Secretion without membrane fusion: Porocytosis

Robert B. Silver, George D. Pappas

Research output: Contribution to journalReview articlepeer-review

9 Scopus citations

Abstract

We have recently proposed a mechanism to describe secretion, a fundamental process in all cells. That hypothesis, called porocytosis, embodies all available data and encompasses both forms of secretion, i.e., vesicular and constitutive. The current accepted view of exocytotic secretion involves the physical fusion of vesicle and plasma membranes; however, that hypothesized mechanism does not fit all available physiological data. Energetics of apposed lipid bilayers do not favor unfacilitated fusion. We consider that calcium ions (e.g., 10-4 to 10-3 M calcium in microdomains when elevated for 1 ms or less), whose mobility is restricted in space and time, establish salt bridges among adjacent lipid molecules. This establishes transient pores that span both the vesicle and plasma membrane lipid bilayers; the diameter of this transient pore would be ∼ 1 nm (the diameter of a single lipid molecule). The lifetime of the transient pore is completely dependent on the duration of sufficient calcium ion levels. This places the porocytosis hypothesis for secretion squarely in the realm of the physical and physical chemical interactions of calcium and phospholipids and places mass action as the driving force for release of secretory material. The porocytosis hypothesis that we propose satisfies all of the observations and provides a framework to integrate our combined knowledge of vesicular and constitutive secretion.

Original languageEnglish (US)
Pages (from-to)18-37
Number of pages20
JournalAnatomical Record - Part B New Anatomist
Volume282
Issue number1
DOIs
StatePublished - Jan 1 2005
Externally publishedYes

Keywords

  • Constitutive secretion
  • Membrane fusion
  • Plasma membrane
  • Porocytosis
  • Quantal release
  • SNARE
  • Vesicular secretion

ASJC Scopus subject areas

  • Anatomy
  • Agricultural and Biological Sciences (miscellaneous)

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