Pflügers Archiv

, Volume 427, Issue 1–2, pp 9–16 | Cite as

Large conductance calcium-activated potassium channels in cultured retinal pericytes under normal and high-glucose conditions

  • Susanne Berweck
  • Albrecht Lepple-Wienhues
  • Matthias Stöß
  • Michael Wiederholt
Heart, Circulation, Respiration and Blood; Environmental and Exercise Physiology


Pericytes are considered to contribute to the regulation of retinal microcirculation which is impaired in diabetic retinopathy. Single, large-conductance, Ca2+-dependent K+ channels (BK) were studied in cultured bovine retinal capillary pericytes using the patch-clamp method. In excised patches with symmetrical 135-mmol/l K+ solutions a single channel conductance of 238±9.9 pS was measured. With a K+ gradient of 4/ 135 mmol/l (extracellular/intracellular) the slope conductance averaged 148±2.9 pS at 0 mV. The mean permeability was 4.2×10−13 cm3/s. The channel was highly selective for K+ with a permeability ratio for K+ over Na+ of 1/0.02. The mean open time and the open probability (Po) of the BK channel increased with depolarization and with increasing internal [Ca2+] showing a maximal sensitivity to Ca2+ between 10−4 and 10−5 mol/l Ca2+. Ba2+ (5 mmol/l), quinine (5 mmol/l), and verapamil (Michaelis constant 1.5×10−5 mol/l) blocked from the intracellular side. Tetraethylammonium induced a dose-dependent block from the outside only with a halfmaximal blocking concentration of 2.5×10−4 mol/l. Charybdotoxin (10−8 mol/l) blocked completely from the extracellular side. The channel activity was not changed by either internal adenosine triphosphate (ATP, 10−4 mol/l) or the putative opener of ATP-sensitive K+ channels Hoe 234 (10−6 mol/l). In cell-attached patches channelPo was less than 3%. After a 3-day incubation in culture medium containing an elevated glucose concentration (22.5 mmol/l) the channel activity in attached patches was markedly increased. These data indicate that cultured retinal pericytes possess a BK channel. The activity of the channel increases after incubation with elevated glucose concentrations, which could indicate altered regulation of the channel under these conditions. The implications of altered function of BK channels are discussed with respect to haemodynamic changes observed in diabetic retinopathy.

Key words

Pericytes Smooth muscle cells Ca2+dependent K+ channel Patch-clamp technique Diabetic retinopathy/microangiopathy Vasodilation 


Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.


  1. 1.
    Asano M, Masuzawa-Ito K, Matsuda T (1993) Charybdotoxin-sensitive K+ channels regulate the myogenic tone in the resting state of arteries from spontaneously hypertensive rats. Br J Pharmacol 108:214–222Google Scholar
  2. 2.
    Benham CD, Bolton TB, Lang RJ, Takewaki T (1986) Calcium-activated potassium channels in single smooth muscle cells of rabbit jejunum and guinea-pig mesenteric artery. J Physiol (Lond) 371:45–67Google Scholar
  3. 3.
    Berweck S, Thieme H, Helbig H, Lepple-Wienhues A, Wiederholt M (1993) Effect of elevated glucose concentration on membrane voltage regulation in retinal capillary pericytes. Diabetes 42:1347–1350Google Scholar
  4. 4.
    Berweck S, Thieme H, Lepple-Wienhues A, Helbig H, Wiederholt M (1993) Insulin-induced hyperpolarization in retinal capillary pericytes. Invest Ophthalmol Vis Sci 34:3402–3407Google Scholar
  5. 5.
    Brayden JE, Nelson MT (1992) Regulation of arterial tone by activation of calcium-dependent potassium channels. Science 256:532–535Google Scholar
  6. 6.
    Buchanan RA, Wagner RC (1990) Morphometric changes in pericyte-capillary endothelial cell associations correlated with vasoactive stimulus. Microcirc Endothelium Lymphatics 6:159–181Google Scholar
  7. 7.
    Colquhoun D, Sigworth FJ (1983) Fitting and statistical analysis of single channel records. In: Sakman B, Neher E (eds) Single channel recording. Plenum, New York, pp 191–263Google Scholar
  8. 8.
    Cringle SJ, Yu DY, Alder VA, Su EN (1993) Retinal blood flow by hydrogen clearance polarography in the streptozotocin-induced diabetic rat. Invest Ophthalmol Vis Sci 34:1716–1721Google Scholar
  9. 9.
    Dowd TL, Gupta RK (1993) NMR studies of the effect of hyperglycemia on intracellular cations in rat kidney. J. Biol Chem 268:991–996Google Scholar
  10. 10.
    Groschner K, Silberberg SD, Gelband CH, Breemen C van (1991) Ca2+-activated K+ channels in airway smooth muscle are inhibited by cytoplasmic adenosine triphosphate. Pflügers Arch 417:517–522Google Scholar
  11. 11.
    Granwald JE, Riva CE, Bracker AJ, Sinclair SH, Petrig BL (1984) Altered retinal vascular response to 100% oxygen breathing in diabetes mellitus. Ophthalmology 91:1447–1452Google Scholar
  12. 12.
    Hamill OP, Marty A, Neher E, Sakman B, Sigworth FJ (1981) Improved patch-clamp techniques for high-resolution current recording from cells and cell-free membrane patches. Pflügers Arch 391:85–100Google Scholar
  13. 13.
    Helbig H, Kornacker S, Berweck S, Stahl F, Lepple-Wienhues SSA, Wiederholt M (1992) Membrane potentials in retinal capillary pericytes: excitability and effect of vasoactive substances. Invest Ophthalmol Vis Sci 33:2105–2112Google Scholar
  14. 14.
    Herman IM, D'Amore PA (1985) Microvascular pericytes contain muscle and nonmuscle actins. J Cell Biol 101:43–52Google Scholar
  15. 15.
    Hirsch J, Leipziger J, Fröbe U, Schlatter E (1993) Regulation and possible physiological role of the Ca2+-dependent K+ channel of cortical collecting ducts of the rat. Pflügers Arch 422:492–498Google Scholar
  16. 16.
    Hodgkin AL, Katz B (1949) The effect of sodium ions on the electrical activity of the giant axon of the squid. J Physiol (Lond) 108:37–77Google Scholar
  17. 17.
    Inoue R, Kitamura K, Kuriyama H (1985) Two Ca-dependent K-channels classified by the application of tetraethylammonium distribute to smooth muscle membranes of the rabbit portal vein. Pflügers Arch 405:173–179Google Scholar
  18. 18.
    Kelley C, D'Amore PA, Hechtman HB, Shepro D (1988) Vasoactive hormones and cAMP affect pericyte contraction and stress fibres in vitro. J Muscle Res Cell Motil 9:184–194Google Scholar
  19. 19.
    Klöckner U, Isenberg G (1992) ATP supresses activity of Ca2+-activated K+ channels by Ca2+ chelation. Pflügers Arch 420:101–105Google Scholar
  20. 20.
    Kolb HA (1990) Potassium channels in excitable and nonexcitable cells. Rev Physiol Biochem Pharmacol 115:51–91Google Scholar
  21. 21.
    Latorre R, Oberhauser A, Iabarca P, Alvarez O (1989) Varieties of calcium-activated potassium channels. Annu Rev Physiol 51:385–399Google Scholar
  22. 22.
    Marty A (1983) Blocking of the large unitary calcium-dependent potassium currents by internal sodium ions. Pflügers Arch 396:179–181Google Scholar
  23. 23.
    Miller C, Moczydlowski E, Latorre R, Phillips M (1985) Charybdotoxin, a protein inhibitor of single Ca2+-activated K+ channels from mammalian skeletal muscle. Nature 313:316–318Google Scholar
  24. 24.
    Nakagawa M, Kobayashi S, Kimura I, Kimura M (1989) Diabetic state-induced modification of Ca, Mg, Fe and Zn content of skeletal, cardiac and smooth muscles. Endocrinol Jpn 36:795–807Google Scholar
  25. 25.
    Ohara T, Sussman KE, Draznin B (1991) Effect of diabetes on cytosolic free Ca2+ and Na+-K+-ATPase in rat aorta. Diabetes 40:1560–1563Google Scholar
  26. 26.
    Pavenstädt H, Lindemann S, Lindemann V, Späth M, Kunzelmann K, Greger R (1991) Potassium conductance of smooth muscle cells from rabbit aorta in primary culture. Pflügers Arch 419:57–68Google Scholar
  27. 27.
    Qi J, Curley RM, Belis JA (1992) Cytosol-free calcium concentration in single bladder smooth muscle cells from normal and diabetic rats. Pharmacology 45:90–98Google Scholar
  28. 28.
    Resnick LM (1989) Hypertension and abnormal glucose homeostasis. Possible role of divalent ion metabolism. Am J Med 87 (6A):17S-22SGoogle Scholar
  29. 29.
    Schaffer SW, Mozaffari MS, Artman M, Wilson GL (1989) Basis for myocardial mechanical effects associated with noninsulin dependent diabetes. Am J Physiol 256:E25-E30Google Scholar
  30. 30.
    Sims DE (1991) Recent advances in pericyte biology — implications for health and disease. Can J Cardiol 7:431–443Google Scholar
  31. 31.
    Singer JJ, Walsh JV (1987) Characterization of calcium activated potassium channels in single smooth muscle cells using the patch-clamp technique. Pflügers Arch 408:98–111Google Scholar
  32. 32.
    Tilton RG, Kilo C, Williamson JR (1979) Pericyte-endothelial relationships in cardiac and skeletal muscle capillaries. Microvase Res 18:325–335Google Scholar
  33. 33.
    Tilton RG, Hoffmann PL, Kilo C, Williamson JR (1987) Pericyte degeneration and basement membrane thickening in skeletal muscle capillaries of human diabetics. Diabetes 30:326–334Google Scholar
  34. 34.
    Weston AH, Edwards G (1992) Recent progress in potassium channel opener pharmacology. Biochem Pharmacol 43:47–54Google Scholar
  35. 35.
    Zimmermann K (1923) Der feinere Bau der Blutcapillaren. Z Anat Entwickl 68:29–109Google Scholar

Copyright information

© Springer-Verlag 1994

Authors and Affiliations

  • Susanne Berweck
    • 1
  • Albrecht Lepple-Wienhues
    • 1
  • Matthias Stöß
    • 1
  • Michael Wiederholt
    • 1
  1. 1.Institut für Klinische Physiologie, Klinikum SteglitzFreie Universität BerlinBerlinGermany

Personalised recommendations