Winkler B S
Exp Eye Res. 1983 Apr;36(4):581-94. doi: 10.1016/0014-4835(83)90052-0.
The relative inhibitory effects of ATP depletion, ouabain and calcium on the receptor potential of the isolated rat retina were investigated. The principal experimental test used to assess these effects was the rate and extent of recovery of the receptor potential after re-establishing the transmembrane sodium gradient. Retinas were incubated in 25 mM-sodium for 10-20 min and then the external concentration of sodium was increased to 155 mM in control retinas, in retinas exposed to 10(-4) M-ouabain, and in retinas depleted of ATP (glucose-free medium plus 10 mM 2-deoxyglucose). Measurements showed that by 10-20 min ouabain completely inhibited the activity of the sodium-potassium ATPase and 2-deoxyglucose caused almost total loss of retinal ATP. In control retinas, the increase in sodium led to a rapid, full recovery of the receptor potential. When the sodium-potassium pump was blocked by ouabain, a return to the normal level of sodium led within seconds to a small (30%) recovery of the potential which decayed over 5 min. In ATP depleted retinas no recovery of the receptor potential was observed. However, if glucose was added at the time of changing to 155 mM-sodium in depleted retinas then a substantial recovery of the receptor potential was observed, but the return of the potential was delayed relative to the instantaneous re-establishment of the sodium gradient. After ouabain caused the receptor potential to decay in the presence of 2 mM-calcium and 155 mM-sodium, the potential was restored within seconds upon a reduction of external calcium to 10(-7)M. At this low calcium concentration, but not at 2 mM-calcium, an inverted receptor potential was observed transiently when the membrane sodium gradient was reversed during ouabain treatment. No recovery of the receptor potential was seen if the concentrations of calcium and sodium were raised to their control levels after incubation of the retina in a low sodium, low calcium, ouabain-containing medium. These results show that the receptor potential is elicited by changing the sodium gradient when the sodium-potassium pump is blocked, but is not evoked when either retinal ATP content is low or the external level of calcium is increased. The similarity in the inhibitory effects of ATP depletion and calcium suggest that high energy phosphates play a role in maintaining a low intracellular concentration of calcium, possibly by influencing sodium-calcium exchange or calcium pumps.
研究了ATP耗竭、哇巴因和钙对离体大鼠视网膜感受器电位的相对抑制作用。用于评估这些作用的主要实验测试是在重新建立跨膜钠梯度后感受器电位的恢复速率和程度。将视网膜在25 mM钠中孵育10 - 20分钟，然后在对照视网膜、暴露于10(-4)M哇巴因的视网膜以及ATP耗竭的视网膜（无葡萄糖培养基加10 mM 2-脱氧葡萄糖）中，将细胞外钠浓度增加到155 mM。测量结果表明，在10 - 20分钟时，哇巴因完全抑制了钠钾ATP酶的活性，2-脱氧葡萄糖导致视网膜ATP几乎完全丧失。在对照视网膜中，钠的增加导致感受器电位迅速、完全恢复。当钠钾泵被哇巴因阻断时，钠恢复到正常水平在几秒钟内导致电位小幅（30%）恢复，该恢复在5分钟内衰减。在ATP耗竭的视网膜中未观察到感受器电位的恢复。然而，如果在耗竭的视网膜中将钠浓度变为155 mM时添加葡萄糖，则观察到感受器电位有显著恢复，但相对于钠梯度的瞬间重建，电位的恢复延迟。在哇巴因使感受器电位在2 mM钙和155 mM钠存在下衰减后，当细胞外钙降至10(-7)M时，电位在几秒钟内恢复。在这个低钙浓度下，但不是在2 mM钙时，在哇巴因处理期间当膜钠梯度反转时短暂观察到倒置的感受器电位。如果在低钠、低钙、含哇巴因的培养基中孵育视网膜后将钙和钠的浓度提高到对照水平，则未观察到感受器电位的恢复。这些结果表明，当钠钾泵被阻断时，感受器电位是由改变钠梯度引发的，但当视网膜ATP含量低或细胞外钙水平升高时则不会诱发。ATP耗竭和钙的抑制作用的相似性表明，高能磷酸盐可能通过影响钠钙交换或钙泵在维持细胞内低钙浓度中起作用。
