Alteration of the fast excitatory postsynaptic current by barium in voltage-clamped amphibian sympathetic ganglion cells.
Barium-induced alterations in fast excitatory postsynaptic currents (e.p.s.cs) have been studied in voltage-clamped bullfrog sympathetic ganglion B cells. In the presence of 2-8 mM barium, e.p.s.c. decay was prolonged and in many cells the e.p.s.c. decay phase deviated from a single exponential function. The decay phase in these cases was more accurately described as the sum of two exponential functions. The frequency of occurrence of a complex decay increased both with increasing barium concentration and with hyperpolarization. Miniature e.p.s.c. decay also was prolonged in barium-treated cells. E.p.s.c. amplitude was not markedly affected by barium (2-8 mM) in cells voltage-clamped to -50 mV whereas at -90 mV there was a progressive increase in peak size with increasing barium concentration. In control cells the e.p.s.c.-voltage relationship was linear between -20 and -100 mV; however, this relationship became progressively non-linear with membrane hyperpolarization in barium-treated cells. The e.p.s.c. reversal potential was shifted to a more negative value in the presence of barium. There was a voltage-dependent increase in charge movement during the e.p.s.c. in barium-treated cells which was not present in control cells. We conclude that the voltage-dependent alteration in e.p.s.c. decay time course, peak amplitude and charge movement in barium-treated cells is due to a direct postsynaptic action of barium on the kinetics of receptor-channel gating in postganglionic sympathetic neurones.
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D001464:Barium / Q000494:pharmacology*; D005728:Ganglia, Sympathetic / Q000187:drug effects*; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects; D011892:Rana catesbeiana; D011978:Receptors, Nicotinic / Q000187:drug effects
D011978:Receptors, Nicotinic; D001464:Barium