BACKGROUND CONDUCTANCE ATTRIBUTABLE TO SPONTANEOUS OPENING OF MUSCARINIC K+ CHANNELS IN RABBIT SINOATRIAL NODE CELLS

被引:0
作者
ITO, H [1 ]
ONO, K [1 ]
NOMA, A [1 ]
机构
[1] KYOTO UNIV,FAC MED,DEPT PHYSIOL,KYOTO 60601,JAPAN
来源
JOURNAL OF PHYSIOLOGY-LONDON | 1994年 / 476卷 / 01期
关键词
D O I
暂无
中图分类号
Q189 [神经科学];
学科分类号
071006 ;
摘要
1. Single myocytes were dissociated from the rabbit sino-atrial node, and the membrane background conductance produced by spontaneous opening of the muscarinic K+ channels was investigated by recording whole-cell and single channel currents in both normal K+ (5.4 mM) and high-K+ (145 mM) external solutions. 2. Increasing external K+ concentration ([K+](o)) from 5.4 to 145 mM induced a large inward shift of the whole-cell current accompanied by considerable current fluctuations at -50 mV. The high-K+-induced current was both K+ selective and voltage dependent, which was examined by varying [K+](o). This current was almost completely suppressed by 1-5 mM Ba2+ or 2-10 mM Cs+ and it was partly blocked by 10 mu M atropine. 3. In high-K+ (l45 mM) solution, 20 nM acetylcholine (ACh) further increased the K+ conductance as well as the current noise. The power density spectrum of the noise was fitted with a sum of two Lorentzian functions. The corner frequencies of both the slow (similar to 5 Hz) and fast (similar to 120 Hz) components were comparable between the noise before and during the ACh application. 4. Internal dialysis with a non-hydrolysable derivative of ATP, 5'-adenylylimidodiphosphate (AMP-PNP) or Mg2+-free solution markedly decreased both the amplitude and fluctuations of the high-K+-induced current. The relation between the variance of the current fluctuations and the mean current amplitude was linear in every experiment using dialysis of AMP-PNP or Mg2+-free internal solution, or using superfusion of ACh. The slopes of these relations gave comparable single channel current amplitudes of -0.7 pA at -50 mV. These results indicate that the spontaneous opening of the muscarinic K+ channels is largely responsible for the high-K+-induced current. 5. In the high-K+ solution, the variance-mean relation at -50 mV showed that the muscarinic K+ channel provides an inward current of 3.12 +/- 2.13 pA pF(-1) (n = 23), which was about 60 % of the total inward background current. 6. In the normal K+ solution, the variance-mean relation at -50 mV indicated that an outward current of 6.0 +/- 2.0 pA (0.33 +/- 0.28 pA pF(-1), n = 8) was provided by the K+ channel. The single channel current amplitude was estimated to be 0.06 +/- 0.02 pA (n = 9). 7. Cell-attached recordings in the absence of ACh demonstrated sporadic and brief openings of channels identical to the ACh-induced channels. The power density spectra of the single channel currents exhibited kinetic properties comparable with those of the whole-cell currents. No obvious channel activities were attributable to K+ channels other than the muscarinic K+ channel in 105 experiments. 8. These results suggest that the K+-selective component of the background current in sinoatrial node cells is entirely due to the spontaneous opening of the muscarinic K+ channels and may play an important role in determining the heart rate under physiological conditions.
引用
收藏
页码:55 / 68
页数:14
相关论文
共 32 条
[1]   RABBIT SINOATRIAL NODE CELLS - ISOLATION AND ELECTROPHYSIOLOGICAL PROPERTIES [J].
DENYER, JC ;
BROWN, HF .
JOURNAL OF PHYSIOLOGY-LONDON, 1990, 428 :405-+
[2]   PROPERTIES OF THE HYPERPOLARIZING-ACTIVATED CURRENT (IF) IN CELLS ISOLATED FROM THE RABBIT SINOATRIAL NODE [J].
DIFRANCESCO, D ;
FERRONI, A ;
MAZZANTI, M ;
TROMBA, C .
JOURNAL OF PHYSIOLOGY-LONDON, 1986, 377 :61-88
[3]  
FABIATO A, 1979, J PHYSIOL-PARIS, V75, P463
[4]   CONTROL OF THE HYPERPOLARIZATION-ACTIVATED CATION CURRENT BY EXTERNAL ANIONS IN RABBIT SINOATRIAL NODE CELLS [J].
FRACE, AM ;
MARUOKA, F ;
NOMA, A .
JOURNAL OF PHYSIOLOGY-LONDON, 1992, 453 :307-318
[5]  
FRACE AM, 1992, PFLUG ARCH EUR J PHY, V421, P97
[6]   A TRANSIENT OUTWARD CURRENT IN ISOLATED CELLS FROM THE CRISTA TERMINALIS OF RABBIT HEART [J].
GILES, WR ;
VANGINNEKEN, ACG .
JOURNAL OF PHYSIOLOGY-LONDON, 1985, 368 (NOV) :243-&
[7]   BACKGROUND CURRENT IN SINOATRIAL NODE CELLS OF THE RABBIT HEART [J].
HAGIWARA, N ;
IRISAWA, H ;
KASANUKI, H ;
HOSODA, S .
JOURNAL OF PHYSIOLOGY-LONDON, 1992, 448 :53-72
[8]   MODULATION BY INTRACELLULAR CA-2+ OF THE HYPERPOLARIZATION-ACTIVATED INWARD CURRENT IN RABBIT SINGLE SINO-ATRIAL NODE CELLS [J].
HAGIWARA, N ;
IRISAWA, H .
JOURNAL OF PHYSIOLOGY-LONDON, 1989, 409 :121-141
[9]   CONTRIBUTION OF 2 TYPES OF CALCIUM CURRENTS TO THE PACEMAKER POTENTIALS OF RABBIT SINO-ATRIAL NODE CELLS [J].
HAGIWARA, N ;
IRISAWA, H ;
KAMEYAMA, M .
JOURNAL OF PHYSIOLOGY-LONDON, 1988, 395 :233-253
[10]   IMPROVED PATCH-CLAMP TECHNIQUES FOR HIGH-RESOLUTION CURRENT RECORDING FROM CELLS AND CELL-FREE MEMBRANE PATCHES [J].
HAMILL, OP ;
MARTY, A ;
NEHER, E ;
SAKMANN, B ;
SIGWORTH, FJ .
PFLUGERS ARCHIV-EUROPEAN JOURNAL OF PHYSIOLOGY, 1981, 391 (02) :85-100