TRPgamma channels are inhibited by cAMP and contribute to pacemaking in neurosecretory insect neurons.
From a neuronal cDNA library of the cockroach Periplaneta americana we isolated a 3585-bp cDNA sequence encoding Periplaneta transient receptor potential gamma (pTRPgamma), a protein of 1194 amino acids showing 65% identity to the orthologous Drosophila channel protein dTRPgamma. Heterologous expression of pTRPgamma in HEK293 cells produced a constitutively active, non-selective cation channel with a Ca2+:Na+ permeability ratio of 2. In contrast to dTRPgamma-mediated currents, pTRPgamma currents were partially inhibited by 8-bromo-cAMP, and this effect was not mediated by protein kinase A (PKA) activation. pTRPgammab, a truncated pTRPgamma splice variant missing most of the C terminus, was insensitive to 8-bromo-cAMP. Thus, the critical cAMP-binding site seems to be located in the C-terminal part of pTRPgamma, although there is no common cAMP-binding consensus sequence. While dTRPgamma is only expressed in the photoreceptors, pTRPgamma is expressed throughout the nervous system. In particular it is expressed in dorsal unpaired median (DUM) neurons. In these octopamine-releasing, neurosecretory cells a Ca2+ background current contributing to pacemaker activity was found to be up-regulated by the reduction of cAMP level. In addition, the Ca2+ background current was inhibited by LOE-908, 2-APB, and La3+, which similarly affected the pTRPgamma current. We thus propose that the pTRPgamma protein is involved in forming the channel passing the Ca2+ pakemaking background current in DUM neurons.
Wicher
Dieter
D
Department of Neurohormones, Saxon Academy of Sciences, 07743 Jena, Germany. dwicher@ice.mpg.de
Agricola
Hans-Jürgen
HJ
Schönherr
Roland
R
Heinemann
Stefan H
SH
Derst
Christian
C
D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000378:metabolism; D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D000242:Cyclic AMP / Q000378:metabolism*; D018076:DNA, Complementary / Q000378:metabolism; D015536:Down-Regulation; D004330:Drosophila; D029721:Drosophila Proteins / Q000378:metabolism / Q000502:physiology*; D004594:Electrophysiology; D005822:Genetic Vectors; D006801:Humans; D007150:Immunohistochemistry; D007313:Insecta; D007473:Ion Channels / Q000378:metabolism / Q000502:physiology*; D007477:Ions / Q000737:chemistry; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D009420:Nervous System / Q000378:metabolism; D009474:Neurons / Q000378:metabolism*; D010455:Peptides / Q000737:chemistry; D010526:Periplaneta / Q000378:metabolism; D017956:Photoreceptor Cells, Invertebrate; D017434:Protein Structure, Tertiary; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid; D012964:Sodium / Q000737:chemistry; D050051:Transient Receptor Potential Channels
D018076:DNA, Complementary; D029721:Drosophila Proteins; D007473:Ion Channels; D007477:Ions; D010455:Peptides; C411581:TRPgamma protein, Drosophila; D050051:Transient Receptor Potential Channels; D015124:8-Bromo Cyclic Adenosine Monophosphate; D012964:Sodium; D000242:Cyclic AMP; D002118:Calcium