Ewald D A, Roper S D
Department of Anatomy and Neurobiology, Colorado State University, Fort Collins 80523.
J Neurosci. 1994 Jun;14(6):3791-804. doi: 10.1523/JNEUROSCI.14-06-03791.1994.
Pairs of taste cells were impaled with intracellular recording microelectrodes in intact taste buds in slices of Necturus lingual epithelium. Applying short pulses of 140 mM KCl or 200 mM CaCl2 solutions to the apical pore elicited receptor potentials in taste receptor cells. Chemostimulation of receptor cells elicited postsynaptic responses in basal cells in the taste bud. Postsynaptic responses in basal cells had a threshold for activation and did not saturate with increasing doses of chemical stimulus applied to the receptor cells. We directly depolarized individual receptor cells and tested whether this would evoke postsynaptic responses in basal cells. Depolarizing receptor cells to approximately 0 mV evoked small depolarizing responses in basal cells in 16% of the experiments. The properties of these responses were consistent with their being mediated by a chemical synapse. A comparison of the responses in basal cells evoked by depolarizing single receptor cells, with responses evoked by stimulating the entire receptor cell population with KCl suggests that there is extensive synaptic convergence from receptor cells onto each basal cell. We also tested whether electrical excitation of basal cells would elicit (retrograde) synaptic responses in receptor cells. Single depolarizing pulses (up to 1 sec duration) applied to basal cells through the intracellular recording microelectrode never evoked synaptic responses in receptor cells. However, when repetitive electrical stimuli were applied to basal cells (four to six 1 sec depolarizations to approximately 0 mV every 12 sec) we observed prolonged effects on receptor cells in 11 of 23 experiments. These effects included an increase in the amplitude of receptor potentials elicited by KCI (mean +/- SD = +19 +/- 5%), an increase in membrane input resistance of receptor cells (+27 +/- 11%), and a hyperpolarization of receptor cells (3-10 mV). In control experiments, repetitive stimulation of one receptor cell never elicited such effects in another receptor cell. We investigated the possibility that serotonin (5-HT), released from basal cells, mediated the above modulatory effects on receptor cells. Bath-applied 5-HT (100 microM) mimicked the effects produced by repetitive basal cell stimulation (KCI responses increased by 23 +/- 12%; input resistance increased by 24 +/- 11%; hyperpolarization of 5-15 mV; N = 14). We conclude that basal cells release 5-HT onto adjacent taste receptor cells and that this enhances the electrotonic propagation of receptor potentials from the apical (chemosensitive) tip to the basal (synaptic) processes of receptor cells. The net effect is that activation of basal cells effectively increases the chemosensitivity of taste receptor cells.
用细胞内记录微电极刺入美西螈舌上皮切片中完整味蕾内的成对味觉细胞。向顶端小孔施加140 mM KCl或200 mM CaCl₂溶液的短脉冲，可在味觉受体细胞中引发受体电位。对受体细胞的化学刺激在味蕾的基底细胞中引发突触后反应。基底细胞中的突触后反应有激活阈值，并且不会随着施加到受体细胞上的化学刺激剂量增加而饱和。我们直接使单个受体细胞去极化，并测试这是否会在基底细胞中引发突触后反应。在16%的实验中，将受体细胞去极化至约0 mV会在基底细胞中引发小的去极化反应。这些反应的特性与它们由化学突触介导一致。将单个受体细胞去极化所引发的基底细胞反应，与用KCl刺激整个受体细胞群体所引发的反应进行比较，表明从受体细胞到每个基底细胞存在广泛的突触汇聚。我们还测试了对基底细胞的电刺激是否会在受体细胞中引发（逆行）突触反应。通过细胞内记录微电极向基底细胞施加单个去极化脉冲（持续时间长达1秒），从未在受体细胞中引发突触反应。然而，当对基底细胞施加重复性电刺激时（每12秒进行四到六次1秒的去极化至约0 mV），在23个实验中的11个实验中，我们观察到对受体细胞有延长的影响。这些影响包括KCl引发的受体电位幅度增加（平均值±标准差 = +19±5%）、受体细胞膜输入电阻增加（+27±11%）以及受体细胞超极化（3 - 10 mV）。在对照实验中，对一个受体细胞的重复性刺激从未在另一个受体细胞中引发此类影响。我们研究了基底细胞释放的5 - 羟色胺（5 - HT）介导上述对受体细胞调节作用的可能性。浴加5 - HT（100 microM）模拟了重复性基底细胞刺激产生的效果（KCl反应增加23±12%；输入电阻增加24±11%；超极化5 - ！5 mV；N = 14）。我们得出结论，基底细胞将5 - HT释放到相邻的味觉受体细胞上，这增强了受体电位从顶端（化学敏感）尖端到受体细胞基底（突触）部分的电紧张性传播。最终效果是基底细胞的激活有效地增加了味觉受体细胞的化学敏感性。
