β-defensin-2 in breast milk displays a broad antimicrobial activity against pathogenic bacteria.

Objective: To describe the antimicrobial activity of β-defensin-2 produced in the mammary gland and secreted in human breast milk.

Methods: The peptide production was performed by DNA cloning. β-defensin-2 levels were quantified in 61 colostrum samples and 39 mature milk samples from healthy donors, by an indirect enzyme-linked immunosorbent assay (ELISA).

Is the second sodium pump electrogenic?

Transepithelial sodium transport is a process that involves active Na(+) transport at the basolateral membrane of the epithelial cell. This process is mediated by the Na(+)/K(+) pump, which exchanges 3 internal Na(+) by 2 external K(+) inducing a net charge movement and the second Na(+) pump, which transports Na(+) accompanied by Cl(-) and water. It has been suggested that this pump could also be electrogenic.

The second sodium pump: from the function to the gene.

Transepithelial Na(+) transport is mediated by passive Na(+) entry across the luminal membrane and exit through the basolateral membrane by two active mechanisms: the Na(+)/K(+) pump and the second sodium pump. These processes are associated with the ouabain-sensitive Na(+)/K(+)-ATPase and the ouabain-insensitive, furosemide-inhibitable Na(+)-ATPase, respectively. Over the last 40 years, the second sodium pump has not been successfully associated with any particular membrane protein.

Isolation and cloning of the K+-independent, ouabain-insensitive Na+-ATPase.

Primary Na+ transport has been essentially attributed to Na+/K+ pump. However, there are functional and biochemical evidences that suggest the existence of a K+-independent, ouabain-insensitive Na+ pump, associated to a Na+-ATPase with similar characteristics, located at basolateral plasma membrane of epithelial cells. Herein, membrane protein complex associated with this Na+-ATPase was identified.

Purification and characterization of the ouabain-sensitive H+/K+-ATPase from guinea-pig distal colon.

Distal colon absorbs K+ through a Na+-independent, ouabain-sensitive H+/K+-exchange, associated to an apical ouabain-sensitive H+/K+-ATPase. Expression of HKalpha2, gene associated with this ATPase, induces K+-transport mechanisms, whose ouabain susceptibility is inconsistent. Both ouabain-sensitive and ouabain-insensitive K+-ATPase activities have been described in colonocytes.