Immunocytochemical staining with antibodies against protein kinase C and its isozymes in the turtle retina

AMPA and Kainate Receptors in Turtle Retina: An Immunocytochemical Study

1. Glutamate is one of the main neurotransmitters in the retina. Its effects are mediated by a large number of ionotropic and metabotropic receptors.2. The distribution of ionotropic AMPA receptor subunits GluR1-4, kainate receptor subunits GluR5-7 and KA2, as well as delta receptors 1-2 was studied in turtle retina. Indirect immunofluorescence was used to localize the different receptor subunits viewed using light microscopy.3. Results show that all subunits, with exception of GluR1 and GluR5, are widely distributed in the turtle retina.4. They are mainly located in the both plexiform layers of the retina where punctate staining, a sign for synaptic localization, is observed.5. The vast majority of the subunits possess specific pattern of staining that allow to suppose that they are involved in different retinal circuits.6. It can be assumed that the GluR2/3 and GluR6/7 subunits are expressed on the dendrites of a subpopulation of bipolar cells that are immunopositive for alpha-isoform of protein kinase C (PKCalpha). The GluR2/3 and GluR6/7 subunits are most probably used by the same PKCalpha immunopositive bipolar cells in their synaptic contacts with the third-order retinal neurons, the amacrine and ganglion cells.

Immunocytochemical and electrophysiological characterization of GABA receptors in the frog and turtle retina

The expression of GABA receptors (GABARs) was studied in frog and turtle retinae. Using immunocytochemical methods, GABA(A)Rs and GABA(C)Rs were preferentially localized to the inner plexiform layer (IPL). Label in the IPL was punctate indicating a synaptic clustering of GABARs. Distinct, but weaker label was also present in the outer plexiform layer. GABA(A)R and GABA(C)R mediated effects were studied by recording electroretinograms (ERGs) and by the application of specific antagonists. Bicuculline, the GABA(A)R antagonist, produced a significant increase of the ERG. Picrotoxin, when co-applied with saturating doses of bicuculline, caused a further increase of the ERG due to blocking of GABA(C)Rs. The putative GABA(C)R antagonist Imidazole-4-acidic acid (I4AA) failed to antagonize GABA(C)R mediated inhibition and, in contrast, appeared rather as an agonist of GABARs.

Redistribution of protein kinase C isoforms in rat pancreatic acini during lactation and weaning

Freshly enzymatically isolated pancreatic acini from lactating and weaning Wistar rats were used to investigate the role of protein kinase C (PKC) isoforms during these physiologically relevant pancreatic secretory and growth processes. The combination of immunoblot and immunohistochemical analysis shows that the PKC isoforms alpha, delta, and epsilon are present in pancreatic acini from control, lactating and weaning rats. A vesicular distribution of PKC-alpha, -delta, and -epsilon was detected by immunohistochemical analysis in the pancreatic acini from all the experimental groups. PKC-delta showed the strongest PKC immunoreactivity (PKC-IR). In this vesicular distribution, PKC-IR was located at the apical region of the acinar cells. No differences were observed between control, lactating and weaning rats. However, the immunoblot analysis of pancreatic PKC isoforms during lactation and weaning showed a significant translocation of PKC-delta from the cytosol to the membrane fraction when compared with control animals. Translocation of PKC isoforms (alpha, delta and epsilon) in response to 12-O-tetradecanoyl phorbol 13-acetate (TPA) 1 microM (15 min, 37 degrees C) was comparable in pancreatic acini from control, lactating and weaning rats. In the control group, a significant translocation of all the isoforms (alpha, delta and epsilon) from the cytosol to the membrane was observed. The PKC isoform most translocated by TPA was PKC-delta. In contrast, no statistically significant increase in PKC-delta translocation was detected in pancreatic acini isolated from lactating or weaning rats. These results suggest that the PKC isoforms are already translocated to the surface of the acinar cells from lactating or weaning rats. In addition, they suggest that isoform specific spatial PKC distribution and translocation occur in association with the growth response previously described in the rat exocrine pancreas during lactation and weaning.

Up-regulation of protein kinase C in regenerating optic nerve fibers of goldfish: immunohistochemistry and kinase activity assay

Protein kinase C (PKC) activation has been associated with synaptic plasticity in many projections, and manipulating PKC in the retinotectal projection strongly affects the activity-driven sharpening of the retinotopic map. This study examined levels of PKC in the regenerating retinotectal projection via immunostaining and assay of activity. A polyclonal antibody to the conserved C2 (Ca2+ binding) domain of classical PKC isozymes (anti-panPKC) recognized a single band at 79-80 kD on Western blots of goldfish brain. It stained one class of retinal bipolar cells and the ganglion cells in normal retina, as shown previously. Strong staining was not present in the optic fiber layer of retina or in optic nerve, optic tract, or terminal zone in tectum, with the exception of a single fascicle of optic nerve fibers that by their location and by L1 (E587) staining were identified as those arising from newly added ganglion cells at the retinal margin. Normal tectal sections showed dark staining of a subclass of type XIV neuron with somas at the top of the periventricular layer and an apical dendrite ascending to stratum opticum. In regenerating retina, swollen ganglion cells stained darkly and stained axons were seen in the optic fiber layer. In regenerating optic nerve (2-11 weeks postcrush), all fascicles of optic fibers stained darkly for both PKC and L1(E587). At 5 weeks postcrush, PKC staining could also be seen in the medial and lateral optic tracts and stratum opticum at the front half of the tectum and very lightly over the terminal zones. PKC activity was measured in homogenized tissues dissected from a series of fish with unilateral nerve crush from 1 to 5 weeks previously. Activity levels stimulated by phorbols and Ca2+ were measured by phosphorylation of a specific peptide and referred to levels measured in the opposite control side. Regeneration did not increase overall PKC activity in retina or tectum, but in optic nerve there was an 80% rise after the first week. The increased activity verifies that the increased staining in nerve represented an up-regulation of functional PKC during nerve regeneration.

Protein kinase C activity and light sensitivity of single amphibian rods

Biochemical experiments by others have indicated that protein kinase C activity is present in the rod outer segment, with potential or demonstrated targets including rhodopsin, transducin, cGMP-phosphodiesterase (PDE), guanylate cyclase, and arrestin, all of which are components of the phototransduction cascade. In particular, PKC phosphorylations of rhodopsin and the inhibitory subunit of PDE (PDE ) have been studied in some detail, and suggested to have roles in downregulating the sensitivity of rod photoreceptors to light during illumination. We have examined this question under physiological conditions by recording from a single, dissociated salamander rod with a suction pipette while exposing its outer segment to the PKC activators phorbol-12-myristate,13-acetate (PMA) or phorbol-12,13-dibutyrate (PDBu), or to the PKC-inhibitor GF109203X. No significant effect of any of these agents on rod sensitivity was detected, whether in the absence or presence of a background light, or after a low bleach. These results suggest that PKC probably does not produce any acute downregulation of rod sensitivity as a mechanism of light adaptation, at least for isolated amphibian rods.

Differential staining of neurons in the human retina with antibodies to protein kinase C isozymes

Monoclonal antibodies to the three isozymes of protein kinase C (PKC) (alpha, beta, and gamma) were applied to postmortem human retina. Immunostaining was done on wholemount, or cryostat-sectioned retina, and visualized after ABC/DAB procedures by light (LM) and electron (EM) microscopy. The PCK-alpha antibody stained rod bipolar cells throughout the retina. EM analysis confirmed they were PKC-alpha-immunoreactive (IR) on their characteristic dendritic and axonal synaptology. Putative blue cone bipolar cells with wide-field axon terminals, stratifying in s5 of the inner plexiform layer (IPL), were also PKC-alpha-IR, and EM showed them to engage in narrow-cleft ribbon junctions in blue cone pedicles. The PKC-beta antibody stained cone bipolar cells, many amacrine cells, and most ganglion cells. Cone bipolar cells were stained all the way into the foveal center: both midget and diffuse varieties were included. The IPL was densely PKC-IR and individual neurons could not be identified on stratification patterns. EM of the outer plexiform layer (OPL) revealed that both flat and invaginating cone bipolar types were IR and that IR axon terminals were presynaptic in all strata of the IPL. The occurrence of PKC-beta-IR bipolar axons in stratum 2 of the IPL suggests that OFF-center as well as ON-center types were included. The PKC-gamma antibody gave inferior staining compared with results from the other two antibodies; however, two varieties of wide-field monostratified amacrine cell and a large-bodied ganglion cell type were discernible. PKC in one form or another appears to be a second messenger used in neurotransmission by both rod and cone systems and ON- and OFF-center systems in the human retina.