Presynaptic Neuromuscular Inhibition by Porphobilinogen and Porphobilin
- 1 February 1971
- journal article
- Published by Proceedings of the National Academy of Sciences in Proceedings of the National Academy of Sciences of the United States of America
- Vol. 68 (2), 383-386
- https://doi.org/10.1073/pnas.68.2.383
Abstract
The rat hemidiaphragm was studied in vitro as a test system to evaluate the effects of heme precursors and the uroporphyrins upon neuromuscular excitability. Porphobilinogen and porphobilin had no effect on the resting miniature end-plate potential frequency, but the K(+)-augmented frequency was significantly reduced. Porphobilin and porphobilinogen gave 50% of their maximal effect at concentrations of 0.008 and 0.6 mug/ml, respectively; the effect increased with concentration. Uroporphyrin I at 0.05-1.0 mug/ml caused a 25% decrease in frequency, but the effect did not increase with concentration. At similar concentrations, uroporphyrin III was without effect. The concentrations of porphobilin and porphobilinogen effective in inhibiting the K(+) stimulation, which are several orders of magnitude lower than the effective concentrations of simple amino acids, are those which might reasonably be expected in the sera of patients with acute intermittent porphyria.Keywords
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