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J Physiol Volume 525, Number 2, 307-317, June 1, 2000
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The Journal of Physiology (2000), 525.2, pp. 307-317
© Copyright 2000 The Physiological Society

ATP-sensitive potassium channels in capillaries isolated from guinea-pig heart

Michael Mederos y Schnitzler, Christian Derst, Jürgen Daut and Regina Preisig-Müller

Institut für Normale und Pathologische Physiologie, Universität Marburg, Deutschhausstrasse 2, D-35037 Marburg, Germany

  1. The full-length cDNAs of two different alpha-subunits (Kir6.1 and Kir6.2) and partial cDNAs of three different beta-subunits (SUR1, SUR2A and SUR2B) of ATP-sensitive potassium (KATP) channels of the guinea-pig (gp) were obtained by screening a cDNA library from the ventricle of guinea-pig heart.

  2. Cell-specific reverse-transcriptase PCR with gene-specific intron-spanning primers showed that gpKir6.1, gpKir6.2 and gpSUR2B were expressed in a purified fraction of capillary endothelial cells. In cardiomyocytes, gpKir6.1, gpKir6.2, gpSUR1 and gpSUR2A were detected.

  3. Patch-clamp measurements were carried out in isolated capillary fragments consisting of 3-15 endothelial cells. The membrane capacitance measured in the whole-cell mode was 19·9 ± 1·0 pF and was independent of the length of the capillary fragment, which suggests that the endothelial cells were not electrically coupled under our experimental conditions.

  4. The perforated-patch technique was used to measure the steady-state current-voltage relation of capillary endothelial cells. Application of K+ channel openers (rilmakalim or diazoxide) or metabolic inhibition (250 µM 2,4-dinitrophenol plus 10 mM deoxyglucose) induced a current that reversed near the calculated K+ equilibrium potential.

  5. Rilmakalim (1 µM), diazoxide (300 µM) and metabolic inhibition increased the slope conductance measured at -55 mV by a factor of 9·0 (±1·8), 2·5 (±0·2) and 3·9 (±1·7), respectively. The effects were reversed by glibenclamide (1 µM).

  6. Our results suggest that capillary endothelial cells from guinea-pig heart express KATP channels composed of SUR2B and Kir6.1 and/or Kir6.2 subunits. The hyperpolarization elicited by the opening of KATP channels may lead to an increase in free cytosolic Ca2+, and thus modulate the synthesis of NO and the permeability of the capillary wall.



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