Mucosal histamine inhibits Na absorption and stimulates Cl secretion across equine tracheal epithelium.

This research aims to investigate how histamine, a compound involved in immune responses, affects sodium absorption and chloride secretion in the epithelial lining of horse trachea. The study works with conditions that mimic those inside the body and finds that histamine both inhibits sodium absorption and stimulates chloride secretion.

Experimental Procedure

• Equine tracheal epithelium tissues were set up in Ussing chambers and bathed in a Ringer solution that mimics the plasma environment found in the body.
• The tissues generated a negative electric potential (PD) across the epithelium and a baseline short-circuit current (Isc), a measure of net ion movement, which was observed.
• Histamine was then added to the sample, along with diphenhydramine and cimetidine, two types of antihistamines. The changes in the Isc were recorded.
• To further investigate the role of sodium in this process, amiloride, an inhibitor of sodium channels, was added to the sample.
• Finally, the effects of chloride were examined by replacing chloride with gluconate, a non-chloride ion, and measuring the resulting Isc. The use of bumetanide, a diuretic which inhibits chloride channels was also used to study effects on Chloride.

Findings

• The addition of histamine to the tissue drastically altered the Isc. However, these effects were reduced when the tissue was pretreated with diphenhydramine or cimetidine. This implies that histamine affects ion movement across the epithelium.
• When sodium absorption was inhibited by amiloride, the action of histamine was prolonged. This indicates that the process in some way involves sodium.
• Replacing chloride with gluconate decreased Isc and reduced the effect of amiloride on Isc, suggesting that chloride ions play a pivotal role in the process as well.
• The experiment showed that histamine inhibited the overall movement of positively charged sodium ions while stimulating the movement of negatively charged chloride ions.
• The addition of bumetanide revealed that the chloride secretion stimulated by histamine was sensitive to this inhibitor, confirming the role of histamine in chloride secretion.

Conclusion

• The work concluded that histamine has a role in moving ions across the epithelium and does so by inhibiting the absorption of sodium and stimulating the secretion of chloride. These effects are mediated through H1 receptors on the apical surface of the cells.