1. The protein complexin and its role in
coupling secretory vesicles and Ca2+
channels
Quintana J., Rohan J., Chow R.H.
Department of Physiology & Biophysics and Zilkha
Neurogenetic Institute,
Keck School of Medicine, University of Southern,
California, Los Angeles

2. Big Picture
• understand better how secretion is regulated
• use the acquired knowledge to create a
solution against diseases which there is not
enough secretion
• Example: type 2 diabetes

3. Background

4. Hormones Exocytosis
• signaling molecules
• stored in vesicle
• example: insulin
• process by which the
membrane of a vesicle
fuses with the cell
plasma membrane, and
the vesicle contents are
secreted
Vesicles
• to be readily
releasable, they
have to be docked
and primed

5. SNARE Complex
It assist exocytosis
through “zippering”
cartoon
more secretion when present
Complexin

6. Calcium & Ca2+ Channels
• triggers exocytosis
• vesicles nearer to Ca2+ channels secrete more reliably
• Readily Releasable Pool (RRP): primed vesicles both
near and far from Ca2+ channels
• Immediately Releasable Pool (IRP): primed vesicles
near Ca2+ channels
RRP & IRP

7. Question
Does the protein complexin help
vesicles to associate with calcium
channels?

8. Hypothesis
Cplx facilitates co-localization of
vesicles and Ca2+ channels.
We expect to see a change in the IRP if a
cell is missing Cplx (i.e. Cplx knock out)
IRP (WT) IRP (KO)
>
RRP RRP
Wild Type Knock Out
RRP IRP RRP IRP

9. Methods

10. Genotyping
• KO mice
– Adrenal chromaffin cells from litter mates of Cplx
+/-(hemizygous) mice
KO Bands
WT Bands
L 1 2 3 4 5 6 7 8 9 10 11
HZ WT KO

11. Patch Clamp
• biophysical tool
• Capacitance (C): electrical measurement that is
proportional to the area of the cell membrane
• IRP = ∑∆C short
• RRP = ∑∆C short + ∑∆C long
Modified from Sakmann and Neher, Sci. Am.
1991

12. short depolarization
protocol
long depolarization protocol
Depolarization

13. How to measure the IRP & RRP
∑∆C short
∑∆C long
~IRP
~RRP
Adapted from Voets et al., Neuron 23, 607 (1999).

14. Capacitance Data

15. Conclusion
• Our preliminary data supports our hypothesis
that Cplx helps co-localize vesicles and Ca2+
channels.
• Data needs to be replicated and statistically
validated.
• If validated, then Cplx serves not only to help
prime vesicles, but also to increase reliability
of stimulus-secretion coupling.

16. Acknowledgements
• Dr. Robert Chow
• Chow’s Lab
– Joyce G. Rohan
– Madison Zitting
– Alan Okada
• Dr. Emil Bogenmann
• NIH
– Step Up Program
ZNI

17. Question