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Pflügers Archiv

, Volume 422, Issue 6, pp 552–557 | Cite as

Thapsigargin discharges intracellular calcium stores and induces transmembrane currents in human endothelial cells

  • Marion Gericke
  • Guy Droogmans
  • Bernd Nilius
Heart, Circulation, Respiration and Blood; Environmental and Exercise Physiology

Abstract

We have measured the effects of thapsigargin, a specific inhibitor of endoplasmic Ca2+-adenosine 5′-triphosphatase (Ca2+-ATPase), on membrane currents and on the intracellular Ca2+ concentration ([Ca2+]i) in single endothelial cells from the human umbilical cord vein. Currents were recorded by means of the patchclamp technique in the whole-cell mode and [Ca2+]i was measured using Fura II. Application of thapsigargin at concentrations between 0.2 and 2 μmol/l induced a slow increase in [Ca2+]i to a peak value of 400±110 nmol/l above a resting level of 120±35 nmol/l, and then slowly declined to a new steady-state level of 315±90 nmol/l (n=33). The thapsigargin-induced increase in [Ca2+]i depended on the extracellular Ca2+ concentration ([Ca2+]o: it declined after removal of extracellular Ca2+, but increased again when [Ca2+]o was augmented, indicating that the response depends on a transmembrane influx of Ca2+ ions. The peak amplitude of the histamine-induced Ca2+ transient was reduced in the presence of thapsigargin. This reduction was more pronounced when histamine was applied at the peak of the increase in [Ca2+]i induced by thapsigargin than during the rising phase of the changes in [Ca2+]i. The decline of the Ca2+ transient induced by histamine after washing out the agonist was also affected by thapsigargin. Before application of thapsigargin, this decline could be described by a single exponential with a time constant τ equal to 24.5±5 s (n=7). In the presence of thapsigargin, the decline was much slower (n =8 cells), although in four cells a fraction of about 23% still exchanged with a similar fast τ value of 29.4±4 s. Thapsigargin also induced a slowly developing inward current in endothelial cells at a holding potential of −40 mV. Voltage ramps applied before and during the development of this current indicated that a non-selective cation channel with a reversal potential near 0 mV was activated. In contrast with the Ca2+ transients, these currents did not show a declining phase. These results indicate that inhibition of the endoplasmic Ca2+ pump in endothelial cells increases [Ca2+]i. The tonic component of this increase might be partly due to opening of non-selective Ca2+-permeable cation channels activated by depletion of intracellular stores.

Key words

Endothelial cells Intracellular calcium Ca2+ stores Thapsigargin Non-selective cation channels 

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Copyright information

© Springer-Verlag 1993

Authors and Affiliations

  • Marion Gericke
    • 1
  • Guy Droogmans
    • 2
  • Bernd Nilius
    • 1
  1. 1.Max Planck GroupMolecular and Cellular PhysiologyLeuvenBelgium
  2. 2.Department of PhysiologyCatholic University LeuvenLeuvenBelgium

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