AJP - Cell Physiology, Vol 252, Issue 1 C55-C62, Copyright © 1987 by American Physiological Society
Cation dependence of posttetanic potentiation of neuromuscular transmission
S. Misler, L. Falke and S. Martin
We have investigated the possibility that much of posttetanic potentiation
(PTP) of quantal release of neurotransmitter at the frog neuromuscular
junction may be due to posttetanic accumulation of [Ca2+]i, via a
plasmalemmal Cao2+-Nai+ exchanger that is powered by an increase in Nai+
during the tetanus. Our new findings on the cationic dependence of PTP are
consistent with this hypothesis. 1) Several manuevers that decrease Na+-K+
pump activity, (decreasing [K+]o, replacing K+o with Rb+o or Li+o, or
adding acetylstrophanthidin to Ringers), all increase the intratetanic rise
and prolong the posttetanic decay of epp quantal content (m) and miniature
epp frequency (fmepp). 2) Increasing [Ca2+]i or [Sr2+]o, but not [Mg2+]o,
increases posttetanic fmepp in a graded fashion. 3) PTP of fmepp is still
present after addition of Mn2+o, which blocks voltage dependent Ca2+ entry.
