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  • 1
    Electronic Resource
    Electronic Resource
    Basic properties of an inositol 1,4,5-trisphosphate-gated channel in carp olfactory cilia (2000)
    Oxford, UK : Blackwell Science Ltd
    European journal of neuroscience 12 (2000), S. 0 
    Details
    ISSN: 1460-9568
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: In addition to the activation of cAMP-dependent pathways, odorant binding to its receptor can lead to inositol 1,4,5-trisphosphate (InsP3) production that may induce the opening of plasma membrane channels. We therefore investigated the presence and nature of such channels in carp olfactory cilia. Functional analysis was performed by reconstitution of the olfactory cilia in planar lipid bilayers (tip-dip method). In the presence of InsP3 (10 μm) and Ca2+ (100 n m), a current of 1.6 ± 0.1 pA (mean ± SEM, n = 4) was measured, using Ba2+ as charge carrier. The I/V curve displayed a slope conductance of 45 ± 5 pS and a reversal potential of −29 mV indicating a higher selectivity for divalent cations. This current was characterized by two mean open times (3.0 ± 0.4 ms and 42.0 ± 2.6 ms, n = 4) and was strongly inhibited by ruthenium red (30 μm) or heparin (10 μg/mL). Importantly, the channel activity was closely dependent on the Ca2+ concentration, with the highest open probability (Po) at 100 n m Ca2+ (Po = 0.50 ± 0.02, n = 4). Po is lower at both higher and lower Ca2+ concentrations. A structural identification of the channel was attempted by using a large panel of antibodies, raised against several InsP3 receptor (InsP3R)/Ca2+ release channel isoforms. The type 1 InsP3R was detected in carp cerebellum and whole brain, while a lower molecular mass InsP3R, which may correspond to type 2 or 3, was detected in heart, whole brain and the soma of the olfactory neurons. None of the antibodies, however, cross-reacted with olfactory cilia. Taken together, these results indicate that in carp olfactory cilia an InsP3-dependent channel is present, distinct from the classical InsP3Rs localized on intracellular membranes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1460-9568.2000.00166.x
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  • 2
    Electronic Resource
    Electronic Resource
    Vasopressin responses in electrically coupled A7r5 cells (1994)
    Springer
    Pflügers Archiv 428 (1994), S. 283-287 
    Details
    ISSN: 1432-2013
    Keywords: Ca2+ oscillations ; Ca2+ wave ; Smooth muscle ; Spontaneous electrical activity ; Ca2+ imaging
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Changes in cytosolic Ca2+ concentration ([Ca2+]i) and in membrane potential were monitored in single A7r5 smooth-muscle cells during spontaneous spiking and after arginine vasopressin stimulation. Spontaneous Ca2+ oscillations, which were associated with the occurrence of action potentials, occurred in about 90% of the confluent monolayers investigated. This spontaneous activity was synchronized amongst all the cells of the monolayer, indicating that the cells were electrically coupled. Arginine vasopressin stimulation produced a [Ca2+]i rise that was about 5 times higher than the amplitude of the spontaneous Ca2+ oscillations and resulted in a subsequent cessation of spontaneous electrical activity and associated Ca2+ spiking, which persisted after [Ca2+]i returned to baseline. Individual cells in the monolayer responded to arginine vasopressin with a different latency. Agonist-induced Ca2+ waves within one cell propagated much more slowly than spontaneous [Ca2+]i rises. We conclude that agonist-induced [Ca2+]i increases in an electrically coupled cell monolayer can be asynchronous.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00724508
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  • 3
    Electronic Resource
    Electronic Resource
    Bell-shaped activation of inositol-1,4,5-trisphosphate-induced Ca2+ release by thimerosal in permeabilized A7r5 smooth-muscle cells (1993)
    Springer
    Pflügers Archiv 424 (1993), S. 516-522 
    Details
    ISSN: 1432-2013
    Keywords: Thimerosal ; Ins(1,4,5)P 3 receptor ; Ca2+ signalling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract There is no consensus about the different types of Ca2+ transport processes in the endoplasmic reticulum that are targeted by the sulphydryl reagent thimerosal. We have therefore investigated how thimerosal affects the various Ca2+ transport processes in permeabilized A7r5 smooth-muscle cells, using an unidirectional 45Ca2+ flux technique. Thimerosal up to a concentration of 32 μM did not have an effect on the passive 45Ca2+ leak from the stores, while higher concentrations increased this aspecific leak. Thimerosal inhibited the endoplasmic reticulum Ca2+ pump with an EC50 of 9 μM. Thimerosal exerted a biphasic effect on the Ca2+ release induced by inositol 1,4,5-trisphosphate [Ins(1,4,5)P 3] with a stimulation of the release at thimerosal concentrations below 10 μM, and an inhibitory effect at higher concentrations. Thimerosal (2.5–250 μM) did not exert an effect on the specific binding of [3H]Ins(1,4,5)P 3 to its receptor, indicating that it probably did not act at the level of the binding site. This finding contrasts with the effect of the closely related sulphydryl reagent parachloromercuriphenylsulphonate, which, at high concentrations, inhibited [3H]Ins(1,4,5)P 3 binding. The effects of thimerosal were largely prevented by the sulphydryl reducing agent dithiothreitol (3 mM). We conclude that thimerosal concentrations ranging from 0.32 to 1 μM can stimulate the Ins(1,4,5)P 3-induced Ca2+ release without inhibiting the Ca2+ pumps or without increasing the passive Ca2+ permeability of the endoplasmic reticulum.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00374916
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  • 4
    Electronic Resource
    Electronic Resource
    Normal Ca2+ signalling in glutathione-depleted and dithiothreitol-treated HeLa cells (1993)
    Springer
    Pflügers Archiv 423 (1993), S. 480-484 
    Details
    ISSN: 1432-2013
    Keywords: Cytosolic Ca2+ signal ; Thiol reagent ; HeLa cells
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract We have investigated whether reducing agents and substances that interfere with glutathione metabolism would affect the histamine-induced rises in internal Ca2+ concentration ([Ca2+]i) in indo-1-loaded HeLa cells. Individual cells responded to 1 μM histamine with either baseline or sinusoidal Ca2+ oscillations, a single Ca2+ peak or a maintained elevation of the [Ca2+]i. Only a few cells did not respond. The sulphydryl reducing agent dithiothreitol (5 mM) did not affect these responses to histamine. A 24-h preincubation with 1 mM dl-buthionine (SR)-sulphoximine, which reduces the cellular glutathione content to less than 20% of its control value, affected neither these histamine responses, nor the [Ca2+]i rises after application of 2 μM thapsigargin. We conclude that oxidation of critical sulphydryl groups is not required for the normal response to histamine and also that glutathione plays no role in agonistinduced Ca2+ signalling in HeLa cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00374944
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  • 5
    Electronic Resource
    Electronic Resource
    Regulation of the Na+-dependent and the Na+-independent polyamine transporters in renal epithelial cells (LLC-PK1) (1990)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 144 (1990), S. 365-375 
    Details
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: We have studied the regulation of the Na+-dependent and Na+-independent polyamine transport pathways in the renal LLC-PK1 cell line. Most of the experiments were performed in the presence of 5 mM DL-2-difluoromethylornithine (DFMO) in order to inhibit the cellular synthesis of polyamines. The activity of both transporters as measured by putrescine uptake was increased by growth-promoting stimuli and decreased by exogenous polyamines. The time course of the increase in uptake activity induced by fetal calf serum could be fitted by a single exponential, and the process was three times faster for the Na+-dependent than for the Na+-independent transporter. Maximum activity was reached after more than 24 h. This increase could be inhibited by actinomycin D and by cycloheximide. Other growth-promoting stimuli, such as subconfluent cell density, as well as growth factors also induced an increase in the transport activity. Particularly, there was a marked stimulation of the Na+-dependent pathway by epidermal growth factor in combination with insulin. On the other hand, the transport activity decayed very rapidly upon addition of exogenous polyamines (t1/2 〈 60 min). The diamine putrescine was much less effective in this respect than the polyamines spermidine and spermine. The non-metabolizable substrate methylglyoxal bis(guanylhydrazone) did not induce a decay of the transport activity, but it protected the Na+-dependent pathway against the polyamine-in-duced decay. Inhibition of the protein synthesis by cycloheximide did not induce a rapid decrease of the transport activity; neither did it affect the polyamine-induced decay. These observations suggest that this polyamine-induced decay is not owing to an inhibitory effect on the rate of synthesis of the transporters, but rather to a degradation or an inactivation of the transporters. The polyamine-induced decay slowed down at lower cell density. This effect was particularly pronounced for the Na+-dependent transporter. Since the uptake of polyamines was increased at low cell density, the decreased rate of decay in this condition pleads against a simple mechanism of transinhibition by the substrate. In conclusion, both transport pathways were similarly affected by the regulatory parameters, but the Na+-deperdent transporter was more rapidly and more effectively regulated. The numerous interacting regulatory steps furthermore suggest a Physiological role for these transporters, such as an involvement in urinary polyamine disposal.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcp.1041440302
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