Vasopressin-induced changes in the three-dimensional structure of toad bladder apical surface

Area of Science:

• Cell biology
• Membrane biophysics
• Epithelial physiology

Background:

• Toad bladder granular cells increase water permeability upon vasopressin stimulation.
• This involves apical plasma membrane morphological changes, potentially mediating the hormonal response.

Purpose of the Study:

• To investigate the mechanism of vasopressin-induced apical membrane morphological changes.
• To visualize the surface dynamics of toad bladder granular cells during vasopressin stimulation using high-resolution imaging.

Main Methods:

• Rapid freezing and freeze-drying techniques to capture high-resolution stereo images of the apical plasma membrane.
• Microscopic analysis of cell surface morphology before and during vasopressin stimulation.
• Assessment of the effects of cytochalasin D on membrane transformation.

Main Results:

• Vasopressin induces a ridge-to-villus transformation of the apical cell surface, primarily through retraction of existing ridges.
• This transformation occurs independently of osmotic water flow and is not prevented by cytochalasin D.
• The cell surface glycocalyx exhibits a complex, heterogeneous filamentous network.
• Vasopressin induces tubular invaginations, potentially representing exo/endocytotic events, with altered morphology in the presence of cytochalasin D.

Conclusions:

• Vasopressin-mediated water permeability increase involves significant apical membrane remodeling via ridge retraction.
• The findings suggest a mechanism for membrane trafficking and surface area modulation during hormonal stimulation.
• The study provides novel insights into the dynamic structural changes of the apical membrane in response to vasopressin.