Purkinje세포에서 Nitric Oxide에 의한 Na+-Ca2+전환 조절

초록

In the cerebellum, long-term depression (LTD) of synaptic transmission between parallel fibers (PFs) and Purkinje cells (PCs) involves the influx of Ca2+ into PCs through voltage-gated Ca2+ channels and the activation of a-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors and type-1 G-protein-coupled metabotropic receptors (mGluR1) and nitric oxide (NO)-dependent production of cGMP in PCs. In this study, we investigated the presence and physiological role of NCX and focused particularly on the interaction of NCX after AMPA receptor activation. The distribution of NCX and nNOS was investigated using 3,3'-diaminobenzidine (DAB) in cerebellar slices (4 weeks S.D. rat) and in situ hybridization technique. We also measured [Ca2+]i and NO concentration in cultured PCs, using Ca2+-sensitive fluorescent probe, Fura-2 and NO-sensitive fluorescent probe, 4,5-diaminofluorescein/diacetate (DAF-2/DA), respectively, with following results. 1. NCX1 is a predominant isoform expressed in the soma of PCs. 2. Removal of extracellular Na+ induced a transient rise of [Ca2+]i and reperfusion of extracellular Na+ lowered [Ca2+]i to the basal level via NCX. 3. Bepridil, a forward mode inhibitor, enhanced the expression of nNOS and fluorescence intensity of DAF-2/DA, but 7-nitroindazol, specific nNOS inhibitor, blocked these effects of bepridil. The expression of nNOS and fluorescence intensity of DAF-2DA were augmented by both the application of AMPA and bepridil. Our results imply that the activation of AMPA receptors enhances nNOS expression and NCX may modulate NO production in PCs.