Bandeira-Duarte C, Carvalho C A, Cragoe Júnior E J, Carvalho A P
Department of Zoology, University of Coimbra, Portugal.
Neurochem Res. 1990 Mar;15(3):313-20. doi: 10.1007/BF00968678.
Preparations of synaptosomes isolated in sucrose or in Na(+)-rich media were compared with respect to internal pH (pHi), internal Ca2+ concentration ([Ca2+]i), membrane potential and 45Ca2+ uptake due to K+ depolarization and Na+/Ca2+ exchange. We found that synaptosomes isolated in sucrose media have a pHi of 6.77 +/- 0.04 and a [Ca2+]i of about 260 nM, whereas synaptosomes isolated in Na(+)-rich ionic media have a pHi of 6.96 +/- 0.07 and a [Ca2+]i of 463 nM, but both types of preparations have similar membrane potentials of about -50 mV when placed in choline media. The sucrose preparation takes up Ca2+ only by voltage sensitive calcium channels (VSCC'S) when K(+)-depolarized, while the Na(+)-rich synaptosomes take up 45Ca2+ both by VSCC'S and by Na+/Ca2+ exchange. The amiloride derivative 2',4'-dimethylbenzamil (DMB), at 30 microM, inhibits both mechanisms of Ca2+ influx, but 5-(N-4-chlorobenzyl)-2',4' dimethylbenzamil (CBZ-DMB), at 30 microM, inhibits the Ca2+ uptake by VSCC'S, but not by Na+/Ca2+ exchange. Thus, DMB and CBZ-DMB permit distinguishing between Ca2+ flux through channels and through Na+/Ca2+ exchange. We point out that the different properties of the two types of synaptosomes studied account for some of the discrepancies in results reported in the literature for studies of Ca2+ fluxes and neurotransmitter release by different types of preparations of synaptosomes.
对在蔗糖或富含Na⁺的培养基中分离得到的突触体进行了内部pH值（pHi）、内部Ca²⁺浓度（[Ca²⁺]i）、膜电位以及由K⁺去极化和Na⁺/Ca²⁺交换引起的⁴⁵Ca²⁺摄取方面的比较。我们发现，在蔗糖培养基中分离得到的突触体pHi为6.77±0.04，[Ca²⁺]i约为260 nM，而在富含Na⁺的离子培养基中分离得到的突触体pHi为6.96±0.07，[Ca²⁺]i为463 nM，但当置于胆碱培养基中时，两种类型的制剂具有相似的膜电位，约为 -50 mV。当K⁺去极化时，蔗糖制剂仅通过电压敏感钙通道（VSCC）摄取Ca²⁺，而富含Na⁺的突触体则通过VSCC和Na⁺/Ca²⁺交换摄取⁴⁵Ca²⁺。30 μM的氨氯地平衍生物2',4'-二甲基苯甲酰胺（DMB）抑制Ca²⁺内流的两种机制，但30 μM的5-(N-4-氯苄基)-2',4'-二甲基苯甲酰胺（CBZ-DMB）抑制VSCC对Ca²⁺的摄取，但不抑制Na⁺/Ca²⁺交换。因此，DMB和CBZ-DMB可以区分通过通道的Ca²⁺通量和通过Na⁺/Ca²⁺交换的Ca²⁺通量。我们指出，所研究的两种类型突触体的不同特性解释了文献中关于不同类型突触体制剂的Ca²⁺通量和神经递质释放研究结果的一些差异。
