Devor D C, Simasko S M, Duffey M E
Department of Physiology, School of Medicine, State University of New York, Buffalo 14214.
Am J Physiol. 1990 Feb;258(2 Pt 1):C318-26. doi: 10.1152/ajpcell.1990.258.2.C318.
Effects of carbachol on membrane potential and current in T84 cells were determined using whole cell patch-clamp techniques. When the pipettes contained a standard KCl solution and the bath contained a standard NaCl solution, carbachol (100 microM) caused a rapid hyperpolarization to the K+ equilibrium potential (EK+), followed by potential oscillations. When membrane potential was clamped to 0 mV, carbachol induced an outwardly directed K+ current in 31 of 37 cells, with a peak value of 618 +/- 51 (SE) pA. In 77% of these cells the current oscillated and gradually declined to base line. Atropine (20 microM) blocked this response. In symmetric KCl solutions the carbachol-induced current reversed at 0 mV with no rectification. Ba2+ or Cs+ did not block the current, but tetraethylammonium ion (TEA) reduced the number of responding cells. Although a Cl- conductance was found in resting cells, carbachol did not cause an increase in Cl- current when the cells were voltage-clamped to EK+, or when voltage-clamped to +/- 60 mV while bathed in symmetric NaCl solutions. When the Ca2(+)-buffering capacity of the pipette solution was increased, 80% of the cells responded to carbachol, but only 10% oscillated; however, no K+ current was induced by carbachol when the pipette was made nominally Ca2+ free. The current was not affected by removal of Ca2+ from the bath. These results show that carbachol induces an oscillating Ca2(+)-activated K+ conductance in T84 cells, but no Cl- conductance. This K+ conductance is dependent on the mechanisms that regulate intracellular Ca2+.
使用全细胞膜片钳技术测定了卡巴胆碱对T84细胞的膜电位和电流的影响。当移液管中含有标准KCl溶液且浴槽中含有标准NaCl溶液时，卡巴胆碱（100微摩尔）引起快速超极化至K⁺平衡电位（EK⁺），随后出现电位振荡。当膜电位钳制在0 mV时，卡巴胆碱在37个细胞中的31个细胞中诱导出外向的K⁺电流，峰值为618±51（SE）皮安。在这些细胞的77%中，电流振荡并逐渐下降至基线。阿托品（20微摩尔）阻断了这种反应。在对称的KCl溶液中，卡巴胆碱诱导的电流在0 mV时反转，无整流现象。Ba²⁺或Cs⁺不阻断电流，但四乙铵离子（TEA）减少了反应细胞的数量。尽管在静息细胞中发现了Cl⁻电导，但当细胞电压钳制在EK⁺时，或在对称NaCl溶液中电压钳制在±60 mV时，卡巴胆碱并未引起Cl⁻电流增加。当移液管溶液的Ca²⁺缓冲能力增加时，80%的细胞对卡巴胆碱有反应，但只有10%振荡；然而，当移液管中名义上不含Ca²⁺时，卡巴胆碱未诱导出K⁺电流。电流不受浴槽中Ca²⁺去除的影响。这些结果表明，卡巴胆碱在T84细胞中诱导出振荡性的Ca²⁺激活的K⁺电导，但无Cl⁻电导。这种K⁺电导依赖于调节细胞内Ca²⁺的机制。
