Nerve activity but not intracellular calcium determines the time course of endocytosis at the frog neuromuscular junction.
We used FM1-43 imaging and intracellular recordings of synaptic potentials to measure the time course of endocytosis in frog motor nerve terminals following tetanic nerve stimulation, and we used fura-2 imaging of intraterminal Ca2+ concentration to compare endocytic rate and [Ca2+]i. Following a 30 Hz tetanus, endocytosis declined exponentially with a time constant that depended on the duration of stimulation. The level of [Ca2+]i rose from a resting value of about 100 nM to more than 500 nM during 30 Hz stimulation, and rapidly declined to 200-250 nM after stimulation. [Ca2+]i returned to resting level with a time course that, like endocytosis, depended on the duration of tetanic stimulation. However, the rate of [Ca2+]i recovery was much slower than the rate of endocytosis, leading to the conclusion that endocytic rate is not determined solely by the instantaneous level of [Ca2+]i.
Department of Physiology, University of Colorado Medical School, Denver 80262, USA.
L G
LG
Wu
W J
WJ
Betz
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004558:Electric Stimulation; D004705:Endocytosis; D005456:Fluorescent Dyes; D016257:Fura-2; D066298:In Vitro Techniques; D007700:Kinetics; D008564:Membrane Potentials; D018482:Muscle, Skeletal / Q000294:innervation; D009469:Neuromuscular Junction / Q000502:physiology*; D011726:Pyridinium Compounds; D000644:Quaternary Ammonium Compounds; D011894:Rana pipiens; D013569:Synapses / Q000502:physiology*; D013997:Time Factors
C073804:FM1 43; D005456:Fluorescent Dyes; D011726:Pyridinium Compounds; D000644:Quaternary Ammonium Compounds; D002118:Calcium; D016257:Fura-2