Calcium-dependent chloride secretion in rat colon epithelium

Area of Science:

• Physiology
• Cell Biology
• Biophysics

Background:

• The descending rat colon's epithelial transport mechanisms are crucial for electrolyte balance.
• Short-circuit current (s.c.c.) measurements in Ussing chambers are a standard method for assessing epithelial ion transport.
• Photodynamic activation offers a potential tool to probe cellular signaling pathways.

Purpose of the Study:

• To investigate the photodynamic effects of erythrosine B on ion transport in rat colon epithelia.
• To elucidate the role of calcium, oxygen, and other ions in this photodynamic response.
• To characterize the specific ion flux changes induced by photodynamic activation.

Main Methods:

• Dissection of descending rat colon epithelia and mounting in modified Ussing chambers.
• Irradiation of tissues with white light in the presence of erythrosine B.
• Measurement of short-circuit current (s.c.c.) and ion fluxes (36Cl, 22Na).
• Manipulation of bathing solution composition (oxygen, calcium, cobalt, magnesium).

Main Results:

• Irradiation alone did not affect s.c.c.; erythrosine B plus irradiation significantly increased s.c.c. in an oxygen- and calcium-dependent manner.
• The photodynamic effect abolished net sodium absorption and reversed net chloride absorption to secretion.
• Cobalt and magnesium ions antagonized the calcium-mediated response.
• Chloride secretion was half-maximally activated at 1 microM ionized calcium, with a steep dose-response relationship.

Conclusions:

• Photodynamic activation of erythrosine B in rat colon epithelia stimulates electrogenic chloride secretion.
• This process involves the abolition of electroneutral sodium chloride absorption and is critically dependent on calcium and oxygen.
• The findings suggest a novel method for manipulating epithelial ion transport and provide insights into calcium signaling pathways.