Abstract
Small preparations of spontaneously beating rabbit sino-atrial node (SA node) were voltage clamped with the two-microelectrode technique. The effects of 0.25–5 mM Cs+ on the spontaneous pacing rate and the time-dependent inward “pacemaker” current,i h, were studied. In the presence of 2 mM Cs+, the spontaneous pacing rate decreased only slightly even thoughi h was strongly depressed at potentials negative to −60 mV Cs+ had little or no effect on other time-dependent currents observed with clamp pulses less negative than −50 mV. Since no voltage-dependence to the Cs+ effect oni h could be measured (between −90 mV and −20 mV), it was considered unlikely that the lack of Cs+ effect on the rate of diastolic depolarization results from a voltage-dependent effect of Cs+ on thei h channel.
Adrenaline produced a marked positive chronotropic effect in Cs+-treated SA node cells. This effect was accompanied by marked enhancement of the slow inward current (i si) with no change in the Cs+-blockedi h current. These results are consistent with the idea thati h plays a minor role in generation of pacemaker depolarization, and suggest a more prominent role ofi si in the generation of diastolic depolarization in SA nodal cells.
Similar content being viewed by others
References
Brown HF, DiFrancesco D (1980) Voltage-clamp investigations of membrane currents underlying pace-maker activity in rabbit sinoatrial node. J Physiol (Lond) 308:331–151
Brown HF, DiFrancesco D, Noble SJ (1979) How does adrenaline accelerate the heart? Nature 290:31–32
Brown HF, DiFrancesco D, Kimura J, Noble S (1981) Caesium: a useful tool for investigating sino-atrial (S-A) nodes pacemaking. J Physiol (Lond) 317:54P
Cleemann L, Morad M (1979) Potassium currents in frog ventricular muscle: Evidence from voltage clamp currents and extracellular K accumulation. J Physiol (Lond) 286:113–143
DiFrancesco D (1981a) A new interpretation of the pace-maker current in calf Purkinje fibres. J Physiol (Lond) 314:359–378
DiFrancesco D (1981b) A study of the ionic nature of the pace-maker current in calf Purkinic fibres. J Physiol (Lond) 314:377–393
DiFrancesco D (1982) Block and activation of the pace-maker channel in calf Purkinje fibres: Effects of potassium, caesium and rubidium. J Physiol (Lond) 329:485–507
DiFrancesco D, Ojeda C (1980) Properties of the currenti f in the sinoatrial node of the rabbit compared with those of the currenti k2 in the Purkinje fibres. J Physiol (Lond) 308:353–367
DiFrancesco D, Noma A, Trautwein W (1979) Kinetics and magnitude of the time-dependent potassium current in the rabbit sinoatrial node. Pflügers Archiv 381:271–279
Gay LA, Stanfield PR (1977) Cs+ causes a voltage-dependent block of inward K currents in resting skeletal muscle fibres. Nature 267:169–170
Hagiwara S, Miyazaki S, Rosenthal NP (1976) Potassium current and the effect of cesium on this current during anomalous rectification of the egg cell membrane of a starfish. J Gen Physiol 67:621–638
Kokubun S, Nishimura M, Noma A, Irisawa H (1982) Membrane currents in the rabbit atrioventricular node cell. Pflügers Archiv 393:15–22
Kreitner D (1981) Existence of two distinct kinds of pacemaker cells in isolated pieces of the rabbit sinus node. J Physiol (Lond) 312:37–38P
Maylie J, Morad M (1981) Ionic characterization of pacemaker current in voltage clamped rabbit SA node. Biophys J 33:11a
Maylie J, Morad M, Weiss J (1981) A study of pace-maker potential in rabbit sino-atrial node: Measurement of potassium activity under voltage-clamp conditions. J Physiol (Lond) 311:161–178
Noma A, Irisawa H (1976a) Membrane currents in the rabbit sinoatrial node cell as studied by the double microelectrode method. Pflügers Archiv 364:45–52
Noma A, Irisawa H (1976b) A time-and voltage-dependent potassium current in the rabbit sinoatrial node cell. Pflügers Archiv 366:251–258
Noma A, Kotake H, Irisawa H (1980) Slow inward current and ist role mediating the chronotropic effect of epinephrine in the rabbit sinoatrial node. Pflügers Archiv 388:1–9
Noma A, Irisawa H, Kokubun S, Kotake H, Nishimura M, Watanabe Y (1980) Slow current systems in the A-V node of the rabbit heart. Nature 285:228–229
Seyama I (1979) Characteristics of the anion channel in the sinoatrial node of the rabbit. J Physiol (Lond) 294:447–460
Seyama I (1976) Characteristics of the rectifying properties of the sinoatrial node cell of the rabbit. J Physiol (Lond) 255:379–397
Standen NB, Stanfield PR (1978) A potential-and time-dependent blockade of inwart rectification in frog skeletal muscle fibres by barium and strontium ions. J Physiol (Lond) 280:169–191
Vereecke J, Isenberg G, Carmeliet E (1980) K efflux through inward rectifying K channels in voltage clamped Purkinje fibers. Pflügers Archiv 384:207–217
Yanagihara K, Irisawa H (1980a) Inward current activated during hyperpolarization in the rabbit sinoatrial node cell. Pflügers Archiv 385:11–19
Yanagihara K, Irisawa H (1980b) Potassium current during the pacemaker depolarization in rabbit sinoatrial node cell. Pflügers Archiv 388:255–260
Yanagihara K, Noma A, Irisawa H (1980) Reconstruction of the sionatrial node pacemaker potential based on the voltage clamp experiment. Jpn J Physiol 30:841–857
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Noma, A., Morad, M. & Irisawa, H. Does the “pacemaker current” generate the diastolic depolarization in the rabbit SA node cells?. Pflugers Arch. 397, 190–194 (1983). https://doi.org/10.1007/BF00584356
Received:
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/BF00584356