Alvarez L J, Candia O A, Zamudio A C
Department of Ophthalmology, Mount Sinai School of Medicine, New York, NY 10029, USA.
Exp Eye Res. 1995 Aug;61(2):129-40. doi: 10.1016/s0014-4835(05)80032-6.
Rabbit lenses were bathed within a bicameral Ussing-type chamber under short-circuit conditions. In this situation the short-circuit current (Isc) reflects, across the anterior aspect, the presence of anteriorly facing K+ conductance(s) plus the Na(+)-K+ pump current. Across the posterior surface the Isc is primarily carried by the movement of Na+ from the posterior bathing solution to the lens. Addition of acetylcholine (ACh) to the posterior hemichamber did not affect the translens electrical parameters; but, its introduction to the anterior bath at 1 microM immediately reduced the Isc from 8.91 +/- 1.47 to 5.84 +/- 1.28 microA cm-2 and increased the translens resistance from 1.50 +/- 0.08 to 1.59 +/- 0.09 K omega cm2 (+/- S.E.S; P < 0.05 as paired values, n = 25 lenses). The suppressed Isc gradually recovered and reached 75% of the control value 5 min after the introduction of the neurotransmitter. In six cases the recovery was nearly complete (> or = 95% of control) within this time. The preaddition of 0.1 microM atropine prevented an effect by 1 microM ACh. When atropine was added within 1 min of ACh, the suppressed Isc immediately recovered. The ACh-elicited Isc suppression was averted in lenses pre-exposed to either K+ channel blockers (quinidine or barium) or to the endoplasmic reticular Ca(2+)-ATPase inhibitor thapsigargin (Tg: 0.1 microM), which in itself produced Isc inhibitions similar to those seen with ACh under control conditions. Similarly comparable were the ACh-evoked Isc inhibitions garnered upon introduction of the agonist to lenses bathed in the absence of extracellular Ca2+. In these cases, however, the Isc recovered fully within 2-3 min. This condition also revealed that the anterior removal of medium Ca2+ increased the Isc by about 50%, a completely reversible phenomenon; Ca2+ restoration in the presence of the Ca2+ channel blocker, nifedipine (10 microM), blunted markedly the reversal to the control Isc. Overall, these results suggest that ACh receptor activation induces the release of intracellularly stored Ca2+, which in turn leads to the temporary deactivation of a K+ conductance(s); in addition, secondary Ca2+ inflow may further extend the observed inhibition. During this study, the Isc of about 30% of the lenses used spontaneously oscillated (common duration of 30 min, with a mean peak frequency of 0.76 +/- 0.32 cycle min-1 and mean amplitude of 4.07 +/- 2.65 microA cm-2; +/- S.D.S, n = 24). Experiments attempted to determine the sensitivity of the oscillatory activity to ACh. Tg, nifedipine, and the phorbol ester PMA.(ABSTRACT TRUNCATED AT 400 WORDS)
兔晶状体在短路条件下置于双室Ussing型小室中。在这种情况下，短路电流（Isc）在前表面反映了面向前的K⁺电导的存在以及Na⁺ - K⁺泵电流。在后表面，Isc主要由Na⁺从后浴液向晶状体的移动所携带。向后半室添加乙酰胆碱（ACh）不影响跨晶状体电参数；但是，在1微摩尔浓度下将其加入前浴立即将Isc从8.91±1.47微安/平方厘米降低至5.84±1.28微安/平方厘米，并使跨晶状体电阻从1.50±0.08千欧厘米²增加至1.59±0.09千欧厘米²（±标准误；配对值P < 0.05，n = 25个晶状体）。被抑制的Isc逐渐恢复，在引入神经递质5分钟后达到对照值的75%。在6个案例中，在此时间内恢复几乎完全（≥对照值的95%）。预先添加0.1微摩尔阿托品可防止1微摩尔ACh的作用。当在ACh加入后1分钟内添加阿托品时，被抑制的Isc立即恢复。在预先暴露于K⁺通道阻滞剂（奎尼丁或钡）或内质网Ca²⁺ - ATP酶抑制剂毒胡萝卜素（Tg：0.1微摩尔）的晶状体中，ACh引起的Isc抑制被避免，毒胡萝卜素本身在对照条件下产生与ACh类似的Isc抑制。同样可比的是，将激动剂引入无细胞外Ca²⁺的浴中的晶状体时获得的ACh诱发的Isc抑制。然而，在这些情况下，Isc在2 - 3分钟内完全恢复。这种情况还表明，前介质中Ca²⁺的去除使Isc增加约50%，这是一个完全可逆的现象；在Ca²⁺通道阻滞剂硝苯地平（10微摩尔）存在下恢复Ca²⁺可显著减弱向对照Isc的逆转。总体而言，这些结果表明ACh受体激活诱导细胞内储存的Ca²⁺释放，这反过来又导致K⁺电导的暂时失活；此外，继发性Ca²⁺内流可能进一步延长观察到的抑制作用。在这项研究中，约30%的所用晶状体的Isc自发振荡（常见持续时间为30分钟，平均峰值频率为0.76±0.32次/分钟，平均振幅为4.07±2.65微安/平方厘米；±标准差，n = 24）。实验试图确定振荡活动对ACh的敏感性。Tg、硝苯地平和佛波酯PMA。（摘要截断于400字）
