Abstract
Tension and patch clamp recording techniques were used to investigate the relaxation of rabbit pulmonary artery and the properties of the K+ current activated by levcromakalim in isolated myocytes. Under whole-cell voltage clamp, holding at −60 mV in symmetrical 139 mm K+, levcromakalim (10 μm) induced a noisy inward current of −116 ± 19 pA (n = 13) which developed over 1 to 2 min. This current could be blocked by either glibenclamide (10 μm) or phencyclidine (5–50 μM) and was unaffected when extracellular Ca2+ was removed. Both these drugs inhibited the levcromakalim-induced relaxation of muscle strips precontracted with 20 mm [K+] o . Application of voltage ramps in symmetrical 139 mm K+ confirmed that the levcromakalim-induced current was carried by K+ ions and was weakly voltage dependent over the potential range from −100 to +40 mV.
The unitary current amplitude and density of the channels underlying the levcromakalim-activated whole-cell K+ current was estimated from the noise in the current record. We estimate that levcromakalim caused activation of around 300 channels per cell, with a single channel current of 1.1 pA, corresponding to a slope conductance of about 19 pS. Furthermore, cells dialyzed with an ATP-free pipette solution developed a large noisy inward current at −60 mV, which could subsequently be blocked by flash photolysis of caged ATP. Analysis of the noise associated with this current indicated that the single channel amplitude underlying the ATP-blocked current was 1.4 pA, a value similar to that estimated for the levcromakalim-induced current. We conclude that the conductance of this ATP-sensitive channel is likely to be small under physiological conditions and that it is present at low density.
Similar content being viewed by others
References
Ashcroft, S.J.H., Ashcroft, F.M. 1990. Properties and function of ATP-sensitive K-channels. Cell. Signal. 2:197–214
Beech, D.J., Zhang, H., Nakao, K., Bolton, T.B. 1993. K channel activation by nucleotide diphosphates and its inhibition by glibenclamide in vascular smooth muscle cells. Br. J. Pharmacol. 110:573–582
Beech, D.J., Bolton, T.B. 1989. Properties of the cromakalim-induced potassium conductance in smooth muscle cells isolated from the rabbit portal vein. Br. J. Pharmacol. 98:851–864
Clapp, L.H., Davey, R., Gurney, A.M. 1993. ATP-sensitive K+ channels mediate the vasodilation produced by lemakalim in rabbit pulmonary artery. Am. J. Physiol. 264:H1907-H1915
Clapp, L.H., Gurney, A.M. 1991. Outward currents in rabbit pulmonary artery cells dissociated with a new technique. Exp. Physiol. 76:677–693
Clapp, L.H., Gurney, A.M. 1992. ATP-sensitive K+ channels regulate the resting potential of pulmonary arterial smooth muscle cells. Am. J. Physiol. 262:H916-H920
Clapp, L.H., Gurney, A.M. 1993. ATP-sensitive K+ channels in the pulmonary vasculature. In: The Role of Ion Flux in Pulmonary Vascular Control. E.K. Weir, J.R. Hume, J.T. Reeves, editors, Plenum, New York
Cook, N.S., Quast, U. 1990. Potassium channel pharmacology. In: Potassium Channels: Structure, Classification, Function and Therapeutic Potential. N.S. Cook, editor, pp. 209–255. Ellis Horwood, Chichester, UK
Dart, C., Standen, N.B. 1993. Adenosine-activated potassium current in smooth muscle cells isolated from the pig coronary artery. J. Physiol. 471:767–786
Daut, J., Maier-Rudolph, W., von Beckerath, N., Mehrke, G., Gunther, K., Goedel-Meinen, L. 1990. Hypoxic vasodilation of coronary arteries is mediated by ATP-sensitive K+ channels. Science 247:1341–1344
Eckman, D.M., Frankovich, J.D., Keef, K.D. 1992. Comparison of the actions of acetylcholine and BRL 38227 in guinea-pig coronary artery. Br. J. Pharmacol. 106:9–16
Evans, M.A., Clapp, L.H., Gurney, A.M. 1993. Photolysis of caged ATP activates a K conductance in rabbit pulmonary myocytes. J. Physiol. (in press)
Fabiato, A. 1991. Buffering: Computer programs and simulations. In: Cellular Calcium, a Practical Approach. J.G. McCormack, P.H. Cobbold, editors, pp. 159–179. Oxford University, New York
Gelband, C.H., Lodge, N.J., van Breemen, C. 1989. A Ca2+-activated K+ channel from rabbit aorta: Modulation by cromakalim. Eur. J. Pharmacol. 167:201–210
Kajioka, S., Kitamura, K., Kuryiama, K. 1991. Guanosine diphosphate activates an adenosine 5′-triphosphate-sensitive K+ channel in the rabbit portal vein. J. Physiol. 444:397–418
Kajioka, S., Oike, M., Kitamura, K. 1990. Nicorandil opens a calcium-dependent potassium channel in smooth muscle cells of the rat portal vein. J. Pharmacol. Exp. Ther. 254:905–913
Klöckner, U., Trieschmann, U., Isenberg, G. 1989. Pharmacological modulation of calcium and potassium channels in isolated vascular smooth muscle cells. Arzneim. Forsch. Drug Res. 39:120–126
Kovacs, R., Nelson, M.T. 1991. ATP-sensitive K+ channels from aortic smooth muscle incorporated into lipid bilayers. Am. J. Physiol. 261:H604-H609
Langton, P.D. 1993. A versatile superfusion system suitable for whole-cell and excised patch clamp experiments. J. Physiol. 467:244P
Langton, P.D., Clapp, L.H., Dart, C., Gurney, A.M., Standen, N.B. 1993a. Whole-cell K+ current activated by lemakalim in isolated myocytes from rabbit pulmonary artery: estimate of unitary conductance and density by noise analysis. J. Physiol. 459:245P
Langton, P.D., Clapp, L.H., Gurney, A.M., Standen, N.B. 1993b. Lemakalim activated KATP channels in isolated myocytes of rabbit pulmonary artery occur at low density and have a small conductance. Biophys. J. 64:A149
Longman, S.D., Hamilton, T.C. 1992. Potassium channel activator drugs: Mechanism of action, pharmacological properties, and therapeutic potential. Med. Res. Rev. 12:73–148
Miyoshi, Y., Nakaya, Y., Wakatsuki, T., Nakaya, S., Fujino, K., Saito, K., Inoue, I. 1992. Endothelin blocks ATP-sensitive K+ channels and depolarizes smooth muscle cells of porcine coronary artery. Circ. Res. 70:612–616
Noack, T., Deitmer, P., Edwards, G., Weston, A.H. 1992a. Characterization of potassium currents modulated by BRL 38227 in rat portal vein. Br. J. Pharmacol. 106:717–726
Noack, T., Edwards, G., Deitmer, P., Weston, A.H. 1992b. Potassium channel modulation in rat portal vein by ATP depletion: a comparison with the effects of levcromakalim (BRL 38227). Br. J. Pharmacol. 107:945–955
Quast, U., Cook, N.S. 1989. Moving together: K+ channel openers and ATP-sensitive K+ channels. Trends Pharmacol. Sci. 10:431–435
Russell, S.N., Smirnov, S.V., Aaronson, P.I. 1992. Effects of BRL 38227 on potassium currents in smooth muscle cells isolated from rabbit portal vein and human mesenteric artery. Br. J. Pharmacol. 105:549–556
Sigworth, F.J. 1980. The variance of sodium current fluctuations at the node of Ranvier. J. Physiol. 307:97–129
Silberberg, S.D., Magleby, K.L. 1993. Preventing errors when estimating single channel properties from the analysis of current fluctuations. Biophys. J. 65:1570–1585
Silberberg, S.D., van Breemen, C. 1992. A potassium current activated by lemakalim and metabolic inhibition in rabbit mesenteric artery. Pfluegers Arch. 420:118–120
Standen, N.B., Quayle, J.M., Davies, N.W., Brayden, J.E., Huang, Y., Nelson, M.T. 1989. Hyperpolarizing vasodilators activate ATP-sensitive K+ channels in arterial smooth muscle. Science 245:177–180
Author information
Authors and Affiliations
Additional information
We thank SmithKline & Beecham for the gift of levcromakalim, ICI Pharmaceuticals for the gift of charybdotoxin and Prof. D. Colquhoun for the noise analysis programs. We also thank Mr. R. Davey for technical assistance with tension experiments. This work was supported by the British Heart Foundation and the Wellcome Trust. L.H.C. is a Wellcome Research Fellow and P.L. is an intermediate fellow of the BHF.
Rights and permissions
About this article
Cite this article
Clapp, L.H., Gurney, A.M., Standen, N.B. et al. Properties of the ATP-sensitive K+ current activated by levcromakalim in isolated pulmonary arterial myocytes. J. Membarin Biol. 140, 205–213 (1994). https://doi.org/10.1007/BF00233709
Received:
Revised:
Issue Date:
DOI: https://doi.org/10.1007/BF00233709