Exploring Intestinal Ion Transport Mechanisms: Insights from the EasyMount Ussing Chamber and Hydrogen Sulfide Research

Hydrogen Sulfide Triggering Secretion

This study explores how hydrogen sulfide (H₂S) triggers secretion in the intestines, focusing on the mechanisms and pathways involved. H₂S, a gasotransmitter, is known for its role in regulating various physiological processes and its potential therapeutic uses. Researchers investigated the effects of an H₂S donor compound, NaHS, on guinea-pig and human colonic tissues using specialized techniques to measure secretion and nerve activity.

The results revealed that NaHS-induced secretion is primarily mediated by TRPV1, a receptor found on certain sensory nerves. When activated by H₂S, these nerves release the neurotransmitter substance P, which then stimulates cholinergic neurons responsible for secretion. Blocking TRPV1 with specific inhibitors like capsazepine and AMG9801 significantly reduced the secretion, underscoring the receptor’s crucial role.

Intracellular signaling pathways, including calcium and phosphatidylinositol-3 kinase (PI3K), were also found to contribute to the pro-secretory effects of H₂S. Inhibitors targeting these pathways diminished NaHS responses, further linking them to the process. Additionally, the study demonstrated that TRPV1 activation by H₂S overlaps with its activation by capsaicin, a known TRPV1 stimulant, as both substances showed cross-desensitization effects.

Interestingly, not all TRP channels were involved. TRPA1 and TRPC channels, blocked using specific inhibitors, did not appear to mediate the effects of H₂S in guinea pigs. However, in human tissues, gadolinium, a TRPC blocker, reduced H₂S-induced secretion, suggesting species-specific differences. The study also found that substance P activates neurokinin receptors in the intestines, but the specific receptor types varied between species. In guinea pigs, NK1 and NK3 receptors were involved, while in humans, NK1 and NK2 receptors played a role. This variation highlights the complexity of H₂S signaling across different systems.

Ruthenium red, a TRPV1 pore blocker, had mixed effects depending on the NaHS concentration, reducing secretion at low levels but amplifying it at high levels. These findings suggest multiple ways in which H₂S interacts with TRPV1, including potential direct binding to different sites on the receptor.

In summary, H₂S promotes intestinal secretion by activating TRPV1 receptors on sensory nerves and triggering downstream signaling pathways, including substance P release and intracellular calcium increases. These insights into H₂S’s role as a natural modulator of intestinal function could inform new treatments for gastrointestinal disorders.

EasyMount Chambers used in this experiment

What we find fascinating is the EasyMount Ussing Chambers were used in this study to examine how the H₂S donor compound NaHS affects ion secretion in guinea-pig and human colonic tissues. The chambers allowed researchers to measure the transepithelial short-circuit current (I_sc), a marker of electrogenic ion transport, which reflects secretion in the tissue. Here’s a detailed account of their use:

1. Tissue Preparation: Mucosa/submucosa layers from guinea-pig and human intestines were isolated to preserve their functional submucosal nerve plexus. These tissues were mounted in the EasyMount chambers, which securely hold the samples for experimentation.
2. Chamber Setup: The mucosal (luminal) and serosal (basolateral) sides of the tissue were bathed in separate compartments with a Krebs solution maintained at 37°C. The solution was oxygenated to mimic physiological conditions.
3. Electrical Stimulation and Measurement: Electrodes in the chambers allowed researchers to deliver electrical pulses to stimulate nerve activity and measure the resulting I_sc. Changes in the current reflected ion movement, particularly chloride, indicative of secretion levels.
4. Drug Application: Various compounds, including NaHS (the H₂S donor) and specific inhibitors, were applied to the serosal side to evaluate their effects on secretion. For instance, TRPV1 blockers and other inhibitors were added to determine their impact on the NaHS-induced secretion.
5. Analysis: By comparing I_sc responses before and after applying NaHS and other substances, the researchers could identify the pathways and receptors involved in the secretion process. A significant reduction in I_sc following the addition of inhibitors pinpointed specific mechanisms.

The EasyMount Ussing Chambers provided a controlled environment to study ion transport in real-time, enabling precise assessment of how NaHS drives secretion through neural and molecular pathways in the intestines.

To view the original paper click this link:  Signaling mechanisms involved in the intestinal pro-secretory actions of hydrogen sulfide