Calcium homeostasis in photoreceptor cells of Drosophila mutants inaC and trp studied with the pupil mechanism

The light-driven pupil mechanism, consisting of an assembly of mobile pigment granules inside the photoreceptor cells, has been investigated by in vivo reflection microspectrophotometry in wild type (WT) Drosophila and in the photoreceptor mutants inaC and trp. The pupillary response of a dark-adapted WT eye to a step in light is a monophasic reflectance increase reaching a plateau after ca. 15-s light adaptation. This reflectance change is due to photoreceptor pigment granules that accumulate near the tips of the rhabdomeres under light adaptation and that are withdrawn towards the periphery in the dark (Franceschini & Kirschfeld, 1976). The step response of the pupil mechanism of inaC is triphasic. Strikingly, the reflectance level at light onset is distinctly higher than that in WT, due to a partly aggregated state of the photoreceptor pigment granules near the rhabdomere tips that persists in the dark-adapted state, in line with direct calcium measurements of Peretz et al. (1994b). The step response of the pupil mechanism of inaC is slightly elevated compared to that of WT. The step response in trp is a transient, biphasic reflectance change, approximating a log normal function. This function is also a good approximation of the pulse response in WT and inaC. The intensity range of pupillary sensitivity is about 4 log unit. The range of inaC compared to that of WT is slightly (approximate to 0.5 log unit) shifted towards lower intensities, but that in trp is strongly shifted to higher intensities (approximate to 2.5 log unit). The results can be interpreted with the present knowledge of the primary steps in fly phototransduction and the hypothesis that the local intracellular calcium concentration determines the position of the pigment granules, and hence are in line with the notion that the pupil can be used as a qualitative Ca2+ probe

Differential effects of ninaC proteins (p132 and p174) on light-activated currents and pupil mechanism in Drosophila photoreceptors

The Drosophila ninaC locus encodes two retinal specific proteins (p132 and p174) both consisting of a protein kinase joined to a myosin head domain and a C terminal with a calmodulin-binding domain. The role of p132 and p174 was studied via whole-cell recording and through measurements of the pupil mechanism, i.e. the pigment migration in the photoreceptor cells, in the ninaC mutants, P[ninaC(Delta 132)] (p132 absent), P[ninaC(Delta 174)] (p174 absent), and ninaC(P235) (null mutant). Voltage-clamped flash responses in P[ninaC(Delta 174)] and ninaC(P235) showed delayed response termination. In response to steady light, plateau responses in both P[ninaC(Delta 174)] and ninaC(P235) were also large. In both cases the defect was significantly more severe in ninaC(P235). Responses in P[ninaC(Delta 132)] were apparently normal. P[ninaC(Delta 174)] and ninaC(P235) were also characterized by spontaneous quantum bump-like activity in the dark and by larger and longer light-induced quantum bumps. The turn-off of the pupil mechanism in P[ninaC(Delta 174)] and ninaC(P235) was also defective, although in this case the rate of return to baseline in both mutants was more or less the same. In all ninaC mutants, the amplitudes of the pupillary pigment migration were distinctly smaller than that in the wild type. The reduction of the amplitude was largest in P[ninaC(Delta 174)]. The light sensitivity of the pupil mechanism of P[ninaC(Delta 174)] compared to that of wild type was reduced by 1.3 log units. Remarkably, the light sensitivity of P[ninaC(Delta 132)] and ninaC(P235) was ca. 0.5 log units higher than that of the wild type. The results suggest that the p174 protein is required for normal termination of the transduction cascade. The diverse phenotypes observed may suggest multiple roles for calmodulin distribution for controlling response termination and regulating pigment migration in Drosophila photoreceptors

Membrane with incorporated hydrophobic ligand for hydrophobic interaction with proteins: application to lipase adsorption

Conference on Polymers in the 3rd Millennium -- SEP 02-06, 2001 -- MONTPELLIER, FRANCEWOS: 000179103200020In this study, phenylalanine as a hydrophobic ligand was covalently attached on a comonomer, methacryloyl chloride. Then, poly(2-hydroxyethyl methacrylate-co-methacrylamido-phenylalanine), poly(HEMA/MAPA), membranes were prepared by UV-initiated photopolymerization of 2-hydroxyethyl methacrylate and methacrylamido-phenylalanine. The lipase adsorption of these poly(HEMA/MAPA) membranes was determined by changing the hydrophobic ligand density, pH, temperature and concentration of lipase in the adsorption medium. The lipase adsorption capacity of the membranes increased as the ligand density on the membrane surface increased. The nonspecific adsorption of lipase on the poly(2-hydroxyethyl methacrylate) membranes was negligible (12 mug cm(-2) of membrane). The adsorption phenomena appeared to follow a typical Langmuir isotherm. The maximum adsorption capacity (Q(m)) of the poly(HEMA/MAPA-5) membrane for lipase was 215 mug cm(-2) of membrane. The equilibrium constant (k(d)) value was 1.43mg ml(-1). The lipase could repeatedly be adsorbed and desorbed on the affinity membrane without any significant loss in the adsorption capacity of the membrane. (C) 2002 Society of Chemical Industry.Soc Chem Ind & Polymer Int, IEEE Dielectr & Electr Insulat Soc, IAE, SISM, WILEY, IEEE, DEI

Visualization of competitive market structure by means of choice data

Three-mode PCA, Elasticities, Joint plots, Market structure analysis,