title: Cation dependence of posttetanic potentiation of neuromuscular transmission.
abstract: 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.
mesh_terms: D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002412:Cations; D066298:In Vitro Techniques; D007700:Kinetics; D008094:Lithium / Q000494:pharmacology; D008274:Magnesium / Q000494:pharmacology; D009119:Muscle Contraction / Q000187:drug effects; D009469:Neuromuscular Junction / Q000187:drug effects / Q000502:physiology*; D011188:Potassium / Q000494:pharmacology*; D011894:Rana pipiens; D012413:Rubidium / Q000494:pharmacology; D013324:Strontium / Q000494:pharmacology
chemical_list: D002412:Cations; D008094:Lithium; D008274:Magnesium; D012413:Rubidium; D011188:Potassium; D002118:Calcium; D013324:Strontium