Artalejo A R, García A G, Neher E
Departamento de Farmacología, Facultad de Medicina, Universidad Autónoma de Madrid, Spain.
Pflugers Arch. 1993 Apr;423(1-2):97-103. doi: 10.1007/BF00374966.
Simultaneous whole-cell patch-clamp and fura-2 fluorescence [Ca2+]i measurements were used to characterize Ca(2+)-activated K+ currents in cultured bovine chromaffin cells. Extracellular application of histamine (10 microM) induced a rise of [Ca2+]i concomitantly with an outward current at holding potentials positive to -80 mV. The activation of the current reflected an increase in conductance, which did not depend on membrane potential in the range -80 mV to -40 mV. Increasing the extracellular K+ concentration to 20 mM at the holding potential of -78 mV was associated with inwardly directed currents during the [Ca2+]i elevations induced either by histamine (10 microM) or short voltage-clamp depolarizations. The current reversal potential was close to the K+ equilibrium potential, being a function of external K+ concentration. Current fluctuation analysis suggested a unit conductance of 3-5 pS for the channel that underlies this K+ current. The current could be blocked by apamin (1 microM). Whole-cell current-clamp recordings showed that histamine (10 microM) application caused a transient hyperpolarization, which evolved in parallel with the [Ca2+]i changes. It is proposed that a small-conductance Ca(2+)-activated K+ channel is present in the membrane of bovine chromaffin cells and may be involved in regulating catecholamine secretion by the adrenal glands of various species.
采用全细胞膜片钳与fura-2荧光法同步测量培养的牛嗜铬细胞内的[Ca2+]i，以表征Ca(2+)激活的K+电流。细胞外施加组胺（10 microM）可使[Ca2+]i升高，同时在-80 mV以上的钳制电位下产生外向电流。电流的激活反映了电导的增加，在-80 mV至-40 mV范围内，电导不依赖于膜电位。在-78 mV的钳制电位下，将细胞外K+浓度增加到20 mM，在组胺（10 microM）或短时间电压钳去极化诱导的[Ca2+]i升高期间，会伴随内向电流。电流反转电位接近K+平衡电位，是外部K+浓度的函数。电流波动分析表明，构成该K+电流的通道的单位电导为3 - 5 pS。该电流可被蜂毒明肽（1 microM）阻断。全细胞电流钳记录显示，施加组胺（10 microM）会引起短暂的超极化，其变化与[Ca2+]i的变化平行。研究表明，牛嗜铬细胞膜上存在小电导Ca(2+)激活的K+通道，可能参与调节各种物种肾上腺的儿茶酚胺分泌。
