Myotropic activity of tick pyrokinin neuropeptides and a pyrokinin analog in feeding tissues of hard ticks (Ixodidae).

G protein-coupled receptors of small neuropeptide ligands are considered promising targets for controlling arthropod pests. We are exploring the tick pyrokinin receptor as such a target. Pyrokinins (PKs) are pleiotropic neuropeptides that in some insect species stimulate muscle contraction, and modulate pheromone biosynthesis, embryonic diapause and feeding behavior. However, their function remains unknown in ticks. We report the myotropic activity of tick endogenous PKs and a PK agonist analog, PK-PEG₈ (MS[PEG₈]-YFTPRLa), on feeding tissues of two tick species representing the two Ixodidae lineages, Prostriata (Ixodes scapularis) and Metastriata (Rhipicephalus sanguineus). First, we analyzed the sequence of the CAPA peptide precursor from R. sanguineus and predicted it encodes two periviscerokinins (PVKs), one with a derived ending RNa instead of the canonical RVa, and five PKs. These PKs were identical to those of R. microplus we identified previously. The pharynx-esophagus of both tick species responded with increased contractions to 10 μM of the endogenous PK as well as to PK-PEG₈ but not to the scrambled PK peptide, as expected. A dose-dependent myotropic activity of the PK-PEG₈ was found for both tick species, validating the analog activity previously found on the pyrokinin recombinant receptor. We then quantified the relative transcript abundance of R. sanguineus PK receptor in unfed female ticks and found it was highest in the feeding tissues extracted from the capitulum, in agreement with the tissue activity elicited by PKs. This is the first report on the activity of pyrokinins in ticks.