Inhibition of spontaneous transmitter release by the membrane ligand cationized ferritin

Exposure of the frog neuromuscular junction to cationized ferritin (200 micrograms ml-1) results in a reduction in MEPP frequency of approximately 25% within 10 min. This effect is not dependent on extracellular Ca2+, and identical results are obtained in salines buffered with EGTA. It is suggested that cationized ferritin does not inhibit transmitter release via a reduction in the intracellular Ca2+ concentration, but exerts its effect by a direct action on exocytosis. A mode of action is proposed. Unlike Con A, cationized ferritin is unable to suppress the stimulation of spontaneous release caused by high osmolarity.