Pathways for K+ efflux in isolated surface and crypt colonic cells. Activation by calcium

Area of Science:

• Cellular Physiology
• Ion Transport Mechanisms
• Gastrointestinal Biology

Background:

• Understanding potassium (K+) transport is crucial for colonic function.
• Distinct K+ conductive pathways exist in colonic epithelial cells.
• The role of calcium-activated K+ channels in the colon requires further elucidation.

Purpose of the Study:

• To characterize K+ conductive pathways in isolated surface and crypt colonic cells.
• To identify the specific types of K+ channels involved in colonic K+ transport.
• To investigate the role of intracellular calcium in regulating these pathways.

Main Methods:

• Measurement of 86Rubidium (86Rb) efflux from isolated colonic cells.
• Pharmacological characterization using channel blockers like tetraethylammonium (TEA), barium (Ba2+), apamin, iberiotoxin, charybdotoxin, and clotrimazole.
• Stimulation of K+ efflux using ionomycin and manipulation of extracellular and intracellular calcium concentrations.

Main Results:

• Crypt cells exhibited basal K+ efflux sensitive to TEA and Ba2+, suggesting two pathways.
• Ionomycin stimulated K+ efflux in both cell types, primarily via Ca2+-activated intermediate-conductance K+ channels (IK(Ca)).
• IK(Ca) channel activation was dependent on intracellular calcium, with an EC50 of 1.1 µM.

Conclusions:

• Both surface and crypt colonic cells express IK(Ca) channels.
• Crypt cells possess additional TEA- and Ba2+-sensitive conductive pathways.
• These distinct pathways in crypt cells likely contribute to colonic K+ secretion.