Williams P J, MacVicar B A, Pittman Q J
Neuroscience Research Group, University of Calgary, Alberta, Canada.
J Neurosci. 1990 Mar;10(3):748-56. doi: 10.1523/JNEUROSCI.10-03-00748.1990.
Intracellular recordings for current and voltage clamping were obtained from 130 neuroendocrine cells of the pars intermedia (PI) in intact pituitaries maintained in vitro. Spontaneous and evoked action potentials were blocked by TTX or by intracellular injection of a local anesthetic, QX-222. After potassium (K+) currents were blocked by tetraethylammonium (TEA), 4-aminopyridine, and intracellular cesium (Cs+), 2 distinct calcium (Ca2+) spikes were observed which were differentiated by characteristic thresholds, durations, and amplitudes. Both Ca2+ spikes were blocked by cobalt (Co2+) but were unaffected by TTX or QX-222. The low-threshold spike (LTS) had a smaller amplitude and inactivated when membrane potential was depolarized past -40 mV or when evoked at a fast rate (greater than 0.5 Hz). The high-threshold spike (HTS) typically had a larger amplitude and longer duration, was not inactivated at potentials which inactivated the LTS, and could be evoked at rates of up to 10 Hz. Single-electrode voltage-clamp analysis revealed that 3 distinct components of the Ca2+ current were present in most cells. From a negative holding potential (-90 mV), 2 separate peak inward currents were observed; a low-threshold transient current, similar to a T-type Ca2+ current, activated at -40 mV, whereas a large-amplitude inactivating current activated above -20 mV. This large inactivating Ca2+ current was significantly inactivated at a holding potential of -40 mV or by brief prepulses to positive potentials, and was similar to an N-type Ca2+ current. A sustained Ca2+ current (L-type) was observed which was not altered by different holding potentials.(ABSTRACT TRUNCATED AT 250 WORDS)
在体外培养的完整垂体中，从中间部（PI）的130个神经内分泌细胞进行了用于电流钳制和电压钳制的细胞内记录。自发和诱发动作电位被河豚毒素（TTX）或通过细胞内注射局部麻醉剂QX - 222阻断。在用四乙铵（TEA）、4 - 氨基吡啶和细胞内铯（Cs⁺）阻断钾（K⁺）电流后，观察到2种不同的钙（Ca²⁺）尖峰，它们通过特征阈值、持续时间和幅度来区分。两种Ca²⁺尖峰均被钴（Co²⁺）阻断，但不受TTX或QX - 222影响。低阈值尖峰（LTS）幅度较小，当膜电位去极化超过 - 40 mV或快速诱发（大于0.5 Hz）时失活。高阈值尖峰（HTS）通常幅度较大、持续时间较长，在使LTS失活的电位下不会失活，并且可以以高达10 Hz的频率诱发。单电极电压钳分析表明，大多数细胞中存在3种不同的Ca²⁺电流成分。从负的钳制电位（ - 90 mV）开始，观察到2个分开的内向电流峰值；一个低阈值瞬态电流，类似于T型Ca²⁺电流，在 - 40 mV时激活，而一个大幅度失活电流在 - 20 mV以上激活。这种大幅度失活的Ca²⁺电流在 - 40 mV的钳制电位下或通过短暂的正向预脉冲显著失活，并且类似于N型Ca²⁺电流。观察到一种持续的Ca²⁺电流（L型），其不受不同钳制电位的影响。（摘要截于250字）
