Anion secretion evoked by Pasteurella multocida toxin across rat colon

Area of Science:

• Gastroenterology
• Molecular Biology
• Cell Signaling

Background:

• Muscarinic receptor stimulation causes biphasic colonic chloride secretion: initial activation followed by inhibition.
• The precise role of Gq proteins in these dual secretory processes remains unclear.

Purpose of the Study:

• To investigate the role of Gq proteins in both the activation and inhibition of colonic chloride secretion.
• To elucidate the signaling pathways involved in Gq protein-mediated intestinal secretion.

Main Methods:

• Utilized Pasteurella multocida toxin, a specific G alpha q activator, on rat distal colon models.
• Measured short-circuit current (Isc) to quantify chloride secretion.
• Employed inactive toxin mutants and specific G alpha q blockers (YM-254890) to confirm pathway involvement.
• Assessed basolateral potassium conductance changes in apically permeabilized tissues.

Main Results:

• Pasteurella multocida toxin demonstrated a dual effect: transiently stimulating Isc and subsequently down-regulating secretion induced by acetylcholine or ATP.
• The toxin's effects were confirmed to be chloride secretion-dependent and blocked by YM-254890, indicating G alpha q involvement.
• Secretory response to the toxin correlated with increased basolateral K+ conductance, similar to other Ca2+-dependent secretagogues.
• An inactive toxin mutant lacking G alpha q activating ability was ineffective.

Conclusions:

• Gq proteins are crucial for the initial activation of colonic secretion, as seen with muscarinic and purinergic receptor agonists.
• Gq proteins play a significant role in the long-lasting inhibition of intestinal secretion following receptor activation.
• These findings highlight the dual role of Gq proteins in regulating intestinal secretory dynamics.