Tetanic potentiation of miniature end-plate potential frequency at frog neuromuscular junction in manganese solutions
Narita, K.
Nihon Seirigaku Zasshi. Journal of the Physiological Society of Japan 47(12): 746-755
1985
ISSN/ISBN: 0031-9341 PMID: 3007749 Document Number: 256754
Using a sciatic nerve-sartorius muscle preparation of the frog, we have studied the effect of Mn on the increase in miniature end-plate potential (MEPP) frequency that occurs during tetanic stimulation (50 Hz, 2-3 min) of the nerve in nominally Ca2+-free, Mn2+ and Mg2+ solutions. During stimulation the frequency increased over the first minutes to reach an asymptote. The time course for the increase was analyzed following the model proposed by Barton, Cohen and Van der Kloot (1983). The ratio of the Ca2+ bound to the receptor at intervals during the tetanus, b, to the Ca2+ bound before stimulation was begun, b0, was calculated from MEPP frequencies. b/b0 indicates changes in intraterminal Ca2+ concentration produced by the tetanus. In solutions made with no added Ca2+ but containing 1 mM MgEGTA, the increase in b/b0 during stimulation showed a linear or convex time course. Similar time courses were obtained in solutions containing Mn2+ or Mg2+ as the sole divalent cation. On the other hand, when solutions contained Ca2+, the time course for the increase followed a sigmoidal curve. The present results suggest that Mn2+ enters the nerve terminal during stimulation and raises the intracellular Ca2+ concentration, which in turn promotes transmitter release.