Mechanisms of the neuromuscular blocking activity of the aminoglycoside antibiotic streptomycin.

While increasing the spontaneous quantal transmitter release in frog neuromuscular junctions, streptomycin blocked the evoked transmitter release by decreasing the quantal content (m). The quantal parameter of release n (number of release sites) was significantly decreased, while p (probability of release through transmitter activation) increased. Streptomycin competes with calcium ions for the membrane release sites while the intracellular mechanisms of release remain unaffected. The data show a good fit to the two-step hypothesis of quantal transmitter release recently developed on the basis of ouabain actions.