Two modes of phosphate transport by turtle urinary bladder

Area of Science:

• Physiology
• Renal Physiology
• Ion Transport

Background:

• Transepithelial phosphate transport is crucial for maintaining phosphate homeostasis.
• The influence of pH and carbon dioxide/bicarbonate (CO2/HCO3-) on this transport is not fully understood.

Purpose of the Study:

• To investigate the effects of varying pH and CO2/HCO3- levels on phosphate transport across the turtle urinary bladder.
• To elucidate the specific phosphate species transported under different conditions.

Main Methods:

• Measurement of net mucosa-to-serosa phosphate flux (JP) using 32P in isolated turtle urinary bladders.
• Manipulation of pH and CO2/HCO3- concentrations in the bathing solutions.
• Assessment of the effects of ouabain and dinitrophenol on phosphate transport.

Main Results:

• At alkaline pH (8.4), phosphate transport (JP) was CO2/HCO3- independent and unaffected by ouabain or dinitrophenol, suggesting HPO4(2-) transport.
• At acidic pH (6.5), JP was significantly higher, CO2/HCO3- dependent, and inhibited by ouabain and dinitrophenol, indicating H2PO4- transport.
• Phosphate transport increased with phosphate concentration at alkaline pH.

Conclusions:

• Phosphate transport in turtle urinary bladder is pH-dependent, with distinct mechanisms operating at acidic and alkaline conditions.
• At acidic pH, the transport of H2PO4- is an active, CO2-dependent process.
• At alkaline pH, the transport of HPO4(2-) is a passive process, independent of CO2 and metabolic inhibitors.