Do isolated gastric mucosal surface cells from rabbits secrete HCO3-?

Area of Science:

• Physiology
• Cell Biology
• Gastroenterology

Background:

• Gastric surface cells' role in bicarbonate (HCO3-) secretion for pH regulation is indirectly observed.
• Understanding intracellular pH (pHi) control mechanisms is crucial for gastric mucosal health.

Purpose of the Study:

• To investigate the significance of bicarbonate (HCO3-) transport in the intracellular pH (pHi) regulation of isolated gastric surface cells.
• To determine if gastric surface cells are a primary source of HCO3- secretion.

Main Methods:

• Isolated gastric surface cells were perfused with various solutions, including bicarbonate-free Ringer's, solutions with added bicarbonate/CO2, and inhibitors.
• Cellular pH changes were monitored during perfusion.
• Inhibitors used included 4,4'-diisothiocyanostilbene-2-2'-disulfonate (DIDS) for HCO3- transport and amiloride for Na+/H+ exchange.
• Acetazolamide was used to assess carbonic anhydrase activity.

Main Results:

• Cellular pH maintenance in bicarbonate-free solution was not affected by Cl- absence or DIDS, suggesting no significant Cl-/HCO3- exchange or Na+-related HCO3- transport.
• Addition of bicarbonate/CO2 caused initial acidification, followed by upward pH drift inhibited by amiloride, indicating Na+/H+ exchange involvement.
• Removal of bicarbonate/CO2 induced alkalinization, impaired by acetazolamide, pointing to carbonic anhydrase activity.
• Alkalinization was sustained by an extracellular Na+ gradient, preventing intracellular Na+ and extracellular H+ exchange, an effect blocked by amiloride.

Conclusions:

• Isolated gastric mucosal surface cells do not appear to be a major source of bicarbonate (HCO3-) secretion.
• Cellular alkalinization can be attributed to carbonic anhydrase activity.
• The maintenance of alkalinization relies on extracellular Na+ gradients, not direct HCO3- transport mechanisms.