Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 2
    ISSN: 1460-9568
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Down-regulation of T-type Ca channel current and mRNA occurs following differentiation of Y79 retinoblastoma cells. To understand how the decrease in expression is linked to cell differentiation, we examined transcriptional regulation of the Cav3.1 Ca channel gene, CACNA1G. We identified two putative promoters (A and B) in 1.3 kb of cloned genomic DNA. Reverse transcriptase-polymerase chain reaction and 5′ rapid amplification of cDNA ends-polymerase chain reaction analyses demonstrated that two transcripts with different 5′ untranslated regions are generated by different transcription start sites, with promoter A favoured in undifferentiated cells and promoter B favoured in differentiated cells. Functional analyses of the promoter sequence revealed that both promoters are active. Enhancer and repressor sequences were identified upstream of promoter A and B, respectively. These results suggest that the down-regulation of α1G mRNA in differentiated Y79 cells is mediated primarily by decreased activity of promoter A, which could occur in conjunction with repression of the activity of promoter B. The decrease in T-type Ca channel expression in Y79 cells may be an essential signal affecting phenotypic maturation and expression of other ion channel subtypes in the differentiated cells.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 3
    ISSN: 1432-1424
    Keywords: K+ channel ; inward rectification ; patch clamp
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Ionic conductances of rabbit osteoclasts were investigated using both whole-cell and cell-attached configurations of the patch-clamp recording technique. The predominant conductance found in these cells was an inwardly rectifying K+ conductance. Whole-cell currents showed an N-shaped current-voltage (I−13;V) relation with inward current activated at potentials negative to EK. When external K+ was varied, I-V curves shifted 53 mV/10-fold change in [K+]out, as predicted for a K+-selective channel. Inward current was blocked by Ba2+ and showed a time-dependent decline at negative potentials, which was reduced in Na+-free external solution. Inward single-channel currents were recorded in the cell-attached configuration. Single-channel currents were identified as inward-rectifier K+ channels based on the following observations: (i) Unitary I-V relations rectified, with only inward current resolved. (ii) Unitary conductance (γ) was 31 pS when recorded in the cell-attached configuration with 140 mm K+ in the pipette and was found to be dependent on [K+]. (iii) Addition of Ba2+ to the pipette solution abolished single-channel events. We conclude that rabbit osteoclasts possess inwardly rectifying K+ channels which give rise to the inward current recorded at negative potentials in the whole-cell configuration. This inwardly rectifying K+ current may be responsible for setting the resting membrane potential and for dissipating electrical potential differences which arise from electrogenic transport of protons across the osteoclast ruffled border.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 4
    ISSN: 1432-2013
    Keywords: 3,4-Diaminopyridine ; Delayed rectifier ; Spike frequency adaptation ; Potassium channels ; Action potential ; Bullfrog sympathetic ganglion neurones
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Neurones of the bullfrog sympathetic ganglion exhibit at least 5 distinct K+ currents. Two calcium-dependent K+ currentsI C andI AHP, the delayed rectifierI K, the muscarinic-sensitiveI M and the transient outward currentI A. Each current plays a unique role in controlling the shapes and firing patterns of action potentials observed in these neurones. We have found that 3,4-diaminopyridine (DAP) (〉0.1 mM) will selectively blockI K andI A. Concentrations as high as 2 mM have no effect onI C,I AHP orI M. SinceI A is mostly inactivated at resting potentials in these cells, DAP can be used to explore the electrophysiological function ofI K. Under normal conditions DAP has no effect on action potential duration or on patterns of repetitive activity. This indicates thatI K is normally not involved in modulating these parameters. WhenI C andI AHP are blocked by removing extracellular calcium, however, inhibition ofI K prolongs action potential duration, reduces a fast afterhypolarization and enhances spike frequency adaptation. WhenI M andI AHP are reduced by barium (1 mM), inhibition ofI K by DAP has smaller effects on action potential duration and atterhyperpolarization amplitude, but still enhances spike frequency adaptation. We conclude that electrophysiological effects of blockingI K are critically dependent on the levels of other K+ currents found in these cells.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 5
    ISSN: 1432-2013
    Keywords: Bone cell ; Chloride conductance ; Potassium conductance ; Inwardly rectifying K+ channel ; Outwardly rectifying Cl− channel
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Membrane electrical properties of freshly isolated rat osteoclasts were studied using patch-clamp recording methods. Characterization of the passive membrane properties indicated that the osteoclast cell membrane behaved as an isopotential surface. The specific membrane capacitance was 1.2±0.3 μF/cm2 (mean ±SD), with no difference between cells plated on glass and those adhering to a permeable collagen substrate. The current/voltage (I/V) relationship of all cells showed inward rectification and I/V curves shifted 51 mV positive per tenfold increase of [K+]out, indicating an inwardly rectifying K+ conductance. The voltage dependence of the K+ chord conductance (g K) also shifted positive along the voltage axis, and the maximum conductance increased, with elevation of [K+]out. g K for cells bathed in 4.7 mM [K+]out increased e-fold per 12mV hyperpolarization, and half-maximal activation was at −89 mV. Approximately 18% (50 pS/pF) of the maximum g K was active at −70 mV. Inward single-channel currents were recorded in cell-attached patches at hyperpolarizing potentials. With symmetrical K+, channel conductance was 25±3 pS and reversal was close to the K+ equilibrium potential, consistent with this K+ channel underlying the whole-cell K+ currents. With both conventional whole-cell and perforated-patch recording, no voltage-activated Ca2+ current was detected. In approximately 30% of osteoclasts studied, an outwardly rectifying current was observed, which was reversibly blocked by 4,4′-diisothiocyanostilbene-2,2′-disulphonic acid (DIDS) and 4-acetamido-4′-isothiocyanostilbene2,2′-disulphonic acid (SITS). This DIDS- and SITS-sensitive current reversed direction at the chloride equilibrium potential. We conclude that an inwardly rectifying K+ current is present in all rat osteoclasts and that some osteoclasts also exhibit an outwardly rectifying Cl− current. Both these membrane conductances may play an important physiological role by dissipating the potential that arises from the electrogenic transport of H+ across the ruffled membrane of the osteoclast.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...