[Ultrastructure of the apical plasma membrane of the granular cells in the frog bladder during cobalt-ion decrease in...

Area of Science:

• Cell Biology
• Physiology
• Membrane Biophysics

Background:

• The frog urinary bladder epithelium is crucial for water reabsorption.
• Vasopressin stimulates water flow by altering apical membrane permeability.
• The role of extracellular ions in regulating this process requires further investigation.

Purpose of the Study:

• To investigate the effect of cobalt ions (Co-ions) on water permeability.
• To examine the ultrastructural changes in the apical membrane of granular cells under vasopressin stimulation in the presence of Co-ions.
• To determine if Co-ions inhibit vasopressin-stimulated water flow.

Main Methods:

• Simultaneous measurements of water permeability and ultrastructural organization.
• Freeze-fracture technique to analyze the apical membrane.
• Application of Cobalt Chloride (CoCl2) from the mucose side.

Main Results:

• Vasopressin-stimulated water flow was inhibited by CoCl2 (1 x 10(-3)-1 x 10(-4) M).
• Freeze-fracture revealed a reduction in intramembrane particle aggregates on the P-face of the apical membrane.
• The percentage of membrane area occupied by aggregates decreased from 1.8% to 0.3% with reduced water flow.

Conclusions:

• Cobalt ions influence the structure and function of the apical plasma membrane from its extracellular surface.
• Co-ions may inhibit water permeability by altering the organization of intramembrane particles.
• The findings suggest a mechanism for ion-mediated regulation of epithelial water transport.