Abstract
In small preparations of rabbit sinoatrial node voltage clamp experiments with the two microelectrode technique were carried out. The effects of extracellular barium ions on the slow inward current and outward currents were studied and the following results were obtained:
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1.
Ba increased the amplitude of the slow inward current without a change in the time course of inactivation. In 10 mM Ba the steady-state inactivation curve (f∞) shifted in the positive direction (3–4 m V), suggesting a neutralization of negative surface charges. A similar shift of the steady state activation curve (d∞) could not be detected.
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2.
Ba reduced the amplitude of the time-dependent (IK, Ix) and time-independent (Ibg) potassium currents in a concentration-dependent manner.
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3.
The block of the time-dependent potassium current, IK, depended on the membrane potential. The block was stronger at negative than at positive potentials. The block could be relieved by depolarizing pulses, the degree of unblock increased with longer duration of the depolarizing pulse.
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4.
Ba blocked the slow outward current Ix in a voltage- and time-dependent manner. Like for IK, the block of Ix was stronger at negative than at positive potentials. A given concentration of Ba produced stronger block of Ix than of IK and the removal of block of Ix by depolarizing pulses was slower than the removal of IK block.
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5.
The effects of Ba on Ix suggest that this current is a potassium current.
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References
Antoni H, Oberdisse E (1965) Elektrophysiologische Untersuchungen über die Barium-induzierte Schrittmacher-Aktivität im isolierten Säugetiermyokard. Pflügers Arch 284:259–272
Armstrong CM, Taylor SR (1980) Interaction of barium ions with potassium channels in squid giant axons. Biophys J 30:473–488
Bassingthwaighte JB, Reuter H (1972) Calcium movements and excitation-contraction coupling in cardiac cells. In: De Mello WC (ed) Electrical phenomena in the heart. Academic Press, New York, pp 353–395
Brown AM, Akaike N, Tsuda Y, Morimoto K (1980) Ion migration and inactivation in the calcium channel. J Physiol (Paris) 76:395–402
DiFrancesco D, McNaughton PA (1980) The effects of calcium on outward membrane currents in cardiac Purkinje fibre. J Physiol 289:347–373
DiFrancesco D, Noma A, Trautwein W (1979) Kinetics and magnitude of the time-dependent potassium current in the rabbit sinoatrial node. Pflügers Arch 381:271–279
Eaton DC, Brodwick MS (1980) Effects of barium on the potassium conductance of squid giant axon. J Gen Physiol 75:727–750
Gilbert DL, Ehrenstein G (1969) Effect of divalent cations on potassium conductance of squid axons. Biophys J 9:447–463
Hermsmeyer K, Sperelakis N (1970) Decrease in K+ conductance and depolarization of frog cardiac muscle produced by Ba2+. Am J Physiol 219:1108–1114
Hille B, Woodhull AM, Shapiro BI (1975) Negative surface charge near sodium channels of nerve: divalent ions, monovalent ions, and pH. Phil. Trans R Soc (Lond) B 270:301–318
Hiraoka M, Ikeda K, Sano T (1980) The mechanism of barium-induced automaticity in ventricular muscle fibers. In: Tadjuddin M, Das PK, Tariq M, Dhalla NS (eds) Advances im myocardiology, vol 1. University Park Press, Baltimore, pp 255–266
Kohlhardt M, Haastert HP, Krause H (1973) Evidence of non-specificity of the Ca channel in mammalian myocardial fibre membranes. Pflügers Arch 342:125–136
Kohlhardt M, Krause H, Kübler M, Herdey A (1975) Kinetics of inactivation and recovery of the slow inward current in the mammalian ventricular myocardium. Pflügers Arch 355:1–17
McDonald TF, Trautwein W (1978) The potassium current underlying delayed rectification in cat ventricular muscle. J Physiol 274:217–247
McLaughlin SGA (1977) Electrostatic potentials at membrane-solution interfaces. In: Bonner F, Kleinzeller A (eds) Current topics in membranes and transport, vol 9. Academic Press, New York
Morimoto K, Campbell D, Tsuda Y, Wilson D, Akaike N, Brown A (1981) Actions of calcium on activation of the Ca channel and current flow through it. Biophys J 33:144a
Noble D, Tsien RW (1969) Outward membrane currents activated in the plateau range of potentials in cardiac Purkinje fibers. J Physiol (Lond) 200:205–231
Noma A, Irisawa H (1976a) Membrane currents in the rabbit sino-atrial node cell as studied by the double micro-electrode method. Pflügers Arch 364:45–52
Noma A, Irisawa H (1976b) A time- and voltage-dependent potassium current in the rabbit sinoatrial node cell. Pflügers Arch 366:251–258
Noma A, Irisawa H (1977) Inward current of the rabbit sinoatrial node cell. Pflügers Arch 372:43–51
Noma A, Trautwein W (1978) Relaxation of the ACh-induced potassium current in the rabbit sinoatrial node cell. Pflügers Arch 377:193–200
Noma A, Kotake H, Irisawa H (1980) Slow inward current and its role mediating the chronotropic effect of epinephrine in the rabbit sinus node. Pflügers Arch 388:1–9
Ohmori H, Yoshida S, Hagiwara S (1981) Single K+ channel currents of anomalous rectification in cultured rat myotubes. Proc Natl Acad Sci USA 78:4960–4964
Osterrieder W, Yang Q-F, Trautwein W (1982) Conductance of the slow inward channel in the rabbit sinoatrial node. Pflügers Arch 394: 85–89
Reid JA, Hecht HH (1967) Barium-induced automaticity in right ventricular muscle in the dog. Circ Res 21:849–856
Reuter H, Scholz H (1977) A study of the ion selectivity and the kinetic properties of the calcium dependent slow inward current in mammalian cardiac muscle. J Physiol 264:17–47
Shibata J (1973) The effects of barium on the action potential and the membrane current of sheep heart Purkinje fibers. J Pharmacol Exp Ther 185:418–426
Standen NB, Stanfield PR (1978) A potential- and time-dependent blockade of inward rectification in frog skeletal muscle fibres by barium and strontium ions. J Physiol 280:160–191
Yanagihara K, Irisawa H (1980) Inward current activated during hyperpolarization in the rabbit sinoatrial node cell. Pflügers Arch 385:11–19
Yanagihara K, Irisawa H (1980) Potassium current during the pacemaker depolarization in rabbit sinoatrial node cell. Pflügers Arch 388:255–260
Yanagihara K, Noma A, Irisawa H (1980) Reconstruction of sino-atrial node pacemaker potential based on the voltage clamp experiments. Jpn J Physiol 30:841–857
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This work was supported by the Deutsche Forschungsgemeinschaft SFB 38, Membranforschung, Project G
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Osterrieder, W., Yang, Q.F. & Trautwein, W. Effects of barium on the membrane currents in the rabbit S-A node. Pflugers Arch. 394, 78–84 (1982). https://doi.org/10.1007/BF01108311
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DOI: https://doi.org/10.1007/BF01108311