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This Article Full Text Full Text (PDF) All Versions of this Article: 101/2/1103    most recent 90483.2008v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Maeda, M. Articles by Akaike, N. Search for Related Content PubMed PubMed Citation Articles by Maeda, M. Articles by Akaike, N.

Differential Effects of Divalent Cations on Spontaneous and Evoked Glycine Release From Spinal Interneurons

¹Department of Physiology, Kurume University School of Medicine, Kurume; ²Graduate School of Science and Technology, Kumamoto University, Kumamoto; and ³Research Division for Life Sciences, Kumamoto Health Science University, Kumamoto, Japan

Submitted 18 April 2008; accepted in final form 30 September 2008

The effects of Ca²⁺, Sr²⁺, and Ba²⁺ on spontaneous and evoked glycinergic inhibitory postsynaptic currents (mIPSCs and eIPSCs) were studied using the "synaptic bouton" preparation of rat spinal neurons and conventional whole cell recording under voltage-clamp conditions. In response to application of Ca²⁺-free solution, the frequency of mIPSC initially rapidly decreased to 4050% of control followed by a gradual further decline in mIPSC frequency to 30% of control. Once mIPSC frequency had significantly decreased in Ca²⁺-free solution, application of Ca²⁺, Sr²⁺, or Ba²⁺ increased mIPSC frequency. The rank order of effect in restoring mIPSCs was Ba²⁺ >> Ca²⁺ > Sr²⁺. Moreover, the application of excess external [K⁺]_o solution (30 mM) containing Sr²⁺ or Ba²⁺ after 2 h in Ca²⁺-free solution also increased mIPSC frequency in the order Sr²⁺ Ba²⁺ > Ca²⁺. The mean mIPSC amplitude was not affected at all. In contrast, eIPSCs produced by focal stimulation of single boutons were completely abolished in Ca²⁺-free solution or when Ca²⁺ was replaced by Sr²⁺ or Ba²⁺ (2 mM each). However, eIPSCs were restored in increased concentrations of Sr²⁺ or Ba²⁺ (5 mM each). The results show that these divalent cations affect mIPSC and eIPSCs differently and indicate that the mechanisms underlying transmitter release that generates eIPSCs and mIPSC in presynaptic nerve terminals are different. The different mechanisms might be explained by the different sensitivity of synaptotagmin isoforms to Ca²⁺, Sr²⁺, and Ba²⁺.