Identification of a calcitonin-like diuretic hormone that functions as an intrinsic modulator of the American lobster,Homarus americanus, cardiac neuromuscular system

Abstract

SUMMARYIn insects, a family of peptides with sequence homology to the vertebrate calcitonins has been implicated in the control of diuresis, a process that includes mixing of the hemolymph. Here, we show that a member of the insect calcitonin-like diuretic hormone (CLDH) family is present in the American lobster, Homarus americanus, serving, at least in part, as a powerful modulator of cardiac output. Specifically, during an ongoing EST project, a transcript encoding a putative H. americanus CLDH precursor was identified; a full-length cDNA was subsequently cloned. In silico analyses of the deduced prepro-hormone predicted the mature structure of the encoded CLDH to be GLDLGLGRGFSGSQAAKHLMGLAAANFAGGPamide (Homam-CLDH), which is identical to a known Tribolium castaneum peptide. RT-PCR tissue profiling suggests that Homam-CLDH is broadly distributed within the lobster nervous system, including the cardiac ganglion (CG), which controls the movement of the neurogenic heart. RT-PCR analysis conducted on pacemaker neuron-and motor neuron-specific cDNAs suggests that the motor neurons are the source of the CLDH message in the CG. Perfusion of Homam-CLDH through the isolated lobster heart produced dose-dependent increases in both contraction frequency and amplitude and a dose-dependent decrease in contraction duration, with threshold concentrations for all parameters in the range 10 -11 to 10 -10 moll -1 or less, among the lowest for any peptide on this system. This report is the first documentation of a decapod CLDH, the first demonstration of CLDH bioactivity outside the Insecta, and the first detection of an intrinsic neuropeptide transcript in the crustacean CG.

Distinct or shared actions of peptide family isoforms: I. Peptide-specific actions of pyrokinins in the lobster cardiac neuromuscular system

“…Christie, 2011;Christie et al, 2010a). Local sources of neuromodulators include the cardiac pacemaker and motor neurons themselves [glutamate in the former (Delgado et al, 2000) and a member of the calcitonin-like diuretic hormone/diuretic hormone 31 peptide family in the latter (Christie et al, 2010b)], and axons of projection neurons whose somata are located elsewhere in the nervous system (Cooke, 2002), which are the local sources of at least GABA (Delgado et al, 2000) and dopamine (Fort et al, 2004). The neuroendocrine pericardial organ, which surrounds the heart and the X-organ-sinus gland (XO-SG) complex, located in the eyestalks, are the primary sources of the hemolymph-borne neuromodulators that influence the cardiac CPG-effector system (Christie, 2011).…”

The peptide hormone pQDLDHVFLRFamide (crustacean myosuppressin) modulates theHomarus americanuscardiac neuromuscular system at multiple sites

“…The best-documented intrinsic source of modulation is nitric oxide, which appears to be synthesized in the cardiac muscle (Mahadevan et al, 2004) and diffuses to the CG, where it causes a decrease in cycle frequency. A second intrinsic modulator, Homarus americanus calcitonin-like diuretic hormone (Homam-CLDH), has recently been identified (Christie et al, 2010). The transcript for this peptide hormone, which strongly activates cardiac activity, is present within the motor neurons of the CG.…”

Forces generated during stretch in the heart of the lobsterHomarus americanusare anisotropic and are altered by neuromodulators

“…The signals from the force transducers were amplified by a Model 44 Brownlee Precision Instrumentation amplifier and recorded with a Cambridge Electronic Design (CED) Micro 1401 digitizer paired with Spike2 version 7.03 software (CED, Cambridge, UK). The output of the force transducer is reported in grams rather than Newtons for consistency with other studies that have studied single locations on the length-tension curve (Fort et al, 2004(Fort et al, , 2007aStevens et al, 2009;Christie et al, 2010b;Dickinson et al, 2015).…”

“…Although the effects of neuromodulators on crustacean CPGeffector systems are well documented, these studies have only examined the physiological effects at single locations on the lengthtension curve (Mercier and Russenes, 1992;Fort et al, 2004;Wilkens et al, 2005;Fort et al, 2007a,b;Stevens et al, 2009;Christie et al, 2010b;Dickinson et al, 2015). However, it is important to consider the functional space in which the neurotransmitters are working.…”