Effect of stretch on passive transport in toad urinary bladder

Area of Science:

• Physiology
• Urothelial Biology
• Membrane Transport

Background:

• The urinary bladder's response to stretch is crucial for regulating fluid and electrolyte balance.
• Understanding how mechanical forces influence solute and water transport is key to bladder function.

Purpose of the Study:

• To investigate the impact of acute volume changes (stretch) on toad urinary bladder permeability to sucrose, chloride, and urea.
• To assess the relationship between bladder stretch, short-circuit current (SCC), and tissue conductance (Kt).

Main Methods:

• Measurement of transepithelial movement of radioactive sucrose, chloride, and urea across toad bladder sacs.
• Simultaneous recording of short-circuit current (SCC) and total tissue conductance (Kt) under varying internal volumes.
• Calculation of total diffusion (TD) by normalizing tracer permeability for surface area changes.

Main Results:

• Stretch-induced changes in calculated tracer permeability (P*) were attributed to alterations in surface area, not actual solute movement.
• Total diffusion (TD) of sucrose, chloride, and urea remained unaffected by bladder stretch.
• Increased bladder volume led to parallel increases in SCC and Kt, indicating enhanced ion transport.

Conclusions:

• Bladder stretch does not significantly alter the permeability of intercellular (sucrose, chloride) or transcellular (urea) pathways.
• Increased tissue conductance (Kt) during stretch likely reflects changes in active pathway conductance (Ka).
• Stretch-mediated increases in Kt may be linked to enhanced sodium transport in the toad urinary bladder.