. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. Peak Four. OJD 1 niin Figure 7. Cardioexcitatory effects of partially purified extracts of the Limulus prosomal CNS. Aliquots from each of the four peaks from the third HPLC run were tested on the intact heart preparation. Peaks one and two, which eluted near FMRFamide and TNRNFLRFamide respectively, promoted the greatest chronotropic excitation. tencies of these peptides on heart rate and contractile force were quite similar, suggesting that Limulus cardiac ganglion neurons and cardiac muscle fibers possess similar, FaRP-li
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. Peak Four. OJD 1 niin Figure 7. Cardioexcitatory effects of partially purified extracts of the Limulus prosomal CNS. Aliquots from each of the four peaks from the third HPLC run were tested on the intact heart preparation. Peaks one and two, which eluted near FMRFamide and TNRNFLRFamide respectively, promoted the greatest chronotropic excitation. tencies of these peptides on heart rate and contractile force were quite similar, suggesting that Limulus cardiac ganglion neurons and cardiac muscle fibers possess similar, FaRP-like receptors. Because TNRNFLRF- amide, SDRNFLRFamide, GYNRSFLRFamide, and pQDPFLRFamide all had excitatory effects, whereas RNFLRFamide was a weak agonist, we suggest that the FLRFamide sequence must be extended at the N terminus by at least three amino acids for full activation of FaRP receptors in the cardiac ganglion and in cardiac muscle. Similar N-terminal structural requirements for chrono- tropic excitation of the neurogenic heart of the blue crab Callinectes have been reported (Krajniak, 1991), and in both this species and Limulus, amino acid substitutions at the N-terminus are less restrictive than are extensions. Unlike Limulus, however, the Callinectes heart does not respond to low doses of pQDPFLRFamide (Krajniak and Greenberg, 1988). This heptapeptide, first isolated from the pulmonate mollusk Helix (Price el til., 1985), is more potent than FMRFamide on the heart of that species, as we observed with the neurogenic heart of Limulus. These findings suggest that the structure-activity characteristics of the FaRP receptors in Limulus, crustaceans, and mol- lusks are similar. Endogenous cardioactive FaRPs in Limulus Reverse phase HPLC indicates that several factors with FaRP-like bioactivity and immunoreactivity are present in the Limulus nervous system. Peak one, which increases heart contraction rate, has an elution time near that of synthetic FMRFamide, which is ina
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
