[Relation between the effect of carbacholine on spontaneous mediator release from motor nerve endings and extracellular potassium concentration in the rat].

The action of carbachol (10 microM/l) on miniature end-plate potentials (MEPP) frequency was studied in soleus muscle of rats during changes of extracellular potassium concentration from 2 to 15 mM. The cholinomimetic did not influence the spontaneous transmitter release within potassium concentration range from 2 to 7.5 mM and increased MEPP frequency with concentrations exceeding the 7.5 mM rate. This facilitating effect grew with potassium concentration and at 15 mM the MEPP frequency increased up to 160%. The data obtained supported the hypothesis according to which action of cholinomimetics on the spontaneous transmitter release realized by means of presynaptic cholinereceptors depends on the initial level of the membrane potential of nerve terminals.