Electrogenesis of the slow inhibitory postsynaptic potential in bullfrog sympathetic ganglia.
The ionic mechanisms of the slow surface positive (P)-potential and the slow inhibitory postsynaptic potential (IPSP), an intracellularly recorded P-potential in sympathetic ganglia, were analysed by means of sucrose-gap, intracellular microelectrode techniques, and voltage clamp technique. Both the P-potential and the slow IPSP consist of two different potential components, namely the ouabain-sensitive and the ouabain-insensitive components. The ouabain-sensitive component was enhanced by a moderate conditioning hyperpolarization. This component was most reasonably explained as a potential change generated by an activation of the electrogenic Na+ pump. The ouabain-insensitive potential component of the P-potential and the slow IPSP decreased in the amplitude and finally reversed its polarity by conditioning hyperpolarization. The reversal potential of ouabain-insensitive component of slow IPSP and slow inhibitory postsynaptic current (IPSC) was close to the EK. The amplitude of ouabain-insensitive component of P-potential and slow IPSP was markedly decreased by an elevation of external K+ concentration. The reversal potential of ouabain-insensitive component shifted to a more positive potential level in high K+ Ringer's solution. On the other hand, it was augmented in K+-free Ringer's solution. A reduction of the membrane resistance was observed during the generation of the slow IPSP, when the membrane potential of ganglion cells was held at a membrane potential level more negative than -60 mV. The slow IPSC recorded by voltage-clamp method was associated with an increase in membrane conductance. It was concluded that the ouabain-insensitive component was generated by an activation of K+ conductance.
D000818:Animals; D005728:Ganglia, Sympathetic / Q000502:physiology*; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects; D009433:Neural Inhibition; D009538:Nicotine / Q000494:pharmacology; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D011892:Rana catesbeiana; D012964:Sodium / Q000378:metabolism
D010042:Ouabain; D009538:Nicotine; D012964:Sodium; D011188:Potassium