Resting and osmotically induced basolateral K conductances in turtle colon

Area of Science:

• Cellular Physiology
• Ion Transport
• Epithelial Biology

Background:

• Colonic epithelial cells exhibit distinct basolateral potassium (K+) conductances.
• The functional significance of these conductances, particularly under osmotic stress, requires elucidation.

Purpose of the Study:

• To investigate the role of two K+ conductances in colonic epithelial cells under varying osmotic conditions.
• To differentiate K+ conductance mechanisms activated during normal transport versus extreme cell swelling.

Main Methods:

• Utilized polyene-treated colonic epithelial cell layers.
• Measured basolateral membrane conductance under osmotic stress induced by permeant solutes (KCl, urea, benzene sulfonate) and impermeant solutes (K-gluconate, sucrose).
• Assessed K+ selectivity and sensitivity to quinidine and lidocaine.

Main Results:

• Permeant solutes and benzene sulfonate induced quinidine-sensitive K+ conductance and significant cell swelling.
• Impermeant solutes did not activate this quinidine-sensitive conductance despite cell volume changes.
• Extreme osmotic stress activated a novel K+ conductance, highly selective for K+ over Rb+ and blocked by quinidine/lidocaine.

Conclusions:

• A quinidine-sensitive basolateral K+ conductance is activated under conditions of extreme osmotic stress and cell swelling.
• This swelling-activated conductance differs from the K+ channels involved in normal colonic epithelial transport.
• These findings reveal a distinct ion channel mechanism responding to severe cellular osmotic challenges.