Zhainazarov A B, Ache B W
Whitney Laboratory, University of Florida, 9505 Ocean Shore Blvd., St. Augustine, FL 32086, USA.
J Membr Biol. 1997 Mar 15;156(2):173-90. doi: 10.1007/s002329900199.
The gating and conduction properties of a channel activated by intracellular Na+ were studied by recording unitary currents in inside-out patches excised from lobster olfactory receptor neurons. Channel openings to a single conductance level of 104 pS occurred in bursts. The open probability of the channel increased with increasing concentrations of Na+. At 210 mm Na+, membrane depolarization increased the open probability e-fold per 36.6 mV. The distribution of channel open times could be fit by a single exponential with a time constant of 4.09 msec at -60 mV and 90 mm Na+. The open time constant was not affected by the concentration of Na+, but was increased by membrane depolarization. At 180 mm Na+ and -60 mV, the distribution of channel closed times could be fit by the sum of four exponentials with time constants of 0.20, 1.46, 8.92 and 69.9 msec, respectively. The three longer time constants decreased, while the shortest time constant did not vary with the concentration of Na+. Membrane depolarization decreased all four closed time constants. Burst duration was unaffected by the concentration of Na+, but was increased by membrane depolarization. Permeability for monovalent cations relative to that of Na+ (PX/PNa), calculated from the reversal potential, was: Li+ (1.11) > Na+ (1.0) > K+ (0.54) > Rb+ (0.36) > Cs+ (0.20). Extracellular divalent cations (10 mm) blocked the inward Na+ current at -60 mV according to the following sequence: Mn2+ > Ca2+ > Sr2+ > Mg2+ > Ba2+. Relative permeabilities for divalent cations (PY/PNa) were Ca2+ (39.0) > Mg2+ (34.1) > Mn2+ (15.5) > Ba2+ (13.8) > Na+ (1.0). Both the reversal potential and the conductance determined in divalent cation-free mixtures of Na+ and Cs+ or Li+ were monotonic functions of the mole fraction, suggesting that the channel is a single-ion pore that behaves as a multi-ion pore when the current is carried exclusively by divalent cations. The properties of the channel are consistent with the channel playing a role in odor activation of these primary receptor neurons.
通过记录从龙虾嗅觉受体神经元分离出的内面向外膜片上的单通道电流，研究了由细胞内Na⁺激活的通道的门控和传导特性。通道开放至单一电导水平104 pS呈簇状出现。通道的开放概率随Na⁺浓度增加而升高。在210 mM Na⁺时，膜去极化使开放概率每36.6 mV增加一倍。在-60 mV和90 mM Na⁺时，通道开放时间的分布可用单一指数拟合，时间常数为4.09毫秒。开放时间常数不受Na⁺浓度影响，但随膜去极化而增加。在180 mM Na⁺和-60 mV时，通道关闭时间的分布可用四个指数之和拟合，时间常数分别为0.20、1.46、8.92和69.9毫秒。三个较长的时间常数减小，而最短的时间常数不随Na⁺浓度变化。膜去极化使所有四个关闭时间常数减小。簇持续时间不受Na⁺浓度影响，但随膜去极化而增加。根据反转电位计算的单价阳离子相对于Na⁺的通透性（PX/PNa）为：Li⁺（1.11）> Na⁺（1.0）> K⁺（0.54）> Rb⁺（0.36）> Cs⁺（0.20）。细胞外二价阳离子（10 mM）在-60 mV时按照以下顺序阻断内向Na⁺电流：Mn²⁺> Ca²⁺> Sr²⁺> Mg²⁺> Ba²⁺。二价阳离子的相对通透性（PY/PNa）为：Ca²⁺（39.0）> Mg²⁺（34.1）> Mn²⁺（15.5）> Ba²⁺（13.8）> Na⁺（1.0）。在无二价阳离子的Na⁺与Cs⁺或Li⁺混合物中测定的反转电位和电导均为摩尔分数的单调函数，表明该通道是单离子孔，当电流仅由二价阳离子携带时表现为多离子孔。该通道的特性与它在这些初级受体神经元的气味激活中发挥作用一致。
