FMRFamide-Activated Ca2+ Channels in Lymnaea Heart Cells Are Modulated by "SEEPLY," a Neuropeptide Encoded on the Same Gene

• Published in: Journal of neurophysiology 1999-04, Vol.81 (4), p.1818-1826
• Main Authors: Brezden, B. L, Yeoman, M. S, Gardner, D. R, Benjamin, P. R
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Animals; Calcium - metabolism; Calcium Channels - metabolism; Down-Regulation - genetics; FMRFamide - genetics; FMRFamide - pharmacology; Gene Expression - physiology; Lymnaea; Membrane Potentials - drug effects; Membrane Potentials - physiology; Molecular Sequence Data; Myocardium - chemistry; Myocardium - cytology; Neuropeptides - genetics; Neuropeptides - metabolism; Patch-Clamp Techniques; Up-Regulation - genetics
• ISSN: 0022-3077; 1522-1598
• DOI: 10.1152/jn.1999.81.4.1818

  1 Ottawa-Carleton Institute of Biology, Carleton University, Ottawa, Ontario K1S 5B6, Canada; and   2 Sussex Centre for Neuroscience, School of Biological Sciences, University of Sussex, Falmer, Brighton, East Sussex BN1 9QG, United Kingdom Brezden, B. L., M. S. Yeoman, D. R. Gardner, and P. R. Benjamin. FMRFamide-activated Ca 2+ channels in Lymnaea heart cells are modulated by "SEEPLY," a neuropeptide encoded on the same gene. The cell-attached, patch-clamp technique was used to investigate the modulatory role of the neuropeptide SEQPDVDDYLRDVVLQSEEPLY ("SEEPLY") on FMRFamide-activated Ca 2+ channels in isolated Lymnaea heart ventricular cells. Both SEEPLY and FMRFamide are encoded on the same neuropeptide gene and are coexpressed in a pair of excitatory motor neurons that innervate the heart. FMRFamide applied alone was capable of significantly increasing the P (open) time of a Ca 2+ channel in isolated heart muscle cells. However, SEEPLY applied alone did not significantly alter the basal level of Ca 2+ channel activity in the same cells. Repeated applications of FMRFamide (15 s every min) resulted in a progressive reduction in the number of Ca 2+ channel openings and the overall P (open) time of the channel. The fifth successive 15-s application of FMRFamide failed to cause the Ca 2+ channels to open in the majority of cells tested. When FMRFamide and SEEPLY were repeatedly applied together (2-min applications every 4 min) the FMRFamide-activated Ca 2+ channels continued to respond after the fifth application of the two peptides. Indeed channel activity was seen to continue after repeated 2-min applications of FMRFamide and SEEPLY for as long as the patch lasted ( 60 min). As well as preventing the loss of response to FMRFamide, SEEPLY was also capable of both up- and down-regulating the response of the Ca 2+ channel to FMRFamide. The direction of the response depended on the P (open) time of the channel before the application of SEEPLY. When the P (open) time for the FMRFamide-activated channel was initially 0.004 ± 0.002 (means ± SE), subsequent perfusion with a mixture of FMRFamide and SEEPLY produced a statistically significant increase in Ca 2+ channel activity (13 cells). In two cells where no channel activity was observed in response to an initial application of FMRFamide, superfusing the heart cells with a mixture of FMRFamide and SEEPLY induced openings of the Ca 2+ channel. When the P (open) time of FMRFamide-induced Ca 2+ channel openings