Difference Between Constitutive and Regulated Exocytosis

The key difference between constitutive and regulated exocytosis is that in constitutive exocytosis, secretory materials are continuously released, while in regulated exocytosis, secretory materials are stably accumulated in secretory vesicles as storage sites.

Exocytosis is the process by which cells release molecules to the outside of the cell. By exocytosis, cells transport molecules to the plasma membrane and many cells also release proteins to the extracellular fluid. In addition, cells communicate with each other via a variety of signalling molecules. Intracellular signalling molecules are released by secretory vesicles. There are two types of exocytosis as constitutive exocytosis and regulated exocytosis. Cells carry out constitutive exocytosis to transfer molecules from the Golgi network to the outer surface of the cell. In constitutive exocytosis, secretory materials are continuously released. On the other hand, cells carry out regulated exocytosis in response to specific conditions, signals or biochemical triggers. In regulated exocytosis, secretory materials are released in a highly regulated manner into secretory vesicles.

1. Overview and Key Difference
2. What is Constitutive Exocytosis
3. What is Regulated Exocytosis
4. Similarities Between Constitutive and Regulated Exocytosis
5. Side by Side Comparison – Constitutive vs Regulated Exocytosis in Tabular Form
6. Summary

What is Constitutive Exocytosis?

Constitutive exocytosis is one of the two types of exocytosis. Cells carry out constitutive exocytosis in order to transfer molecules from the Golgi network to the external environment of the cell. It is the default pathway of exocytosis, and it is important in transporting proteins like receptors that function in the plasma membrane.

Difference Between Constitutive and Regulated Exocytosis

Figure 01: Constitutive vs Regulated Exocytosis

Moreover, in constitutive exocytosis, secretory materials are released continuously. The rate of constitutive exocytosis is well controlled. This rate depends on their rate of production, which is regulated by transcription and translation. But unlike regulated exocytosis, secretory materials are not released in a regulated manner.

What is Regulated Exocytosis?

Regulated exocytosis is a more specialized form of exocytosis that is triggered when a cell receives a signal from the outside. Cells carry out regulated exocytosis in response to specific conditions, signals or biochemical triggers. Cells release materials in a highly regulated manner. Secretory materials are first accumulated in secretory vesicles in regulated exocytosis. In this way, cells release cytokines, hormones, neurotransmitters, neuropeptides and other small signalling molecules.

Key Difference - Constitutive vs Regulated Exocytosis

Figure 02: Regulated Exocytosis

Regulated exocytosis forms the basis for many intercellular signalling processes. There are two pathways of regulated exocytosis. The first pathway primarily secretes polypeptides while the second pathway primarily secretes low-molecular-weight substances.

What are the Similarities Between Constitutive and Regulated Exocytosis?

Constitutive and regulated exocytosis are two types of exocytosis.
The fundamental pathway and the basic mechanism for regulated and constitutive exocytosis are similar.

What is the Difference Between Constitutive and Regulated Exocytosis?

Exocytosis can be constitutive or regulated. In constitutive exocytosis, secretory materials are released continuously. But, in regulated exocytosis, secretory materials are released into secretory vesicles on-demand via secretagogues and signal transduction. So, this is the key difference between constitutive and regulated exocytosis.

More differences between constitutive and regulated exocytosis are shown in tabular form in the below infographic.

Summary – Constitutive vs Regulated Exocytosis

Constitutive and regulated exocytosis are two types of exocytosis. In constitutive exocytosis, secretory materials are released continuously. Secretagogue or storage vesicles are not involved. It is important in transporting proteins like receptors that function in the plasma membrane. On the other hand, regulated exocytosis occurs in a regulated manner. Secretory materials are released via secretory vesicles. It is triggered when a cell receives a signal from the outside. The release of cytokines, hormones, neurotransmitters and other small signalling molecules takes place through regulated exocytosis. Thus, this is the summary of the difference between constitutive and regulated exocytosis.

Reference:

1. Gerber, Stefan H., and Thomas C. Südhof. “Molecular Determinants of Regulated Exocytosis.” Diabetes, American Diabetes Association, 1 Feb. 2002, Available here.
2. Alberts, Bruce. “Transport from the Trans Golgi Network to the Cell Exterior: Exocytosis.” Molecular Biology of the Cell. 4th Edition., U.S. National Library of Medicine, 1 Jan. 1970, Available here.