Abstract
Among other characteristics, the steady-state current-voltage relationship of patch-clamped single atrial myocytes from guinea-pig hearts is defined by an outward current hump in the potential region −15 to +40mV. This hump was reversibly suppressed by Co2+ (3 mM) or nitrendipine (5 μM) and enhanced by Bay K 8644 (5 μM). The maintained outward current component suppressed by Co2+ extended between −15.2±1.9 mV and +39.5 ±1.7 mV (mean±SEM of 14 cells) and has an amplitude of 95.7±9.4 pA at +10 mV. In isochronal I-V curves, the hump was already visible at 400 ms with essentially the same amplitude as at 1500 ms. The Co2+ -sensitive outward current underlying the hump was poorly time-dependent during 1.5 s voltage pulses but slowly relaxed upon repolarization. Tail currents reversed near the K+ equilibrium potential under our experimental conditions. The current hump of the steady-state I-V curve was also abolished by caffeine (10 mM) or ryanodine (3 μM), both drugs that interfere with sarcoplasmic reticulum function. Apamin (1 μM) or quinine (100 μM) but not TEA (5–50 mM) markedly reduced its amplitude. However, at similar concentrations as required to inhibit the hump, both apamin and quinine appeared to be poorly specific for Ca2+ -activated K+ currents in heart cells since they also inhibited the L-Type Ca2+ current. It is concluded that a long lasting Ca2+ -activated outward current, probably mainly carried by K+ ions but not sensitive to TEA, exists in atrial myocytes which is responsible for the current hump of the background I-V curve.
Similar content being viewed by others
References
Ballerman BJ, Brenner BM 1986) Role of atrial peptides in body fluid homeostasis. Circ Res 58:619–630
Barcenas-Ruiz L, Wier WG (1987) Voltage dependence of intracellular [Ca2+]i transients in guinea pig ventricular myocytes. Circ Res 61:148–154
Baró I, Escande D (1989) A Ca2+ -activated K+ current in guinea pig atrial myocytes. Pflügers Arch 414 (Suppl 1):5168
Barrett JN, Magleby KL, Pallotta BS (1982) Properties of single calcium -activated potassium channels in cultured rat muscle. J Physiol (Lond) 331:211–230
Bean BP (1985) Two kinds of calcium channels in canine atrial cells. J Gen Physiol 86:1–30
Bean BP, Sturek M, Puga A, Hermsmeyer K (1987) Nitrendipine block of calcium channels in cardiac and vascular muscle. J Cardiovasc Pharmacol 9: S17-S24
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) 371:45–67
Bkaily G, Sperelakis N, Renaud JF, Payet MD (1985) Apamin, a highly specific Ca2+ blocking agent in heart muscle. Am J Physiol 248:H961-H965
Blatz AL, Magleby KL (1986) Single apamin-blocked Ca-activated K+ channels of small conductance in cultured rat skeletal muscle. Nature 323:718–720
Blatz AL, Magleby KL (1987) Calcium-activated potassium channels. Trends Neurosci 10:463–467
Bourque CW (1988) Transient calcium-dependent potassium current in magnocellular neurosecretory cells of the rat supraoptic nucleus. J Physiol (Lond) 397:331–347
Brown DA, Higashida H (1988) Voltage- and calcium-activated potassium currents in mouse neuroblastoma x rat glioma hybrid cells. J Physiol (Lond) 397:149–165
Callewaert G, Vereecke J, Carmeliet E (1986) Existence of a calcium-dependent potassium channel in the membrane of cow cardiac Purkinje cells. Pflügers Arch 406:424–426
Carmeliet E, Biermans G, Callewaert G, Vereecke J (1987) Potassium currents in cardiac cells. Experientia 43:1175–1184
Cassell JF, McLachlan EM (1987) Two calcium-activated potassium conductances in a subpopulation of coeliac neurones of guineapig and rabbit. J Physiol (Lond) 358:373–394
Coraboeuf E (1980) Voltage clamp studies of the slow inward current. In: Zipes DP, Bailey JC, Elharrar V (eds) The slow inward current and cardiac arrythmias. Nijhoff, Dordrecht, pp 25–95
Coraboeuf E, Carmeliet E (1982) Existence of two transient outward currents in sheep cardiac Purkinje fibers. Pflügers Arch 392: 352–359
Escande D, Loisance D, Planché C, Coraboeuf E (1985) Age-related changes of action potential shape in isolated human atrial fibers. Am J Physiol 249:H843-H850
Escande D, Coulombe A, Faivre JF, Deroubaix E, Coraboeuf E (1987) Two types of transient outward currents in adult human atrial cells. Am J Physiol 252:H142-H148
Gautier P, Escande D, Bertrand JP, Seguin J, Guiraudou P (1989) Electrophysiological effects of penticainide (CM 7857) in isolated human atrial and ventricular fibers. J Cardiovasc Pharmacol 13:328–335
Glavinovic MI, Trifaró JM (1988) Quinine blockade of currents through Ca2+ -activated K+ channels in bovine chromaffin cells. J Physiol (Lond) 399:139–152
Hamill OP, Marty A, Neher E, Sakmann B, Sigworth FJ (1981) Improved patch-clamp techniques for high resolution current recording from cells and cell-free membrane patches. Pflügers Arch 391:85–100
Hess P, Lansman JB, Tsien RW (1984) Different modes of Ca channel gating behaviour favoured by dihydropyridine Ca agonists and antagonists. Nature 311:538–544
Hiraoka M, Kawano S (1987) Mechanism of increased amplitude and duration of the plateau with sudden shortening of diastolic intervals in rabbit ventricular cells. Circ Res 60:14–26
Hugues M, Schmid H, Romey G, Duval D, Frelin C, Lazdunski M (1982) The Ca2+ -dependent slow K+ conductance in cultured rat muscle cells: characterization with apamin. EMBO J 1:1039–1042
Hume JR (1983) Time-dependent outward current in isolated guinea-pig atrial and ventricular myocytes. Biophys J 41:311a
Hume JR, Uehara A (1985) Ionic basis of the different action potential configurations of single guinea-pig atrial and ventricular myocytes. J Physiol (Lond) 368:525–544
Iijima T, Irisawa H, Kameyama M (1985) Membrane currents and their modification by acetylcholine in isolated single atrial cells of the guinea-pig. J Physiol (Lond) 359:485–501
Inoue D, Hachisu M, Pappano AJ (1983) Acetylcholine increases resting membrane potassium conductance in atrial but not in ventricular muscle during muscarinic inhibition of Ca++ -dependent action potentials in chick heart. Circ Res 53:158–167
Isenberg G, Klöckner U (1982a) Calcium tolerant ventricular myocytes prepared by preincubation in a “KB medium”. Pflügers Arch 395:6–18
Isenberg G, Klöckner U (1982b) Calcium currents of isolated bovine ventricular myocytes are fast and of large amplitude. Pflügers Arch 395:30–41
Josephson IR, Sanchez-Chapula J, Brown AM (1984) A comparison of calcium currents in rat and guinea pig single ventricular cells. Circ Res 54:144–156
Kenyon JL, Sutko JL (1987) Calcium- and voltage-activated plateau currents of cardiac Purkinje fibers. J Gen Physiol 89:921–958
Lang DG, Ritchie AK (1987) Large and small conductance calcium-activated potassium channels in the GH3 anterior pituitary cell line. Pflügers Arch 410:614–622
Lipp P, Pott L (1988) Transient inward current in guinea-pig atrial myocytes reflects a change of sodium-calcium exchange current. J Physiol (Lond) 397:601–630
Lipp P, Mechmann S, Pott L (1987) Effects of calcium release from sarcoplasmic reticulum on membrane currents in guinea pig atrial cardioballs. Pflügers Arch 410:121–131
Marban E, Wier WG (1985) Ryanodine as a tool to determine the contributions of calcium entry and calcium release to the calcium transient and contraction of cardiac Purkinje fibers. Circ Res 56:133–138
Maylie J, Morad M (1984) A transient outward current related to calcium release and development of tension in elephant seal atrial fibres. J Physiol (Lond) 357:267–292
Meech RW, Standen NB (1975) Potassium activation in Helix aspersa neurones under voltage clamp: a component mediated by calcium influx. J Physiol (Lond) 249:211–239
Mitra R, Morad M (1985) A uniform method for dissociation of myocytes from hearts and stomachs of vertebrates. Am J Physiol 249:H1056-H1060
Miura Y, Inui J (1984) Multiple effects of alpha-adrenoceptor stimulation on the action potential of rabbit atrium. 325:47–53
Morris AP, Gallacher DV, Irvine RF, Petersen OH (1987) Synergism of inositol trisphosphate and tetrakisphosphate in activating Ca2+ -dependent K+ channels. Nature 330:653–655
Petersen OH (1986) Calcium-activated potassium channels and fluid secretion by exocrine glands. Am J Physiol 251:G1-G13
Schramm M, Thomas G, Toward R, Franckowiak G (1983) Novel dihydropyridines with positive inotropic action through activation of Ca2+ channels. Nature 303:535–537
Siegelbaum SA, Tsien RW, Kass RS (1977) Role of intracellular calcium in the transient outward current of calf Purkinje fibres. Nature 269:611–613
Sutko JL, Thompson LJ, Kort AA, Lakatta EG (1986) Comparison of effects of ryanodine and caffeine on rat ventricular myocardium. Am J Physiol 250:H786-H795
Tseng GN, Robinson RB, Hoffman BF (1988) Passive properties and membrane currents of canine ventricular myocytes. J Gen Physiol 90:671–701
Welsh MJ, McCann JD (1985) Intracellular calcium regulates basolateral potassium channels in chloride-secreting epithelium. Proc Natl Acad Sci USA 82:8823–8826
Woods WT (1984) Effects of elastase and collagenase on microelectrode impalements in canine atria at different ages. J Mol Cell Cardiol 16:843–850
Yue DT, Marban E (1988) A novel cardiac potassium channel that is active and conductive at depolarized potentials. Pflügers Arch 413:127–133
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Baró, I., Escande, D. A long lasting Ca2+ -activated outward current in guinea-pig atrial myocytes. Pflugers Arch. 415, 63–71 (1989). https://doi.org/10.1007/BF00373142
Received:
Revised:
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/BF00373142