Divalent ion block of inward rectifier current in human capillary endothelial cells and effects on resting membrane potential

Authors


Corresponding author R. Numann: Wyeth-Ayerst Research, CN 8000, Princeton, NJ 08543, USA. Email: NumannR@War.Wyeth.Com

Abstract

  • 1Cultured human capillary endothelial cells (HCEC) contain a large inward rectifier current, IK(IR), that can be abolished by removing external K+ or by adding 50 μm Ba2+.
  • 2We show that IK(IR) is responsible for maintaining the hyperpolarized potential (−60.6 ± 0.5 mV, n= 83) of HCEC. Blocking IK(IR) with 50 μm Ba2+ shifts the zero current level and depolarizes HCEC by 36.5 ± 1.3 mV (n= 4).
  • 3Increasing external Ca2+ concentration ([Ca2+]o) from 0.5 to 7 mm reduces the magnitude of IK(IR) by 36.5 ± 2.3 % (n= 5) and depolarizes the cells by 10.33 ± 2.4 mV (n= 3), whereas decreasing [Ca2+]o from 1.8 to 0.5 mm increases the amplitude of IK(IR) by 6.9 ± 1.9 % (n= 4). The relationship between [Ca2+]o and the percentage block of IK(IR) gives a Kd value of 5.4 ± 0.6 mm at −120 mV.
  • 4I K(IR) is also blocked by other divalent ions, with Ba2+ >> Sr2+ > Mg2+ > Mn2+= Ca2+, and the block of peak current at −120 mV being 85.3 ± 3.2 % (n= 5) for 50 μm Ba2+, 62.9 ± 2.2 % (n= 5) for 5 mm Sr2+, 40.7 ± 2.5 % (n= 9) for 5 mm Mg2+, 33.4 ± 2.1 % (n= 5) for 5 mm Mn2+ and 32.9 ± 2.1 % (n= 5) for 5 mm Ca2+.
  • 5The voltage dependence of Sr2+ block of peak IK(IR) occurred with a Kd value of 1.0 ± 0.09 mm for −140 mV, 1.9 ± 0.16 mm for −130 mV, 3.1 ± 0.28 mm for −120 mV, 4.6 ± 0.34 mm for −110 mV and 6.4 ± 0.5 mm for −100 mV (n= 5), with a calculated electrical distance (δ) of 0.44 from the outside.

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