Figure 3. The FMRFamide-like peptide (FLP)-induced contractions are sensitive to classical voltage-operated Ca²⁺ channel (VOCC) blockers.

Although it required relatively high concentrations, the FLP-induced contractions were significantly blocked by the dihydropyridine nicardipine, as well as the phenylalkylamines verapamil and methoxyverpamil, but not by the benzothiazipine diltiazem. The potency and the rank order of efficacy of these VOCC blockers is the same as have been reported previously for the blockade of depolarization-induced contractions: nicardipine > verapamil ≈ methoxyverapamil >>> diltiazem. The drugs were added 15 min before testing with 1 µM YIRFamide. Data points represent the mean ± SEM of % muscle fibers contracting, with n≥5 for each point. **P<0.01, ***P<0.005.