Figure 4.

The ionic strength of the mucin barrier can regulate its selective properties. (a) Increasing ionic strength within the mucin barrier significantly increases penetration and transport of the cationic (ninefold increase in accumulation from 5 to 200 mM ionic strength), but only marginally increases transport of the anionic peptide. (b) Unlike the uniformly charged cationic and anionic peptides whose transport rates increased monotonically with ionic strength, the transport rate of the block peptide was highest at the intermediate ionic strength of 20 mM NaCl. The transport rate of the alternate peptide was not significantly affected by ionic strength, demonstrating that the influence of ionic strength on peptide transport depends on spatial distribution of change. (Movie S2 and Movie S3) (c and d) The transport rates of the individual peptide species relative to one another depend on the surrounding ionic strength. Hence, charge polarity and distribution may be tuned to maximize transport into mucus barriers at different anatomical locations with varying ionic environments. n ≥ 3 for each peptide and ionic strength combination.