Ionic mechanisms of Ca(2+)-dependent electrolyte transport across equine sweat gland epithelium.

The research investigates the mechanisms involved in electrolyte transport, specifically calcium-stimulated, in horse sweat gland cells. The findings indicate that calcium can trigger the secretion of chloride and bicarbonate ions in these cells, contributing to the processes of sweat production and ion balance.

Methods and Experimental Design

• The researchers studied equine sweat gland epithelial cells that were grown in a culture. They used a technique known as the short-circuit current technique to study the ionic mechanisms within these cells.
• The cultured cells were grown on Millipore filters which allowed the researchers to observe that they formed polarized monolayers with tight junctions. The monolayers exhibited a specific transepithelial resistance.
• Different agents that facilitate the mobilization of calcium ions—namely A23187 and thapsigargin—were applied. The researchers also tested the impact of forskolin, a commonly used tissue/cell research tool, and found it had minimal effect on the currents.

Findings on Chloride Replacement and Inhibitory Actions

• When external chloride ions were replaced by gluconate, the ISC decreased significantly, indicating a role of chloride ions in maintaining the cell current. Eliminating bicarbonate from the solution almost completely abolished the remaining ISC, thus demonstrating a critical role of bicarbonate as well.
• Other substances such as bumetanide, ouabain, acetazolamide, and methyl isobutyl amiloride were added to the cellular environment and were found to inhibit the ISC to varying degrees, showing the crucial role these chemicals play in the regulation of electrolyte transport in sweat gland cells.
• A stronger inhibitory effect could be achieved using DIDS and DPC, signifying that these chemicals can be used as powerful blockers of ionic activity within the sweat gland cells.
• The K+ channel blocker, barium, was effective on both sides of the epithelium but had a stronger effect on the basolateral side, indicating the presence of differently behaving K+ channels on different sides of the gland.

Conclusions

• The inhibitory effects of many substances on the thapsigargin-stimulated ISC were also observed when a chloride-free solution was used. This suggests a role of chloride on the surface of the cell.
• The overall results provide compelling evidence that calcium-stimulated bicarbonate and chloride secretion play a vital role in equine sweat gland function. This understanding is critical to further studies of sweat production and electrolyte balance in horses, which is of significant importance in equine health and performance.