Sugimoto K, Teeter J H
Monell Chemical Senses Center, University of Pennsylvania, Philadelphia 19104.
J Gen Physiol. 1990 Oct;96(4):809-34. doi: 10.1085/jgp.96.4.809.
Voltage-dependent membrane currents of cells dissociated from tongues of larval tiger salamanders (Ambystoma tigrinum) were studied using whole-cell and single-channel patch-clamp techniques. Nongustatory epithelial cells displayed only passive membrane properties. Cells dissociated from taste buds, presumed to be gustatory receptor cells, generated both inward and outward currents in response to depolarizing voltage steps from a holding potential of -60 or -80 mV. Almost all taste cells displayed a transient inward current that activated at -30 mV, reached a peak between 0 and +10 mV and rapidly inactivated. This inward current was blocked by tetrodotoxin (TTX) or by substitution of choline for Na+ in the bath solution, indicating that it was a Na+ current. Approximately 60% of the taste cells also displayed a sustained inward current which activated slowly at about -30 mV and reached a peak at 0 to +10 mV. The amplitude of the slow inward current was larger when Ca2+ was replaced by Ba2+ and it was blocked by bath applied CO2+, indicating it was a Ca2+ current. Delayed outward K+ currents were observed in all taste cells although in about 10% of the cells, they were small and activated only at voltages more depolarized than +10 mV. Normally, K+ currents activated at -40 mV and usually showed some inactivation during a 25-ms voltage step. The inactivating component of outward current was not observed at holding potentials more depolarized -40 mV. The outward currents were blocked by tetraethylammonium chloride (TEA) and BaCl2 in the bath or by substitution of Cs+ for K+ in the pipette solution. Both transient and noninactivating components of outward current were partially suppressed by CO2+, suggesting the presence of a Ca2(+)-activated K+ current component. Single-channel currents were recorded in cell-attached and outside-out patches of taste cell membranes. Two types of K+ channels were partially characterized, one having a mean unitary conductance of 21 pS, and the other, a conductance of 148 pS. These experiments demonstrate that tiger salamander taste cells have a variety of voltage- and ion-dependent currents including Na+ currents, Ca2+ currents and three types of K+ currents. One or more of these conductances may be modulated either directly by taste stimuli or indirectly by stimulus-regulated second messenger systems to give rise to stimulus-activated receptor potentials. Others may play a role in modulation of neurotransmitter release at synapses with taste nerve fibers.(ABSTRACT TRUNCATED AT 400 WORDS)
运用全细胞和单通道膜片钳技术，对从虎螈（钝口螈属）幼体舌头分离出的细胞的电压依赖性膜电流进行了研究。非味觉上皮细胞仅表现出被动膜特性。从味蕾分离出的细胞，推测为味觉感受器细胞，在从 -60 或 -80 mV 的钳制电位进行去极化电压阶跃时，会产生内向和外向电流。几乎所有的味觉细胞都表现出一种瞬时内向电流，该电流在 -30 mV 时激活，在 0 到 +10 mV 之间达到峰值并迅速失活。这种内向电流被河豚毒素（TTX）阻断，或者通过在浴液中用胆碱替代 Na⁺ 来阻断，这表明它是一种 Na⁺ 电流。大约 60% 的味觉细胞还表现出一种持续内向电流，该电流在约 -30 mV 时缓慢激活，在 0 到 +10 mV 时达到峰值。当 Ca²⁺ 被 Ba²⁺ 替代时，缓慢内向电流的幅度更大，并且它被浴液中添加的 Co²⁺ 阻断，这表明它是一种 Ca²⁺ 电流。在所有味觉细胞中都观察到了延迟外向 K⁺ 电流，尽管在大约 10% 的细胞中，它们很小，并且仅在比 +10 mV 更去极化的电压下激活。正常情况下，K⁺ 电流在 -40 mV 时激活，并且在 25 毫秒的电压阶跃期间通常会表现出一些失活。在钳制电位更去极化至 -40 mV 时，未观察到外向电流的失活成分。外向电流被浴液中的氯化四乙铵（TEA）和 BaCl₂ 阻断，或者通过在吸管溶液中用 Cs⁺ 替代 K⁺ 来阻断。外向电流的瞬时和非失活成分都被 Co²⁺ 部分抑制，这表明存在一种 Ca²⁺ 激活的 K⁺ 电流成分。在味觉细胞膜的细胞贴附式和外翻式膜片中记录到了单通道电流。部分鉴定了两种类型的 K⁺ 通道，一种平均单位电导为 21 pS，另一种电导为 148 pS。这些实验表明，虎螈味觉细胞具有多种电压和离子依赖性电流，包括 Na⁺ 电流、Ca²⁺ 电流和三种类型的 K⁺ 电流。这些电导中的一种或多种可能直接由味觉刺激调节，或者间接由刺激调节的第二信使系统调节，从而产生刺激激活的受体电位。其他的可能在与味觉神经纤维突触处神经递质释放的调节中起作用。（摘要截断于 400 字）
