. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 86 L. F. GAINEY ET AL LQG5HT(M1 RESPONSE -7 -6 -S -4 -3 -2 5 min Figure 3. Traces of contractions in response to increasing concentra- tions of 5HT; successive doses were added at the arrows. Each response is from a separate demibranch; data were recorded with force transducers. indistinguishable: the gills contracted tonically and, after 30 s to several minutes, reached their maxima. Dose-response curves for the three agonists were pre- pared (Fig. 4), and their characteristics are listed in Table 1. The rankings of the EC5
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 86 L. F. GAINEY ET AL LQG5HT(M1 RESPONSE -7 -6 -S -4 -3 -2 5 min Figure 3. Traces of contractions in response to increasing concentra- tions of 5HT; successive doses were added at the arrows. Each response is from a separate demibranch; data were recorded with force transducers. indistinguishable: the gills contracted tonically and, after 30 s to several minutes, reached their maxima. Dose-response curves for the three agonists were pre- pared (Fig. 4), and their characteristics are listed in Table 1. The rankings of the EC5() values are ACh < 5HT < DA, and since the 95% confidence intervals do not overlap, the values are statistically different. The maximal contractions in response to 5HT and DA are equal, and both are signif- icantly larger than the maximal contractions induced by ACh. The comparative data noted above were independent of the method used to record the contractions. However, if we consider each agonist separately, then its EC50 is signif- icantly less, and its induced contractions were larger (except for DA) when the contractions were recorded with the digital ultrasound system rather than with force transducers (Table I). The following neurotransmitters, all applied to the tissue at 1()~4 M. neither contracted nor relaxed the gills: ATP, GABA, histamine. and octopamine. Furthermore, the fol- lowing three peptides—all found in Mercrmiriti and all applied at 10~6 M—neither contracted nor relaxed the gills: FMRFamide, AMSFYFPRMamide, and YFAFPRQamide. Previously, we found that YFAFPRQamide modulates the effects of DA on the lateral cilia and those of 5HT on the frontal cilia (Gainey et 1999a). Therefore, to determine whether the peptide would modulate the effects of 5HT or : Ultrasound recorder • : Foree transducers : I :i * log |5HT(M) |. 0 -(. -5 -4 log|ACh(M)| Figure 4. Dose-dependent muscle contractions (as percentages of the resting length) in response to 5HT,
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