Tsunenari T, Kaneko A
Department of Physiology, Keio University School of Medicine, Tokyo, Japan.
Ann N Y Acad Sci. 1998 Nov 30;855:148-9. doi: 10.1111/j.1749-6632.1998.tb10557.x.
It has been shown that quinine, a bitter tasting substance, induces a cationic membrane current in frog taste receptor cells. We analyzed the quinine-induced current fluctuation to further characterize the cationic channel conducting the current. Taste cells were enzymatically isolated from fungiform papillae of the bullfrog tongue. Membrane currents were recorded under voltage-clamp by using the whole-cell patch clamp technique. A Cs(+)-containing pipette solution was used to block K+ currents. When quinine was bath applied, it induced a steady inward current in cells held at -60 mV. The current data were digitized at a sampling frequency of 2 kHz after having been low-pass filtered (cut-off frequency, 1 kHz). The spectral density distribution was calculated by 1024 points fast Fourier transform (FFT), and was fitted by a sum of two Lorentzian functions, with corner frequencies at 10-20 Hz and at 90-120 Hz. The single-channel conductance calculated from the variance versus mean current plot was 5 pS in a normal saline solution containing 1.8 mM Ca2+. In a nominally Ca(2+)-free solution, the single-channel current was doubled. Our previous study has shown that the quinine-induced current is enhanced in low extracellular [Ca2+]. This enhancement could be partly attributable to the Ca2+ suppression of the single-channel conductance.
业已表明，奎宁这种苦味物质可在蛙类味觉受体细胞中诱导出阳离子膜电流。我们分析了奎宁诱导的电流波动，以进一步表征传导该电流的阳离子通道。从牛蛙舌头的菌状乳头中酶解分离出味觉细胞。使用全细胞膜片钳技术在电压钳制下记录膜电流。使用含铯（Cs⁺）的微电极内液来阻断钾离子电流。当将奎宁施加于浴槽时，它在保持于 -60 mV 的细胞中诱导出稳定的内向电流。电流数据在经过低通滤波（截止频率为 1 kHz）后以 2 kHz 的采样频率进行数字化。通过 1024 点快速傅里叶变换（FFT）计算频谱密度分布，并由两个洛伦兹函数之和拟合，其转折频率分别在 10 - 20 Hz 和 90 - 120 Hz。在含有 1.8 mM 钙离子的正常盐溶液中，根据方差与平均电流图计算出的单通道电导为 5 pS。在名义上无钙离子的溶液中，单通道电流翻倍。我们之前的研究表明，在低细胞外钙离子浓度下，奎宁诱导的电流会增强。这种增强可能部分归因于钙离子对单通道电导的抑制作用。
