Aggregate-carrying membranes during ADH stimulation and washout in toad bladder

Area of Science:

• Cell biology
• Membrane trafficking
• Kidney physiology

Background:

• Aggrephores are cytoplasmic structures containing intramembrane particle aggregates.
• Antidiuretic hormone (ADH) induces aggrephore fusion with the luminal membrane, creating water channels.

Purpose of the Study:

• To investigate the behavior and dynamics of aggrephores in response to ADH stimulation and osmotic conditions.
• To elucidate the mechanisms of aggrephore fusion, detachment, and potential degradation.

Main Methods:

• Stimulation of bladder tissue with ADH under varying osmotic gradients.
• Microscopic analysis of aggrephore fusion and distribution.
• Use of horseradish peroxidase to trace aggrephore lumen.
• Treatment with colchicine and cytochalasin B to assess cytoskeletal involvement.

Main Results:

• Aggrephore fusion frequency is higher without an osmotic gradient, indicating influence by water flow.
• ADH stimulation does not alter luminal surface area; aggregates move to other membrane regions.
• Aggrephores detach from the luminal membrane during ADH washout and may transform into lysosomes.
• Cytochalasin B, but not colchicine, slows aggrephore detachment, implicating microfilaments.

Conclusions:

• Aggrephore fusion and water transport are modulated by osmotic flow.
• Aggrephores undergo dynamic membrane trafficking, including detachment and potential lysosomal transformation.
• Microfilaments play a role in the detachment of aggrephores from the luminal membrane.