AN ENDOGENOUS SCP-RELATED PEPTIDE MODULATES CILIARY BEATING IN THE GILLS OF A VENERID CLAM, MERCENARIA MERCENARIA

The activities of both the lateral and frontal cilia of Mercenaria mercenaria were unaffected, either by the two endogenous SCP-related peptides AMSFYFPRMamide and YFAFPRQamide, or by FMRFamide (all at 10-6 M). Dopamine (DA) inhibited the lateral cilia; the mean EC50 was 2 x 10-6 M. The peptide YFAFPRQamide--but neither AMSFYFPRMamide nor FMRFamide--antagonized the inhibition induced by DA; this effect was dependent on both time and dose. At a DA concentration of 5 x 10-7 M, the effect of YFAFPRQamide appeared within 20 min and became maximal within 40-60 min; the mean EC50 at these times was 4.7 x 10-11 M. If the concentration of DA was increased to 10-6 M, the maximal effect of the peptide was delayed to 50 min, and the mean EC50 increased to 1.1 x 10-7 M. Particle transport by the frontal cilia was inhibited by 5-hydroxytryptamine (5HT); the mean EC50 was 5.7 x 10-7 M. Again, only YFAFPRQamide had an antagonistic effect on the 5HT-induced inhibition. At a 5HT concentration of 10-6 M, the effects of YFA...