Sodium transport in basolateral membrane vesicles from rat enterocytes.

Area of Science:

• Cell Biology
• Physiology
• Biochemistry

Background:

• Basolateral membranes from rat jejunal enterocytes are crucial for nutrient absorption and ion transport.
• These membranes are enriched in (Na, K)-ATPase, a key player in maintaining cellular ion gradients.

Purpose of the Study:

• To investigate the mechanisms of sodium (Na) transport across the basolateral membrane of rat jejunal enterocytes.
• To characterize the role of ATP and potassium (K) in modulating Na transport.
• To identify distinct Na transport systems, including the (Na, K)-ATPase and other carriers.

Main Methods:

• Purification of basolateral membranes from rat jejunal enterocytes.
• Preparation of inside-out (IO) and right-side-out (RSO) vesicles.
• Measurement of Na+ influx using a rapid filtration technique under various conditions (presence/absence of ATP, K+).
• Assessment of (Na, K)-ATPase activity and modulation by inhibitors (vanadate, strophanthidin) and enhancers (bleomycin).

Main Results:

• Sodium transport is mediated by both the (Na, K)-ATPase (Na pump) and a separate carrier-mediated system.
• The carrier-mediated Na transport is trans-stimulated by K+ and cis-inhibited by K+.
• ATP significantly stimulates Na transport, an effect inhibited by vanadate and strophanthidin.
• Bleomycin enhances both (Na, K)-ATPase activity and overall Na transport.
• No evidence for Na-K cotransport was found.

Conclusions:

• Rat jejunal basolateral membranes possess at least two distinct Na transport mechanisms: the (Na, K)-ATPase and a K+-stimulated carrier.
• These findings elucidate the complex regulation of Na+ homeostasis in intestinal epithelial cells.
• The study differentiates the roles of the Na pump and other Na carriers in basolateral transport.