Properties of inwardly rectifying K+ channels in ventricular myocytes

Summary The voltage- and time-dependent properties of whole-cell, multi-channel (outside-out), and single channel inwardly-rectifying K⁺ currents were studied using adult and neonatal rat, and embryonic chick ventricular myocytes. Inward rectification of the current-voltage relationship was found in the whole-cell and single channel measurements. The steady-state single channel probability of opening decreased with hyperpolarization from E_K, as did the mean open time, thereby explaining the time-dependent inactivation of the macroscopic current. Myocytes dialysed with a Mg⁺⁺-free K⁺ solution (to remove the property of inward rectification) displayed a quasi-linear current-voltage relationship. The outward K⁺ currents flowing through the modified inward rectifier channels were able to be blocked by the local anesthetic and anti-arrhythmic agent, lidocaine.     

Inwardly rectifying whole-cell and single-channel K currents in the murine macrophage cell line J774.1

Summary Inward currents in the murine macrophage-like cell line J774.1 were studied using the whole-cell and cell-attached variations of the patch-clamp technique. When cells were bathed in Na Hanks' (KCl=4.5mm, NaCl=145mm), and the electrode contained Na-free K Hanks' (KCl=145mm) single-channel currents were observed at potentials below –40 mV which showed inward rectification, were K-selective, and were blocked by 2.5mm Ba in the pipette. Single-channel conductance was 29 pS, and was proportional to the square root of [K] _o . Channels manifested complex kinetics, with multiple open and closed states. The steady-state open probability of the channel was voltage dependent, and declined from 0.9 to 0.45 between –40 and –140 mV. When hyperpolarizing voltage pulses were repetitively applied in the cell-attached patch mode, averaged single-channel currents showed inactivation. Inactivation of inwardly rectifying whole-cell current was measured in Na Hanks' and in two types of Na-free Hanks': one with a normal K concentration (4.5mm) and the other containing 145mm K. Inactivation was shown to have Na-dependent and Na-independent components. Properties of single-channel current were found to be sufficient to account for the behavior of the macroscopic current, except that single-channel current showed a greater degree of Na-independent inactivation than whole-cell current.     

Inwardly rectifying potassium current in rabbit osteoclasts: A whole-cell and single-channel study

Summary Ionic conductances of rabbit osteoclasts were investigated using both whole-cell and cell-attached configurations of the patch-clamp recording technique. The predominant conductance found in these cells was an inwardly rectifying K⁺ conductance. Whole-cell currents showed an N-shaped current-voltage (I–13;V) relation with inward current activated at potentials negative to E_K. When external K⁺ was varied, I-V curves shifted 53 mV/10-fold change in [K⁺]_out, as predicted for a K⁺-selective channel. Inward current was blocked by Ba²⁺ and showed a time-dependent decline at negative potentials, which was reduced in Na⁺-free external solution. Inward single-channel currents were recorded in the cell-attached configuration. Single-channel currents were identified as inward-rectifier K⁺ channels based on the following observations: (i) Unitary I-V relations rectified, with only inward current resolved. (ii) Unitary conductance () was 31 pS when recorded in the cell-attached configuration with 140 mm K⁺ in the pipette and was found to be dependent on [K⁺]. (iii) Addition of Ba²⁺ to the pipette solution abolished single-channel events. We conclude that rabbit osteoclasts possess inwardly rectifying K⁺ channels which give rise to the inward current recorded at negative potentials in the whole-cell configuration. This inwardly rectifying K⁺ current may be responsible for setting the resting membrane potential and for dissipating electrical potential differences which arise from electrogenic transport of protons across the osteoclast ruffled border.This work was supported by The Arthritis Society and the Medical Research Council of Canada. M.E.M.K. was supported by a fellowship, S.J.D. a development Grant and S.M.S. a scholarship from the Medical Research Council. We thank Dr. Zu Gang Zheng for help with scanning microscopy.     

Quantitative analysis of outward rectifying K+ channel currents in guard cell protoplasts fromVicia faba

Summary A quantitative analysis of the time and voltage dependence of outward-rectifying K⁺ currents ( ) in guard cells fromVicia faba is described using the whole-cell patch-clamp technique. After step depolarizations from –75 mV to potentials positive to –40 mV, time-dependent outward currents were produced, which have recently been identified as K⁺ channel currents. This K⁺ current was characterized according to its time dependence and its steady-state activation. could be described in terms of a Hodgkin-Huxley type conductance. Activation of the current in time was sigmoid and was well fitted by raising the activation variable to the second power. Deactivating tail currents were single exponentials, which suggests that only one conductance underlies this slow outward K⁺ current. Rates of channel closing were strongly dependent on the membrane potential, while rates of channel opening showed only limited voltage dependence leading to a highly asymmetric voltage dependence for channel closing and opening. The presented analysis provides a quantitative basis for the understanding of channel gating and channel functions in plant cells.     

Barium- and calcium-permeable channels open at negative membrane potentials in rat ventricular myocytes

Summary Ca²⁺- and Ba²⁺-permeable channel activity from adult rat ventricular myocytes, spontaneously appeared in the three single-channel recording configurations: cell-attached, and excised inside-out or outside-out membrane patches. Single-channel activity was recorded at steady-state applied membrane potentials including the entire range of physiologic values, and displayed no rundown in excised patches. This activity occurred in irregular bursts separated by quiescent periods of 5 to 20 min in cell-attached membrane patches, whereas in excised patch experiments, this period was reduced to 2 to 10 min. During activity, a variety of kinetic behaviors could be observed with more or less complex gating patterns. Three conductance levels: 22, 45 and 78 pS were routinely observed in the same excised membrane patch, sometimes combining to give a larger level. These channels were significantly permeable to divalent cations and showed little or no permeability to potassium or sodium ions. The inorganic blockers of voltage-gated Ca channels, cobalt (2mm), cadmium (0.5mm) or nickel (3mm), had no apparent effect on these spontaneous unitary currents carried by barium ions. Under 10^–5 m bay K 8644 or nitrendipine, the activity was clearly increased in about half of the tested excised inside-out membrane patches. Both dihydropyridines enhanced openings of the larger conductance level, which was only very occasionally seen under control conditions. When the single-channel activity became sustained under 5×10^–6 m Bay K 8644, it was possible to calculate the mean unitary current at different membrane potentials and show that the mean current value increased with membrane potential.     

Permeance of Cs+ and Rb+ through the inwardly rectifying K+ channel in guinea pig ventricular myocytes

Summary Inward currents carried by external Cs, Rb, NH₄ and K through theI _K1 channel were studied using a whole-cell voltage clamp technique. Cs, NH₄, and Rb currents could be recorded negative to –40 mV following depolarizing prepulses (0 mV and 200–1000 msec in duration). The current activation displayed an instantaneous component followed by a monoexponential increase () to a peak amplitude. Subsequent inactivation was fit by a single exponential, _i. With hyperpolarization, and _i decreasede-fold per 36 and 25 mV, respectively. In Ca-free external solutions (pipette [Mg]0.3mm), inactivation was absent, consistent with the hypothesis that inactivation represents time- and voltage-dependent block of Cs, NH₄, and Rb currents by external Ca. The inactivation and degree of steady-state block was greatest when Cs was the charge carrier, followed by NH₄, and then Rb. K currents, however, did not inactivate in the presence of Ca. Na and Li did not carry any significant current within the resolution of our recordings. Comparison ofpeak inward current ratios (I _x/I_K) as an index of permeability revealed a higher permeance of Cs (0.15), NH₄ (0.30), and Rb (0.51) relative to K (1.0) than that obtained by comparing thesteady-state current ratios (CsNH₄RbK0.010.060.211.0). At any given potential, was smaller the more permeant the cation. In the absence of depolarizing prepulses, the amplitude of was reduced. Divalent-free solutions did not significantly affect activatio in the presence of 0.3mm pipette [Mg]. When pipette [Mg] was buffered to 50 m, however, removal of external Ca and Mg lead to a four- to fivefold increase in Cs currents and loss of both time-dependent activation and inactivation (reversible upon repletion of external Ca).These results suggest that (i) permeability ratios forI _K1 should account for differences in the degree to which monovalent currents are blocked by extracellular Ca and (ii) extracellular or intracellular divalent cations contribute to the slow phase of activation which may represent either (a) the actual rate of Mg or Ca extrusion from the channel into the cell, a process which may be enhanced by repulsive interaction with the incoming permeant monovalent cation or (b) an intrinsic gating process that is strongly modulated by the permeant monovalent ion and divalent cations.     

Tamoxifen inhibits Na+ and K+ currents in rat ventricular myocytes

Tamoxifen is an estrogen receptor antagonist used in the treatment of breast cancer. However, tamoxifen has been shown to induce QT prolongation of the electrocardiogram, thereby potentially causing life-threatening polymorphic ventricular arrhythmias. The purpose of the present study was to elucidate the electrophysiological mechanism(s) that underlie the arrhythmogenic effects of tamoxifen. We used standard ruptured whole cell and perforated patch-clamping techniques on rat ventricular myocytes to investigate the effects of tamoxifen on cardiac action potential (AP) waveforms and the underlying K+ currents. Tamoxifen (3 micromol/l) markedly prolonged AP duration, decreased maximal rate of depolarization, and decreased resting membrane potential. At this concentration, tamoxifen significantly depressed the Ca2+-independent transient outward K+ current (Ito), sustained outward delayed rectifier K+ current (Isus), inward rectifier K+ current (IK1), and Na+ current (INa) in the myocytes. Lower concentrations of tamoxifen (1 micromol/l) also decreased the resting membrane potential and significantly depressed IK1 to 79 +/- 5% (n = 5; at -120 mV) of pretreatment values. The results of this study indicate that inhibition of Ito, Isus, and IK1 by tamoxifen may underlie AP prolongation in cardiac myocytes and thereby contribute to prolonged QT interval observed in patients.     

蛋白激酶A和蛋白激酶C对豚鼠心肌细胞延迟整流钾电流的作用

目的 :研究蛋白激酶A和蛋白激酶C对豚鼠心室肌细胞延迟整流钾电流 (Ik)的影响。方法 :采用电极内液浓度差扩散法进行细胞内给药 ,利用全细胞膜片箝技术测定单细胞Ik。结果 :cAMP15 0 μmol/L使Ik及Ik ,tail(pA/pF)从 13.7± 2 .1和 6 .1± 0 .3增至 18.5± 3.3和 6 .4± 2 .1(P <0 .0 1,n =6 ) ;8 CPT cAMP15 0 μmol/L使电流 (pA/pF)从 11.4± 1.8及 5 .3± 0 .6增至 17.9± 4 .0和 6 .2± 1.3,PKA的选择性抑制剂 6 2 2 1.0 μmol/L的可逆转二者的作用。cAMP使Ik的激活曲线左移 ,半激活电压 (V1/ 2 )从 2 3.3mV移至 18.7mV ,激活曲线斜率 (k)在用药前后变化较小。 10 μmol/LPMA可以分别使Ik和Ik ,tial(pA/pF)从 12 .9± 1.8和 5 .0± 1.7升至 2 3.7± 2 .8和 7.5±1.1。PMA使I V曲线幅值增加 ,并随去极化电压的升高其作用加强 ,同时PMA使通道的激活曲线k从 15 .3mV升到 2 5 .6mV ,但对V1/ 2 基本无影响。结论 :蛋白激酶A和蛋白激酶C均可增加豚鼠心肌细胞Ik,但二者作用特点有所不同     

Four kinetically distinct depolarization-activated K+ currents in adult mouse ventricular myocytes

In the experiments here, the time- and voltage-dependent properties of the Ca2+-independent, depolarization-activated K+ currents in adult mouse ventricular myocytes were characterized in detail. In the majority (65 of 72, approximately 90%) of cells dispersed from the ventricles, analysis of the decay phases of the outward currents revealed three distinct K+ current components: a rapidly inactivating, transient outward K+ current, Ito,f (mean +/- SEM taudecay = 85 +/- 2 ms); a slowly (mean +/- SEM taudecay = 1,162 +/- 29 ms) inactivating K+ current, IK,slow; and a non inactivating, steady state current, Iss. In a small subset (7 of 72, approximately 10%) of cells, Ito,f was absent and a slowly inactivating (mean +/- SEM taudecay = 196 +/- 7 ms) transient outward current, referred to as Ito,s, was identified; the densities and properties of IK,slow and Iss in Ito,s-expressing cells are indistinguishable from the corresponding currents in cells with Ito,f. Microdissection techniques were used to remove tissue pieces from the left ventricular apex and from the ventricular septum to allow the hypothesis that there are regional differences in Ito,f and Ito,s expression to be tested directly. Electrophysiological recordings revealed that all cells isolated from the apex express Ito,f (n = 35); Ito,s is not detected in these cells (n = 35). In the septum, by contrast, all of the cells express Ito,s (n = 28) and in the majority (22 of 28, 80%) of cells, Ito,f is also present. The density of Ito,f (mean +/- SEM at +40 mV = 6.8 +/- 0.5 pA/pF, n = 22) in septum cells, however, is significantly (P < 0.001) lower than Ito,f density in cells from the apex (mean +/- SEM at +40 mV = 34.6 +/- 2.6 pA/pF, n = 35). In addition to differences in inactivation kinetics, Ito,f, Ito,s, and IK,slow display distinct rates of recovery (from inactivation), as well as differential sensitivities to 4-aminopyridine (4-AP), tetraethylammonium (TEA), and Heteropoda toxin-3. IK,slow, for example, is blocked selectively by low (10-50 microM) concentrations of 4-AP and by (>/=25 mM) TEA. Although both Ito,f and Ito,s are blocked by high (>100 microM) 4-AP concentrations and are relatively insensitive to TEA, Ito,f is selectively blocked by nanomolar concentrations of Heteropoda toxin-3, and Ito,s (as well as IK,slow and Iss) is unaffected. Iss is partially blocked by high concentrations of 4-AP or TEA. The functional implications of the distinct properties and expression patterns of Ito,f and Ito,s, as well as the likely molecular correlates of these (and the IK,slow and Iss) currents, are discussed.     

吗啡对新生鼠尾核神经元钾离子通道电流的作用

目的 :研究吗啡对新生鼠尾核神经元钾离子通道电流的作用。方法 :应用全细胞膜片钳技术在培养的尾核神经元上 ,观察吗啡急性与慢性处理对尾核神经元电压门控钾离子通道电流的影响。结果 :吗啡急性处理尾核神经元诱发钾离子通道电流增大 ,电流从加吗啡前的 (2 .6± 0 .4 )nA增高到 (3.3± 0 .5 )nA ,加纳洛酮后电流下降为 (2 .4± 0 .4 )nA ;吗啡慢性处理尾核神经元的钾离子通道电流从对照组的 (2 .6± 0 .4 )nA增高到 (3.1± 0 .5 )nA ,加纳洛酮后电流下降为 (2 .4± 0 .4 )nA。结论 :在吗啡急性或慢性处理尾核神经元后 ,吗啡经 μ受体介导 ,诱发尾核神经元钾离子通道电流增大 ,使神经元处于超极化状态 ,导致神经元活动的抑制     

Aging-associated changes in whole cell K(+) and L-type Ca(2+) currents in rat ventricular myocytes

The effect of aging on cardiac membrane currents remains unclear. This study examined the inward rectifier K(+) current (I(K1)), the transient outward K(+) current (I(to)), and the L-type Ca(2+) channel current (I(Ca,L)) in ventricular myocytes isolated from young adult (6 mo) and aged (>27 mo) Fischer 344 rats using whole cell patch-clamp techniques. Along with an increase in the cell size and membrane capacitance, aged myocytes had the same magnitude of peak I(K1) with a greater slope conductance but displayed smaller steady-state I(K1). Aged myocytes also had a greater I(to) with an increased rate of activation, but the I(to) inactivation kinetics, steady-state inactivation, and responsiveness to L-phenylephrine, an alpha(1)-adrenergic agonist, were unaltered. The magnitude of peak I(Ca,L) in aged myocytes was decreased and accompanied by a slower inactivation, but the I(Ca,L) steady-state inactivation was unaltered. Action potential duration in aged myocytes was prolonged only at 90% of full repolarization (APD(90)) when compared with the action potential duration of young adult myocytes. Aged myocytes from Long-Evans rats showed similar changes in I(to) and I(Ca,L) but an increased I(K1). These results demonstrate aging-associated changes in action potential, in morphology, and in I(K1), I(to), and I(Ca,L) of rat ventricular myocytes that possibly contribute to the decreased cardiac function of aged hearts.     

细胞外Ba2+对大鼠心肌细胞L型钙通道的影响

目的：观察细胞外Ba²⁺对记录大鼠心肌细胞L型钙通道的影响。方法：采用急性酶解分离法获得大鼠的单个心肌细胞,使用全细胞膜片钳技术记录L型钙通道电流。采用Ba²⁺替换台式液中的Ca²⁺和直接向台式液中加入Ba²⁺（0~8 mmol/L）,观察峰值电流15 min内的变化,数据采用5个以上细胞进行重复。结果：（1）台式液中的Ca²⁺被Ba²⁺替换后,L型钙通道电流的失活速率明显减慢（P<0.01）;在台式液中加入少量Ba²⁺（0.2,0.4 mmol/L）时L型钙通道电流的失活速率无明显改变（P>0.05）,加入0.8 mmol/L Ba²⁺时失活速率明显减慢（P<0.05）。（2）与正常台式液比较,在细胞外液中加入Ba²⁺（0.2,0.4 mmol/L）峰值电流衰减减弱,其中10 min和15 min两个时间点衰减差异明显（P<0.01）。（3）在细胞外液中加入Ba²⁺可下移电流电压曲线,改变翻转电位,减弱丹酚酸A对钙电流的抑制强度,使量效关系曲线右移。结论：在细胞外液中加入一定浓度的Ba²⁺,能够减弱全细胞膜片钳技术记录大鼠心室肌细胞L型钙通道时出现的峰值电流衰减,改变通道的电压依赖特性,影响药物量效关系。     

Gating and conductance in an outward-rectifying K+ channel from the plasma membrane of Saccharomyces cerevisiae

Summary The plasma membrane of the yeast Saccharomyces cerevisiae has been investigated by patch-clamp techniques, focusing upon the most conspicuous ion channel in that membrane, a K⁺-selective channel. In simple observations on inside-out patches, the channel is predominantly closed at negative membrane voltages, but opens upon polarization towards positive voltages, typically displaying long flickery openings of several hundred milliseconds, separated by long gaps (G). Elevating cytoplasmic calcium shortens the gaps but also introduces brief blocks (B, closures of 2–3 msec duration). On the assumption that the flickery open intervals constitute bursts of very brief openings and closings, below the time resolution of the recording system, analysis via the beta distribution revealed typical closed durations (interrupts, I) near 0.3 msec, and similar open durations. Overall behavior of the channel is most simply described by a kinetic model with a single open state (O), and three parallel closed states with significantly different lifetimes: long (G), short (B) and very short (I). Detailed kinetic analysis of the three open/closed transitions, particularly with varied membrane voltage and cytoplasmic calcium concentration, yielded the following stability constants for channel closure: K _I =3.3 · e ^–zu in which u=eV _m /kT is the reduced membrane voltage, and z is the charge number; K _G = 1.9 · 10^–4([Ca²⁺] · e ^zu )^–1; and K _B =2.7 · 10³([Ca²⁺] · e ^zu )². Because of the antagonistic effects of both membrane voltage (V _m ) and cytoplasmic calcium concentration ([Ca²⁺]_cyt) on channel opening from the B state, compared with openings from the G state, plots of net open probability (P ₀ ) vs. either V _m or [Ca²⁺] are bell-shaped, approaching unity at low calcium ( m) and high voltage (+150 mV), and approaching 0.25 at high calcium (10 mm) and zero voltage. Current-voltage curves of the open channel are sigmoid vs. membrane voltage, saturating at large positive or large negative voltages; but time-averaged currents, along the rising limb of P ₀ (in the range 0 to +150 mV, for 10 m [Ca²⁺]) make this channel a strong outward rectifier. The overall properties of the channel suggest that it functions in balancing charge movements during secondary active transport in Saccharomyces.The authors are indebted to Dr. Michael Snyder and Dr. Constance Copeland (Yale Department of Biology) for providing the tetraploid yeast strain and for initial assistance in handling the cells and preparing protoplasts; and to Dr. Esther Bashi for technical assistance throughout the experiments. The work was supported by Research Grant 85ER13359 from the United States Department of Energy (to C.L.S.), by Forschungs-Stipendium Be 1181/2-1 from the Deutsche Forschungsgemeinschaft (to A.B.), and by Akademie-Stipendium II/66647 from the Volkswagenstiftung (to D.G.).     

CoCl2预处理对大鼠海马神经元急性低氧后Na+、K+电流的影响

目的：观察氯化钴(COCl2)预处理对急性低氧后海马神经元电压门控性Na^ 、K^ 电流的影响。方法：原代培养大鼠海马神经元,分为COCl2预处理和非处理组,采用膜片钳全细胞记录技术,检测急性低氧后海马神经元钠电流(INa)、钾电流(Ik)的变化。结果：急性低氧后,海马神经元INa、Ik电流幅度明显降低,INa阈值右移,而经CoCl2预处理的海马神经元INa、Ik电流的降低幅度明显减轻。结论：COCl2预处理减轻急性低氧所致的INa、Ik电流变化,对神经元有明显的保护作用。     

Effect of Na i on activity and voltage dependence of the Na/K pump in adult rat cardiac myocytes

We have measured the voltage dependence of the Na/K pump in isolated adult rat cardiac myocytes using the whole-cell patch-clamp technique. In the presence of 1–2 mM Ba and 0.1 mm Cd and nominally Ca-free, Na/K pump current (I _p) was measured as the change in current due to 1 mM ouabain. Voltage dependence of I _pwas measured between –140 and +40 or +60 mV using square voltage-pulse and voltage-ramp protocols, respectively. With 150 mM extracellular Na (Na _o ) and 5.4 mM extracellular K (K _o ), we found that the Na/K pump shows a strong positive voltage dependence between –140 and 0 mV and is voltage independent at positive potentials. Removing Na _o reduced the voltage dependence at negative potentials with no effect at positive potentials. When K _o was reduced, a negative slope appeared in the current-voltage (I-V) curve at positive potentials. We have investigated whether Na _i (intracellular Na) might also affect the voltage dependence of I _pby varying Na in the patch pipette (Na_pip) between 20 and 85 mM. We found, as expected, that I _pincreased markedly as Na_pip was raised, saturating at about 70 mM Na_pip under these conditions. In contast, while I _psaturated near +20 mV and declined to about 40% of maximum at –120 mV, there was no effect of Na_pip under these conditions. In contrast, while I _psaturated near +20 mV and declined to about 40% of maximum at –120 mV, there was no effect of Na_pip on the voltage dependence of I _p. This suggests that neither Na _i binding to the Na/K pump nor the conformational changes dependent on Na _i binding are voltage dependent. These results are consistent with extracellular ion binding within the field of the membrane but do not rule out the possibility that other steps, such as Na translocation, are also voltage dependent.We wish to thank Ms. Melinda Price, Ms. Meei Liu and Mr. Randall Anderson for their technical assistance. This work was supported in part by National Institutes of Health grant HL44660.     

SO2代谢衍生物对大鼠海马CA1区神经元瞬间外向钾电流和延迟整流钾电流的影响

本文利用全细胞膜片钳技术研究了SO2 代谢衍生物———NaHSO3 和Na2 SO3 (二者分子比为 1∶3)对大鼠海马CA1区神经元瞬间外向钾电流 (IA)和延迟整流钾电流 (IK)的影响。结果表明 ,SO2 代谢衍生物可显著增大IA 和IK,且呈剂量依赖性关系 ,使IA 和IK 增大 5 0 %的剂量分别为 2 6 19μmol/L和 14 5 0 μmol/L。此外还与电压呈依赖性关系 ,但不具有频率依赖性。结果还表明 ,10 μmol/LSO2 代谢衍生物不影响IA 的激活过程 ,而对IK 的激活过程有非常显著的影响 ,给药前后IK 的半数激活电压分别为 17 6 4± 7 31mV和 13 43± 2 0 0mV (n=10 ,P <0 0 1) ,但不改变其斜率因子。另外 ,10 μmol/LSO2 代谢衍生物还非常显著地影响IA 的失活过程 ,给药前后其半数失活电压分别为 - 6 5 93± 1 97mV和 - 5 9 2 2± 3 83mV (n =10 ,P <0 0 1) ,但不改变其斜率因子。由此推断 ,SO2 代谢衍生物增大大鼠海马CA1区神经元的IA 和IK,促进IK 的激活过程 ,并抑制IA 的失活过程 ,可导致胞内K 通过K 通道的外流增加 ,胞内K 浓度降低 ,造成中枢神经元功能紊乱 ,诱导神经细胞凋亡。这意味着SO2 代谢衍生物对中枢神经系统具有损伤作用 ,从而提示大气SO2 污染可能与一些中枢神经系统疾病的发生以及衰老有关 [动物学报 49(1) :73     

Single-channel analysis of a potassium inward rectifier in myocytes of newborn rat heart

Summary Unitary K⁺ currents in single cells isolated from ventricular muscle of newborn rat hearts were measured in response to different potentials and [K] _o . TheI/V curves were linear for potentials more negative than the zero-current voltage: especially in high [K] _o (150nm KCl), no clear outward currents could be detected indicating a drastic rectification in the inward direction. The channel is mainly selective to K⁺ but Na⁺ ions are also carried (P _Na/P _K=0.056). The channel conductance is proportional to the square root of [K] _o but Na⁺ ions seem to have a facilitatory effect on _K, the single-channel conductance. The channel activity, measured asP _o, i.e. the probability to find the channel in open state, decreased as the membrane was hyperpolarized. This behavior was tentatively explained by an inactivation process as the membrane becomes more negative. The rate constants of the transitions between the different states were calculated according to a C–O–C model. A control of the gating process by permeant ion K⁺ was postulated, based on the increase of one of the rate constants from the closed to the open state with [K] _o . Finally, the macroscopicI/V curves calculated fromP _o and i, the unit current, were found to be characteristic of a ion-blocked inward rectifier.     

肾上腺髓质素对豚鼠心室肌细胞L-型钙通道的调制

应用全细胞膜片钳技术研究了肾上腺髓质素 (ADM )对豚鼠心室肌细胞L 型钙电流 (ICa ,L)的影响及其信号传导机制。结果发现 :ADM ( 1～ 10 0nmol/L)浓度依赖性抑制ICa,L(P <0 0 5 ) ,并可被ADM特异受体阻断剂ADM2 2 52 ( 10 0nmol/L)完全阻断。用蛋白激酶A特异拮抗剂H 89( 10 μmol/L)预处理 ,对ADM抑制ICa ,L的作用无影响。但用蛋白激酶C (PKC)特异性拮抗剂PKC19 36 预处理 ,可完全阻断ADM的抑制效应 ;而PKC特异性激动剂PMA则可以模仿ADM的抑制效应 (P <0 0 5 )。上述结果提示 :ADM作用于特异性ADM受体可浓度依赖性地抑制豚鼠心室肌细胞ICa ,L,而此作用可能是PKC介导的。