Stimulation of large-conductance Ca2+-activated K+ channels by Evans blue in cultured endothelial cells of human umbilical veins

Biochem Biophys Res Commun. 1999 Jan 27;254(3):666-74. doi: 10.1006/bbrc.1998.0120.


The effect of Evans blue (EB) on large-conductance Ca2+-activated K+ (BKCa) channels was investigated in cultured endothelial cells of human umbilical veins. In whole-cell configuration, EB (50 microM) reversibly increased the amplitude of K+ outward currents (IK). When the patch pipettes were filled with 10 mM EGTA, its stimulatory effect on IK was unaltered. Further application of EB in the presence of suramin, a blocker of P2-purinergic receptor, or AOPCP, an inhibitor of 5'-nucleotidase, still increased IK. However, charybdotoxin (100 nM) suppressed EB-induced increase in IK. In inside-out configuration, bath application of EB (50 microM) did not change single channel conductance but significantly increased the activity of BKCa channels. The EB-induced increase in the activity of BKCa channels was independent on internal Ca2+. EB (50 microM) shifted the activation curve of BKCa channels to less positive membrane potentials by approximately 20 mV. The change in the kinetic behavior of BKCa channels caused by EB in these cells is due to an increase in mean open time and a decrease in mean closed time. These results indicate that EB can stimulate the activity of BKCa channel in endothelial cells. This effect is unrelated to its blockade of P2-purinergic receptors or inhibition of 5'-nucleotidase. The direct stimulation of these ionic channels by EB may contribute to its effect on capillary permeability.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenosine Diphosphate / analogs & derivatives
  • Adenosine Diphosphate / pharmacology
  • Capillary Permeability
  • Cells, Cultured
  • Endothelium, Vascular / cytology
  • Endothelium, Vascular / drug effects*
  • Endothelium, Vascular / physiology
  • Evans Blue / pharmacology*
  • Humans
  • Kinetics
  • Large-Conductance Calcium-Activated Potassium Channels
  • Membrane Potentials
  • Patch-Clamp Techniques
  • Potassium Channels / drug effects*
  • Potassium Channels / physiology
  • Potassium Channels, Calcium-Activated*
  • Suramin / pharmacology
  • Umbilical Veins / cytology
  • Umbilical Veins / drug effects*
  • Umbilical Veins / physiology


  • Large-Conductance Calcium-Activated Potassium Channels
  • Potassium Channels
  • Potassium Channels, Calcium-Activated
  • alpha,beta-methyleneadenosine 5'-diphosphate
  • Evans Blue
  • Suramin
  • Adenosine Diphosphate