Noradrenaline synthesis after sympathetic nerve activation in rat atria and its dependence on calcium but not CAM kinase II and protein kinases A or C
Abstract
1. The biosynthesis of noradrenaline following sympathetic nerve activation was investigated in rat atria. In particular the time course of noradrenaline synthesis changes, the relationship of changes in synthesis to transmitter release and the possible roles of second messengers and protein kinases were examined. 2. Rat atria incubated with the precursor [3H]-tyrosine synthesized [3H]-noradrenaline. Synthesis was enhanced following pulsatile electrical field stimulation (3 Hz for 5 min) with the bulk of the increase occurring in the first 45 min after the commencement of electrical stimulation. In separate experiments rat atria were pre-incubated with [3H]-noradrenaline and the radioactive outflow in response to electrical field stimulation (3 Hz for 5 min) was taken as an index of noradrenaline release. 3. Stimulation-induced (S-I) noradrenaline synthesis was significantly correlated to S-I noradrenaline release for a variety of procedures which modulate noradrenaline release by mechanisms altering Ca2+ entry into the neurone (r2 = 0.99): those which decreased release: tetrodotoxin (0.3 microM), Ca(2+)-free medium, lowering the frequency of nerve activation to 1 Hz, and those which increased release, tetraethylammonium (0.3 m...Continue Reading
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