Biphasic behavior of fast endocitosis kinetics in mice chromaffin cells.

JOSÉ MOYA DÍAZ; FERNANDO D. MARENGO; LUCAS BAYONÉS

Buenos Aires

Congreso; 2nd FALAN Congress; 2016

Federation of Latinoamerican and Caribean Neuroscience Societies

Action potential like stimulus (APls) induces synchronous exocytosis (EXO) of few vesicles, followed by a fast, dynamin dependent, endocytosis (ENDO). In this work we studied the effect of the magnitude of stimulus on this endocytosis. First, we studied the effect of the duration of depolarization on the relation ENDO/EXO, which denotes the efficiency of endocytosis, and on the kinetics of ENDO. We found that ENDO was completely compensatory for APls (5 ms), since ENDO/EXO was 1.14±0.2. However, this parameter decreased with the length of depolarization, reaching a value of 0.37±0.09 for a 50ms squared depolarization. On the other hand, the time constant of ENDO (τ) showed an interesting biphasic behavior, increasing from 0.83±0.15s for APls to approximately 1.3s for 10 and 25ms squared depolarizations, and decreasing to 0.78±0.11s for a 50 ms squared depolarization. In a second protocol, we compared the effects of application of single, paired or triple 25ms squared depolarizations, applied at 20 Hz. The results were consistent with the previous: while ENDO/EXO decreases from single to paired stimulation, and remained stable afterwards; the τ of ENDO decreased with the number of depolarizing stimuli (τ25ms: 1.34±0.49s; τ 2x25ms: 0.53±0.15s; τ3x25ms: 0.35±0.05s). These results suggest that the magnitude of the stimulus regulates fast endocytosis in a biphasic fashion, provoking deceleration and acceleration of the process as the stimulus is prolonged respect to an APls.