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Secretion without membrane fusion: porocytosis
Robert B Silver1, George D Pappas
1Department of Pharmacology, School of Medicine, Wayne State University, Detroit, MI 48201, USA. rsilver@mbl.edu
Anatomical Record. Part B, New Anatomist
|January 27, 2005
Summary
We propose porocytosis, a new cell secretion mechanism. This model explains vesicular and constitutive secretion via transient calcium-mediated pores, fitting all physiological data.
Area of Science:
- Cell Biology
- Biophysics
Background:
- The current model of exocytotic secretion, involving vesicle and plasma membrane fusion, does not fully align with all physiological data.
- The energetics of lipid bilayers do not favor spontaneous fusion events.
Purpose of the Study:
- To propose a novel mechanism for cellular secretion, termed porocytosis.
- To provide a unifying framework for understanding both vesicular and constitutive secretion.
Main Methods:
- Investigated the physical and physicochemical interactions of calcium ions and phospholipids.
- Modeled the formation of transient pores between cellular membranes.
Main Results:
- Calcium ions (10^-4 to 10^-3 M) transiently form salt bridges between adjacent lipid molecules.
- This creates transient pores (approx. 1 nm diameter) spanning vesicle and plasma membranes.
- Pore lifetime is dependent on calcium ion levels, driving secretion via mass action.
Conclusions:
- The porocytosis hypothesis offers a physically plausible explanation for secretion.
- This mechanism integrates vesicular and constitutive secretion pathways.
- Porocytosis aligns with all available physiological observations.