Dual effect of potassium on transmitter exocytosis

F. Grohovaz, R. Fesce, C. Haimann

Research output: Contribution to journalArticlepeer-review


The time course of exocytosis of quanta of acetylcholine induced by 20 mM K+ was studied at the frog neuromuscular junction. Images of vesicle fusion on freeze-fracture replicas were mostly localized at the active zones in resting preparations fixed in 20 mM K+. Fusions appreared also outside the active zones in preparations fixed after 1 min exposure to 20 mM K + and were evenly distributed over the presynaptic membrane after 5 min in 20 mM K+ (even though secretion was prevented by withdrawing Ca2+ until 30 s before fixation). The mean densities of vesicle fusions were comparable in all conditions, as were the total number of quanta released during the fixation period. This indicates that fusions outside active zones represent ectopic exocytosis, slowly activated by potassium. Partial inactivation of K+-induced quantal release (time and concentration-dependent) was observed electrophysiologically; this may be related to the observed decrease in density of vesicle fusions along the active zones, with time. Consistently, after 5 min in 15 mM K + fusion density at the active zones remained high. It is concluded that active zone-associated and ectopic fusions are two exocytotic processes activated with differential time courses and concentration-dependence by K +.

Original languageEnglish
Pages (from-to)1085-1095
Number of pages11
JournalCell Biology International Reports
Issue number12
Publication statusPublished - 1989

ASJC Scopus subject areas

  • Cell Biology


Dive into the research topics of 'Dual effect of potassium on transmitter exocytosis'. Together they form a unique fingerprint.

Cite this