugs have different effects on the oscillations. Caffeine (1-2 mM) decreases the oscillation amplitude but increases the frequency. Tetracaine (100-500 microM) has little effect on the magnitude of the oscillations but decreases their frequency. Ryanodine, at all concentrations used (0.1-10 microM), eventually abolishes the oscillations but, in doing so, decreases the magnitude, leaving the frequency unaffected. When [Ca2+]o was changed in order to vary [Ca2+]i, both the frequency and the magnitude of the oscillations always changed in the same direction. This suggests that these three drugs have effects in addition to just changing [Ca2+]i.

Characterization of the interactions of alpha-catenin with alpha-actinin and beta-catenin/plakoglobin

1997 ◽  
Vol 110 (8) ◽  
pp. 1013-1022 ◽  
Author(s):  
J.E. Nieset ◽  
A.R. Redfield ◽  
F. Jin ◽  
K.A. Knudsen ◽  
K.R. Johnson ◽  
...  
Keyword(s):  
Cell Adhesion ◽  
Protein Interactions ◽  
Beta Catenin ◽  
Protein Protein Interactions ◽  
Yeast Two Hybrid ◽  
Calcium Dependent ◽  
Cytoplasmic Proteins ◽  
Dependent Cell ◽  
Two Hybrid ◽  
Cell Cell

Cadherins are calcium-dependent, cell surface glycoproteins involved in cell-cell adhesion. To function in cell-cell adhesion, the transmembrane cadherin molecule must be associated with the cytoskeleton via cytoplasmic proteins known as catenins. Three catenins, alpha-catenin, beta-catenin and gamma-catenin (also known as plakoglobin), have been identified. beta-catenin or plakoglobin is associated directly with the cadherin; alpha-catenin binds to beta-catenin/plakoglobin and serves to link the cadherin/catenin complex to the actin cytoskeleton. The domains on the cadherin and betacatenin/plakoglobin that are responsible for protein-protein interactions have been mapped. However, little is known about the molecular interactions between alpha-catenin and beta-catenin/plakoglobin or about the interactions between alpha-catenin and the cytoskeleton. In this study we have used the yeast two-hybrid system to map the domains on alpha-catenin that allow it to associate with beta-catenin/plakoglobin and with alpha-actinin. We also identify a region on alpha-actinin that is responsible for its interaction with alpha-catenin. The yeast two-hybrid data were confirmed with biochemical studies.

scholarly journals Activity-dependent increases in [Ca2+]i contribute to digital-analog plasticity at a molluscan synapse

2017 ◽  
Vol 117 (6) ◽  
pp. 2104-2112 ◽  
Author(s):  
Bjoern Ch. Ludwar ◽  
Colin G. Evans ◽  
Monica Cambi ◽  
Elizabeth C. Cropper
Keyword(s):  
Synaptic Transmission ◽  
Intracellular Calcium ◽  
Time Constant ◽  
Calcium Concentration ◽  
Low Frequency ◽  
Intracellular Calcium Concentration ◽  
Calcium Signal ◽  
Presynaptic Neuron ◽  
Calcium Dependent ◽  
Long Time

In a type of short-term plasticity that is observed in a number of systems, synaptic transmission is potentiated by depolarizing changes in the membrane potential of the presynaptic neuron before spike initiation. This digital-analog form of plasticity is graded. The more depolarized the neuron, the greater the increase in the efficacy of synaptic transmission. In a number of systems, including the system presently under investigation, this type of modulation is calcium dependent, and its graded nature is presumably a consequence of a direct relationship between the intracellular calcium concentration ([Ca2+]i) and the effect on synaptic transmission. It is therefore of interest to identify factors that determine the magnitude of this type of calcium signal. We studied a synapse in Aplysia and demonstrate that there can be a contribution from currents activated during spiking. When neurons spike, there are localized increases in [Ca2+]i that directly trigger neurotransmitter release. Additionally, spiking can lead to global increases in [Ca2+]i that are reminiscent of those induced by subthreshold depolarization. We demonstrate that these spike-induced increases in [Ca2+]i result from the activation of a current not activated by subthreshold depolarization. Importantly, they decay with a relatively slow time constant. Consequently, with repeated spiking, even at a low frequency, they readily summate to become larger than increases in [Ca2+]i induced by subthreshold depolarization alone. When this occurs, global increases in [Ca2+]i induced by spiking play the predominant role in determining the efficacy of synaptic transmission. NEW & NOTEWORTHY We demonstrate that spiking can induce global increases in the intracellular calcium concentration ([Ca2+]i) that decay with a relatively long time constant. Consequently, summation of the calcium signal occurs even at low firing frequencies. As a result there is significant, persistent potentiation of synaptic transmission.

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