Prostaglandin E1 receptor from mouse mastocytoma P-815 cells couples to 60 kDa GTP-binding protein

Contribution of phosphoinositide-dependent signalling to photomotility of Blepharisma ciliate

The effect of experimental procedures designed to modify an intracellular phosphoinositide signalling pathway, which may be instrumental in the photophobic response of the protozoan ciliate Blepharisma japonicum, has been investigated. To assess this issue, the latency time of the photophobic response and the cell photoresponsiveness have been assayed employing newly developed computerized videorecording and standard macro-photographic methods. Cell incubation with neomycin, heparin and Li+, drugs known to greatly impede phosphoinositide turnover, causes evident dose-dependent changes in cell photomotile behaviour. The strongest effect on photoresponses is exerted by neomycin, a potent inhibitor of polyphosphoinositide hydrolysis. The presence of micromolar concentrations of neomycin in the cell medium causes both prolongation of response latency and decrease of cell photoresponsiveness. Neomycin at higher concentrations (> 10 microM) abolishes the cell response to light at the highest applied intensity. A slightly lower inhibition of cell responsiveness to light stimulation and prolongation of response latency are observed in cells incubated in the presence of heparin, an inositol trisphosphate receptor antagonist. Lithium ions, widely known to deplete the intracellular phosphoinositide pathway intermediate, inositol trisphosphate, added to the cell medium at millimolar level, also cause a slowly developing inhibitory effect on cell photoresponses. Mastoparan, a specific G-protein activator, efficiently mimics the effect of light stimulation. In dark-adapted ciliates, it elicits ciliary reversal with the response latency typical for ciliary reversal during the photophobic response. Sustained treatment of Blepharisma cells with mastoparan also suppresses the photoresponsiveness, as in the case of cell adaptation to light during prolonged illumination. The mastoparan-induced responses can be eliminated by pretreatment of the cells with neomycin. Moreover, using antibodies raised against bovine transducin, a cross-reacting protein with an apparent molecular mass of about 55 kDa in the Blepharisma cortex fraction is detected on immunoblots. The obtained results indirectly suggest that the changes in internal inositol trisphosphate level, possibly elicited by G-protein-coupled phospholipase C, might play a role in the photophobic response of Blepharisma. However, further experiments are necessary to clarify the possible coupling between the G-protein and the putative phospholipase C.

Neuropeptide Y promotes GTP photo-incorporation into a 55 kDa protein

Incubation of bovine hippocampal membranes with [alpha-32P]GTP and exposure to ultraviolet light resulted in the labelling of seven species with apparent molecular masses of 200, 74, 55, 53, 50, 43 and 40 kDa. Labelling of the 55 kDa species was greatly enhanced in the presence of carboxyl terminal fragments [neuropeptide Y-(18-36)] of neuropeptide Y. Labelling occurred with [alpha-32P]GTP but not [alpha-32P]ATP. A group of putative direct G protein activating peptides including mastoparan, melittin, substance P and adrenocorticotropic hormone (ACTH)-(1-24), were also able to stimulate the labelling of this protein. Labelling of the 55 kDa protein could be demonstrated in bovine brain but not peripheral tissues. Western blot analysis using an antibody against the common alpha subunit of G proteins recognized a protein co-migrating with the 55 kDa GTP-binding protein. These findings demonstrate the existence of a previously uncharacterized neuronal protein, with an apparent molecular mass of 55 kDa, that binds GTP in response to neuropeptide Y and other peptides.

Biochemical and immunohistochemical demonstration of a tightly bound form of prostaglandin E2 in the rat brain

Basal levels of prostaglandin E2 in the rat brain were determined by radioimmunoassay to be 0.68-0.79 pmol/g brain. About one-third of the prostaglandin E2 (0.23-0.28 pmol/g) was resistant to extraction with ethanol, but could be recovered with a mixture of ethanol and 1 N HCl (9:1, v/v), indicating that a tightly bound form of prostaglandin E2 exists in the brain. The amount of the bound form of prostaglandin E2 was almost unchanged by pentylenetetrazole-induced convulsion or by transcardial perfusion with a formaldehyde solution, although these treatments resulted in 40- to 80-fold increases in prostaglandin E2 content extracted with ethanol at neutral pH. A polyclonal antibody against prostaglandin E2-albumin conjugates recognized the bound form of prostaglandin E2, giving a punctate appearance in many neuronal cell bodies in the brain. Although almost all of the neuronal perikarya were immunoreactive for prostaglandin E2, intense immunoreactivity was observed in the mitral cell layer of the olfactory bulb, layer V of the cerebral neocortex, anterodorsal and reticular nuclei of the thalamus, supraoptic, paraventricular, accessory neurosecretory and lateral mammaillary nuclei of the hypothalamus, mesencephalic trigeminal nucleus, nucleus of the trapezoid body and deep cerebellar nuclei. When the cerebral neocortical regions were observed electron microscopically, immunoreaction products were seen as fine granules which were clustered into small patches in the cytoplasm of neuronal cell bodies and proximal dendrites. No immunoreaction products were seen in glial cells or endothelial cells. These results suggest that prostaglandin E2 is involved in fundamental processes of neurons.