DIFFERENTIAL DISTRIBUTION OF TRP CA2-BRAIN( CHANNEL ISOFORMS IN MOUSE)

MAMMALIAN homologues of the Drosophila TRP proteins, which are essenti al for light-activated, phosphatidyl-inositide (PI)-dependent Ca2+ con ductance in Drosophila photoreceptors, were molecularly identified, to investigate receptor-activated Ca2+ influx in the mammalian nervous s ystem. Two cloned mouse TRP homologues, TRP3 and TRP4, structurally re lated to the voltage-dependent Na+ channel, were expressed predominant ly in the brain, where a sharp contrast in the distribution of the RNA transcripts for TRP isoforms was demonstrated by in situ hybridizatio n analysis. TRP3 mRNA was concentrated in cerebellar Purkinje cells an d sparsely localized in the cerebellar granule layer, pontine nuclei, and thalamus, whereas TRP4 mRNA was abundantly expressed in hippocampa l CA1 pyramidal neurons, dentate gyrus granule cells, and cerebral cor tical neurons, and in the septal nuclei and the mitral layer of olfact ory bulb. The distinct spacial patterns of TRP isoforms implicate that neurons are highly heterogeneous in receptor-activated Ca2+ influx re sponsible for the second phase of PI-mediated rise in intracellular Ca 2+.