Methods of increasing CFTR activity in a cell, comprising contacting the cell with a peptide modulator of CFTR to thereby increase CFTR activity in the cell. Methods of treating cystic fibrosis in a subject in need thereof, comprising administering an effective amount of a peptide modulator of CFTR to the subject to thereby increase CFTR activity in the subject. Pharmaceutical compositions comprising a peptide modulator of CFTR. The peptide modulator may comprise or consist of an amino acid fragment of the CB subunit of crotoxin from Crotalus durrissus terrificus venom. The peptide modulator may comprise or consist of the amino acid sequence of SEQ ID NOS: 1, 2, 3, 4, 5 or 6.
