Rise of intrasynaptosomal Ca2+ level and activation of nitric oxide synthase in adult rat cerebral cortex pretreated with 3-5-3'-L-triiodothyronine.

Accumulation of free, ionized calcium (Ca2+) and stimulation of nitric oxide synthase (NOS) activity in depolarization-induced synaptosomes prepared from adult rat cerebral cortex have been demonstrated after addition of various doses (0.1-1,000 nM) of 3,5,3'-L-triiodothyronine (T3). The effects of T3 doses on those parameters are found to occur in a dose-dependent manner. The T3 (100 nM)-induced optimum rise in intrasynaptosomal Ca2+ level [Ca2+]i seems to be an early event occurring within 5 s; whereas, the maximum stimulation of NOS activity is observed during 10 to 30 s of T3 (100 nM) administration, indicating a delayed effect. T3 has no such effects on those parameters in synaptosomes at nondepolarized condition. Although the rise in [Ca2+]i and stimulation of NOS activity after application of T3 seem to be sequential events, the present data indicate a definite role of T3 in nongenomic signal generation and transfer in mature rat cerebral cortex.