Ca²⁺ influx via trp channels is required to maintain phosphatidylinositol 4,5, bisphosphate (PIP₂) levels in photoreceptors.

The trp-inaD protein-protein interaction is required for maintaining transduction complexes in the rhabdomeres.

The trp and trpl channels are specific targets of metabolic stress; anoxia opens trp and trpl channels in the dark. Mitochondrial uncouplers and depletion of ATP activate the trp and trpl channels in the dark in situ.

trp dependent channels have a small unitary conductance. Many channels can be gated coordinately.

The fact that the ability of non-inaD bound trp to contribute to photoreceptor responses depends on the presence of trpl suggests that there may be interactions between trpl and the non-inaD-bound trp protein.

trp mutants are normal in olfactory response but defective in olfactory adaptation.

trp has a role in olfactory system development.

A PDZ domain is required in vivo for anchoring an ion channel to its normal subcellular site: inaD is required for spatially localising trp to a large signalling complex.

The biophysical properties of trpl channels expressed in a stably transfected cell line are compared to those of trp. Results show that, for a wide range of properties, the native and expressed channels are functionally equivalent lending strong support to the proposal that channels encoded by trpl can completely account for the component of the light-sensitive conductance remaining in the trp mutant.

Wild-type light activated conductance is composed of two separate channels, with the properties of trp- and trpl-encoded channels as determined in the respective mutants.

Coexpression of trp and trpl leads to a store-operated, outwardly rectifying current distinct from that owing to either trp or trpl alone. trp and trpl proteins interact directly, indicating the trp-trpl-dependent current is mediated by heteromultimeric association between the two subunits.

Reflectance measurements performed on inaC and trp photoreceptor mutants confirm that the pupil can serve as a useful tool in fly phototransduction research.

trpl activity is masked by functional trp channels and together trp and trpl are essential components of the light-activated conductance. trp and trpl need not form heteromeric channels because trpl mutants only contain trp protein and trp mutants only have trpl protein. Since trp and trpl mutants respond to light activation then each channel on its own must be capable of sensing the intracellular messenger that gates the light activated conductance. Activation of one does not require prior activation of the other.

Antibodies to the inaD protein co-precipitate trp gene product. The interaction has been mapped to the 19 amino acid C-terminus of trp and the PDZ domain of inaD. inaD functions as a regulatory subunit of the trp Ca²⁺ channel.

Analysis of trp-trpl fusion proteins suggests that the carboxy terminal domain of trpl plays an important role in determining constitutive activity of the protein, and the carboxy terminal domain of trp contains structural features necessary for activation by thapsigargin.

trp may function as a capacitative calcium entry channel.

The subcellular localisation of trp protein has been determined.

Light induces a rapid increase in internal calcium concentration in photoreceptors. Mutations in trp reduce the inward flux of calcium in the photoreceptors.

The calmodulin-binding and ankyrin-repeats have been investigated in vitro using fusion proteins.

Drosophila photoreceptors have two light activated photoreceptors, one of which is highly selective for Ca²⁺ and trp-dependent. Double mutants of trp and inaC were compared with the single mutants in whole cell recordings in dissociated ommatidia. Results indicate that both trp-dependent and trp-independent channel classes require inaC PKC gene product for their normal regulation.

Expression analysis results suggest that the trp protein is a novel photoreceptor membrane associated protein. Proper function of the trp gene product during pupal development is important for normal visual transduction in the adult.

Developmental expression pattern of the cDNA clone is examined.

Identified as a cDNA clone that is expressed at a low frequency in the body but abundantly in the head of the adult.

The same kinds of results from applying fluoride ions or the GPT analogue to the trp mutant in Drosophila (see 'phenotype') were observed in experiments on the nss mutant in the blowfly Lucilia.

Mutation believed to affect an intermediate step in phototransduction, the wild-type gene apparently encoding a protein involved in an intermediate step between photoreception and opening of the light-sensitive ion channels (Minke, 1977; Minke, 1982; Minke and Armon, 1980; Montell and Rubin, 1989; Suss et al., 1989). Although the mutants behave normally in dim light, they behave as though blind in bright light and there is an abnormally slow dark recovery (Cosens and Manning, 1969; Cosens, 1971). The light-evoked response of the photoreceptors, as shown in the ERG, decays to baseline during an intense, prolonged stimulus, but not during a dim or brief stimulus (Cosens and Manning, 1969; Minke, Wu and Pak, 1975); each quantum bump, however, seems intrinsically normal in shape and amplitude (Suss et al., 1989); fluoride ions, which lead to excitation and adaptation of wild-type photoreceptors in the dark when superfused onto an eye slice, did neither to mutant cells. A hydrolysis-resistant analogue of GTP, which excites wild-type photoreceptors and results in noisy depolarizations, reduced the mutant's light response. The visual pigment in R1-6 photoreceptors is normal in young trp flies, but its concentration decreases with age (Minke, 1982). The rhabdomeres degenerate with age and there is accumulation of glycogen granules (Cosens and Perry, 1972). Ultimately, photoreceptor cell bodies also degenerate (Isono, unpublished). Raising the mutant flies in complete darkness prevents the degenerative changes from appearing but has no effect on the electrophysiological phenotype (Isono and Pak, unpublished). Initially, the light-evoked migration of pigment granules occurs in a normal manner (i.e., toward the rhabdomeres) in trp mutants, but the granules move away after only five seconds of sustained light (Lo and Pak, 1981). The trp mutation (unlike norpA) does not block degeneration caused by rdgB (Chen and Stark, 1983); in a rdgB;trp genetic background, R1-6 photoreceptors are eliminated and the R7,8 photoreceptors that remain show the trp phenotype. trp is expressed in the photoreceptors of the ocelli as well as in those of the compound eyes (Hu, Reichert and Stark, 1978; Montell, Jones, Hafen and Rubin, 1985). trp mutants seem to exhibit normal visually-mediated learning under the high light-intensity conditions that largely eliminate photoreceptor potentials (Reichert and Bicker, 1979).