Nature of Secretory Potentials
Any excitation of secretory cells is inextricably linked to changes in their membrane charge. The resulting secretory potentials are not identical across all types of glandular tissues.
Depending on the specific cell type, the membrane potential may change in two opposite directions:
- Depolarization — a decrease in the level of membrane polarization (typical for one group of cells).
- Hyperpolarization — an increase in the membrane charge (observed in other cell types).
Both variants of membrane potential changes serve a single purpose: triggering the cascade of reactions that leads to the release of the synthesized product.
Intracellular Electrical Field
A key factor in intracellular transport is spatial charge asymmetry. The basal membrane (base of the cell) and the apical membrane (its apex) exhibit differing degrees of polarization.
This difference creates the cell's own electrical field. Its main characteristics are:
- At rest, the potential difference between the poles creates a field with a voltage of 20–30 mV.
- At the moment of cell excitation, the voltage of this electrical field doubles (reaching 40–60 mV).
The function of the electrical field is to provide directed transport. The increased voltage promotes the active movement of mature secretory granules. They are directed toward the apical pole of the cell, where they interact directly with the cell membrane for subsequent release.
Mechanisms of Secretion Release
After the electrical field has transported the mature granules to the apical membrane and facilitated their interaction, the final stage occurs—the release of the substance outward.
According to physiological mechanisms, secretion release can occur through two main pathways:
- Diffusion — passive penetration of secretory molecules through the membrane.
- Exocytosis — an active process of fusion between the secretory granule and the cell membrane, releasing its contents into the extracellular space.