Sitges M, Reyes A, Chiu L M
División de Investigaciones Clínicas, Instituto Mexicano de Psiquiatría, SSA, Mexico.
J Neurosci Res. 1994 Sep 1;39(1):11-22. doi: 10.1002/jnr.490390103.
Using a rapid (0.5 ml/min) flow rate superfusion system, the dopamine (DA) transporter mediated release of DA is further explored, and compared to the depolarization evoked release of DA in rat striatal synaptosomes preloaded with radioactive DA (3H-DA). In this system external DA in the low microM range efficaciously releases the preloaded transmitter, the maximal response being reached at 3 microM DA. The external DA stimulated release is Ca(2+)-independent, Cl(-)-dependent, and blocked by both bupropion and nomifensine. The atypical antidepressant bupropion inhibits 3H-DA accumulation to rat striatal synaptosomes with a calculated IC50 of 1.3 x 10(-6) M. Among DA uptake blockers some are known to act as DA releasing agents. Here we found that the DA uptake blocker nomifensine (30 microM) is unable to modify the baseline release of 3H-DA, whereas bupropion (10 microM) clearly elevates the baseline release of 3H-DA in a Ca(2+)-independent and Cl(-)-dependent manner. The non releasing agent nomifensine blocks the release of 3H-DA induced by bupropion. The Ca(2+)-dependent, high K+ depolarization evoked release of 3H-DA is not modified by nomifensine and does not depend on the external Cl- concentration. When the depolarizing medium contains DA the carrier mediated release of 3H-DA induced by the external DA is additive to the high K+ induced response. A drastic drop in the external Cl- concentration induces 3H-DA release. This release of 3H-DA induced by low external Cl- levels is completely blocked by nomifensine, which only slightly diminished the release of 3H-DA induced by the absence of external Na+. On the basis of these results, it is concluded that: 1) Rapid perfusion flow rates eliminate DA reuptake. 2) DA uptake inhibitors either with or without DA releasing capabilities block the release of DA induced by microM levels of external DA. 3) By preventing translocation of the DA transporter mobile moiety, nomifensine may inhibit the release of DA induced by external DA or bupropion and by drastic drops in the external Cl- concentration. 4) In the absence of nomifensine, the DA transporter works under both resting and depolarized conditions, but in contrast to the GABA transporter (Sitges et al.: Neurochem Res 18:1081-1087, 1993), the DA transporter does not contribute to the amount of the DA released by depolarization. 5) Reversal of the DA uptake carrier is favored by conditions increasing the internal DA levels. 6) Cl- rather than Na+ is a major determinant in 3H-DA movements through the DA transporter.
使用快速（0.5毫升/分钟）流速的灌注系统，进一步探究多巴胺（DA）转运体介导的DA释放，并与预先加载放射性DA（3H-DA）的大鼠纹状体突触体中去极化诱发的DA释放进行比较。在该系统中，低 microM 范围内的外部DA有效地释放预先加载的递质，在3 microM DA时达到最大反应。外部DA刺激的释放不依赖Ca(2+)，依赖Cl(-)，并被安非他酮和诺米芬辛阻断。非典型抗抑郁药安非他酮抑制3H-DA在大鼠纹状体突触体中的积累，计算出的IC50为1.3×10(-6)M。在DA摄取阻滞剂中，有些已知可作为DA释放剂。在此我们发现，DA摄取阻滞剂诺米芬辛（30 microM）无法改变3H-DA的基线释放，而安非他酮（10 microM）则以不依赖Ca(2+)和依赖Cl(-)的方式明显提高3H-DA的基线释放。非释放剂诺米芬辛阻断安非他酮诱导的3H-DA释放。诺米芬辛不改变Ca(2+)依赖的、高K+去极化诱发的3H-DA释放，且该释放不依赖外部Cl-浓度。当去极化介质中含有DA时，外部DA诱导的3H-DA载体介导的释放与高K+诱导的反应相加。外部Cl-浓度的急剧下降诱导3H-DA释放。低外部Cl-水平诱导的这种3H-DA释放被诺米芬辛完全阻断，而诺米芬辛仅轻微减少外部Na+缺失诱导的3H-DA释放。基于这些结果，得出以下结论：1）快速灌注流速消除DA再摄取。2）具有或不具有DA释放能力的DA摄取抑制剂阻断 microM 水平的外部DA诱导的DA释放。3）通过阻止DA转运体可移动部分的易位，诺米芬辛可能抑制外部DA或安非他酮以及外部Cl-浓度急剧下降诱导的DA释放。4）在没有诺米芬辛的情况下，DA转运体在静息和去极化条件下均起作用，但与GABA转运体（Sitges等人：《神经化学研究》18:1081 - 1087，1993）不同，DA转运体对去极化释放的DA量没有贡献。5）内部DA水平升高的条件有利于DA摄取载体的逆转。6）Cl-而非Na+是3H-DA通过DA转运体移动的主要决定因素。
