Protein kinase C (alpha and beta) immunoreactivity in rabbit and rat retina: effect of phorbol esters and transmitter agonists on immunoreactivity and the translocation of the enzyme from cytosolic to membrane compartments

The Effects of Aging on Rod Bipolar Cell Ribbon Synapses

The global health concern posed by age-related visual impairment highlights the need for further research focused on the visual changes that occur during the process of aging. To date, multiple sensory alterations related to aging have been identified, including morphological and functional changes in inner hair cochlear cells, photoreceptors, and retinal ganglion cells. While some age-related morphological changes are known to occur in rod bipolar cells in the retina, their effects on these cells and on their connection to other cells via ribbon synapses remain elusive. To investigate the effects of aging on rod bipolar cells and their ribbon synapses, we compared synaptic calcium currents, calcium dynamics, and exocytosis in zebrafish (Danio rerio) that were middle-aged (MA,18 months) or old-aged (OA, 36 months). The bipolar cell terminal in OA zebrafish exhibited a two-fold reduction in number of synaptic ribbons, an increased ribbon length, and a decrease in local Ca2+ signals at the tested ribbon location, with little change in the overall magnitude of the calcium current or exocytosis in response to brief pulses. Staining of the synaptic ribbons with antibodies specific for PKCa revealed shortening of the inner nuclear and plexiform layers (INL and IPL). These findings shed light on age-related changes in the retina that are related to synaptic ribbons and calcium signals.

Changes in the Inner Retinal Cells after Intense and Constant Light Exposure in Sprague-Dawley Rats

Light insult causes photoreceptor death. Few studies reported that continuous exposure to light affects horizontal, Müller and ganglion cells. We aimed to see the effect of constant light exposure on bipolar and amacrine cells. Adult Sprague-Dawley rats were exposed to 300 or 3000 lux for 7 days in 12-h light: 12-h dark cycles (12L:12D). The latter group was then exposed to 24L:0D for 48 h to induce significant damage. The same animals were reverted to 300 lux and reared for 15 days in 12L:12D cycles. They were sacrificed on different days to find the degree of retinal recovery, if any, from light injury. Besides photoreceptor death, continuous light for 48 h resulted in downregulation of parvalbumin in amacrine cells and recoverin in cone bipolar cells (CBC). Rod bipolar cells (RBC) maintained an unaltered pattern of PKC-α expression. Upon reversal, there were increased expressions of parvalbumin in amacrine cells and recoverin in CBC, while RBC showed an increasing trend of PKC-α expression. The data show that damage in bipolar and amacrine cells after exposure to intense, continuous light can be ameliorated upon reversal to normal LD cycles to which the animals were initially acclimated to.

Differential expression of PKCα and -β in the zebrafish retina

The retina is a complex neural circuit, which processes and transmits visual information from light perceiving photoreceptors to projecting retinal ganglion cells. Much of the computational power of the retina rests on signal integrating interneurons, such as bipolar cells. Commercially available antibodies against bovine and human conventional protein kinase C (PKC) α and -β are frequently used as markers for retinal ON-bipolar cells in different species, despite the fact that it is not known which bipolar cell subtype(s) they actually label. In zebrafish (Danio rerio) five prkc genes (coding for PKC proteins) have been identified. Their expression has not been systematically determined. While prkcg is not expressed in retinal tissue, the other four prkc (prkcaa, prkcab, prkcba, prkcbb) transcripts were found in different parts of the inner nuclear layer and some as well in the retinal ganglion cell layer. Immunohistochemical analysis in adult zebrafish retina using fluorescent in situ hybridization and PKC antibodies showed an overlapping immunolabeling of ON-bipolar cells that are most likely of the BON s6 and BON s6L or RRod type. However, comparison of transcript expression with immunolabeling, implies that these antibodies are not specific for one single zebrafish conventional PKC, but rather detect a combination of PKC -α and -β variants.

Immunohistochemical localization of protein kinase C (PKC) beta I in the pig retina during postnatal development

In order to investigate the expression of protein kinase C (PKC) beta I in the retinas of pigs during postnatal development, we analyzed retinas sampled from 3-day-old and 6-month-old pigs by Western blotting and immunohistochemistry. Western blot analysis detected the expression of PKC beta I in the retinas of 3-day-old piglets and it was increased significantly in the retinas of 6-month-old adult pigs. Immunohistochemical staining showed PKC beta I in the retinas of both groups. Immunohistochemistry of 3-day-old retinas revealed weak PKC beta I reactivity in the ganglion cell layer, inner plexiform layer, inner nuclear cell layer, outer plexiform layer and rod and cone cell layer. In the 6-month-old pig retina, the cellular localization of PKC beta I immunostaining was similar to that of the 3-day-old retina, where PKC beta I was localized in some glial fibrillary acidic protein-positive cells, glutamine synthetase-positive cells, parvalbumin-positive cells, and PKC alpha-positive cells in the retina. This is the first study to show the expression and cellular localization of PKC beta I in the retina of pigs with development, and these results suggest that PKC beta I, in accordance with PKC alpha, plays important roles in signal transduction pathways in the pig retina with development.

Probing potassium channel function in vivo by intracellular delivery of antibodies in a rat model of retinal neurodegeneration

Inward rectifying potassium (Kir) channels participate in regulating potassium concentration (K(+)) in the central nervous system (CNS), including in the retina. We explored the contribution of Kir channels to retinal function by delivering Kir antibodies (Kir-Abs) into the rat eye in vivo to interrupt channel activity. Kir-Abs were coupled to a peptide carrier to reach intracellular epitopes. Functional effects were evaluated by recording the scotopic threshold response (STR) and photopic negative response (PhNR) of the electroretinogram (ERG) noninvasively with an electrode on the cornea to determine activity of the rod and cone pathways, respectively. Intravitreal delivery of Kir2.1-Ab coupled to the peptide carrier diminished these ERG responses equivalent to dimming the stimulus 10- to 100-fold. Immunohistochemistry (IHC) showed Kir2.1 immunostaining of retinal bipolar cells (BCs) matching the labeling pattern obtained with conventional IHC of applying Kir2.1-Ab to fixed retinal sections postmortem. Whole-cell voltage-clamp BC recordings in rat acute retinal slices showed suppression of barium-sensitive Kir2.1 currents upon inclusion of Kir2.1-Ab in the patch pipette. The in vivo functional and structural results implicate a contribution of Kir2.1 channel activity in these electronegative ERG potentials. Studies with Kir4.1-Ab administered in vivo also suppressed the ERG components and showed immunostaining of Müller cells. The strategy of administering Kir antibodies in vivo, coupled to a peptide carrier to facilitate intracellular delivery, identifies roles for Kir2.1 and Kir4.1 in ERG components arising in the proximal retina and suggests this approach could be of further value in research.

PKC{alpha} is essential for the proper activation and termination of rod bipolar cell response

PURPOSE

Protein kinase (PKC)-α is abundant in retinal bipolar cells. This study was performed to explore its role in visual processing.

METHODS

PKCα-knockout (Prkca(-/-)) mice and control animals were examined by using electroretinography (ERG), light microscopy, and immunocytochemistry.

RESULTS

The Prkca(-/-) mice showed no signs of retinal degeneration up to 12 months of age, but ERG measurements indicated a decelerated increase in the ascending limb of the scotopic (rod-sensitive) b-wave as well as a delayed return to baseline. These results suggest that PKCα is an important modulator that affects bipolar cell signal transduction and termination. Confocal microscopy of retinal sections showed that PKCα co-localized with calbindin, which indicates a PKCα localization in close proximity to the horizontal cell terminals. In addition, the implicit time of the ERG c-wave originating from the retinal pigment epithelium (RPE) and the recovery of photoreceptors from bleaching conditions were substantially faster in the knockout mice than in the wild-type control animals.

CONCLUSIONS

These results suggest that PKCα is a modulator of rod-bipolar cell function by accelerating glutamate-driven signal transduction and termination. This modulation is of importance in the switch between scotopic and photopic vision. Furthermore, PKCα seems to play a role in RPE function.

Retinal development and function in a 'blind' mole

Animals adapted to dark ecotopes may experience selective pressure for retinal reduction. No previous studies have explicitly addressed the molecular basis of retinal development in any fossorial mammal. We studied retinal development and function in the Iberian mole Talpa occidentalis, which was presumed to be blind because of its permanently closed eyes. Prenatal retina development was relatively normal, with specification of all cell types and evidence of dorsoventral regionalization. Severe developmental defects occurred after birth, subsequent to lens abnormalities. 'Blind' Iberian moles had rods, cones and rod nuclear ultrastructure typical of diurnal mammals. DiI staining revealed only contralateral projections through the optic chiasm. Y-maze experiments demonstrated that moles retain a photoavoidance response. Over-representation of melanopsin-positive retinal ganglion cells that mediate photoperiodicity was observed. Hence, molecular pathways of eye development in Iberian moles retain the adaptive function of rod/cone primary vision and photoperiodicity, with no evidence that moles are likely to completely lose their eyes on an evolutionary time scale.

Rod bipolar cells in the retina of the capuchin monkey (Cebus apella): Characterization and distribution

Rod bipolar cells in Cebus apella monkey retina were identified by an antibody against the alpha isoform of protein kinase C (PKCα), which has been shown to selectively identify rod bipolars in two other primates and various mammals. Vertical sections were used to confirm the identity of these cells by their characteristic morphology of dendrites and axons. Their topographic distribution was assessed in horizontal sections; counts taken along the dorsal, ventral, nasal, and temporal quadrants. The density of rod bipolar cells increased from 500 to 2900 cells/mm2 at 1 mm from the fovea to reach a peak of 10,000–12,000 cells/mm2 at 4 mm, approximately 5 deg of eccentricity, and then gradually decreased toward retinal periphery to values of 5000 cells/mm2 or less. Rod to rod bipolar density ratio remained between 10 and 20 across most of the retinal extension. The number of rod bipolar cells per retina was 6,360,000 ± 387,433 (mean ± s.d., n = 6). The anti-PKCα antibody has shown to be a good marker of rod bipolar cells of Cebus, and the cell distribution is similar to that described for other primates. In spite of the difference in the central retina, the density variation of rod bipolar cells in the Cebus and Macaca as well as the convergence from rod to rod bipolar cells are generally similar, suggesting that both retinae stabilize similar sensitivity (as measured by rod density) and convergence.

Cancer-Induced, Immune-Mediated Ocular Degenerations

The means whereby vision can be lost from a disease located distant from the eye include autoimmunity, with sensitization resulting from extraocular stimuli, a process illustrated here by the immunologic confusion caused by cancers. The uncontrolled proliferation of malignancies commonly involves the expression of components of the central nervous system, but a damaging loss of tolerance is rare. When autoimmunity does develop, organ-specific antigens are more often involved than the more generalized and widely disseminated common neuronal components. A focus upon a single antigen is typical of the immune-mediated paraneoplasia, a collection of syndromes identified by unusual antibody reactions. This review provides an outline of the immunologic trail that led to the recognition of autoimmunity in paraneoplastic ocular degenerations, how specific antibody reactions aid in diagnosis, and the possibility of including antibodies in modes for sight-saving intervention. 'Those who do not know history are destined to repeat it'.

Immunohistochemical localization of protein kinase C-alpha in the retina of pigs during postnatal development

The cellular localization and protein expression level of protein kinase C (PKC)-alpha was examined in pig retina at different ages. Western blot analysis detected PKC-alpha in the retinas of 3-day-old piglets and indicated significantly increased expression in 6-month-old young adult and 2-year-old adult pigs. Immunohistochemistry of 3-day-old retinas revealed intense PKC-alpha reactivity in the inner plexiform and inner nuclear cell layers, weak reactivity in the ganglion cell layer, and few positive cells in the outer nuclear cell layer. The cellular localization of PKC-alpha in the adult retina was similar, with staining more intense than that in neonates. PKC-alpha was co-localized in some glial fibrillary acidic protein-positive cells and glutamine synthetase-positive cells in the retina. This study demonstrates that the protein level of retinal PKC-alpha is increased with maturation and suggests that PKC-alpha plays a role in signal transduction pathways for postnatal development in porcine retina.

Protein kinase C subtypes and retinal ischemic preconditioning

The purpose of our study was to determine the specific subtypes of protein kinase C involved in the neuroprotection afforded by retinal ischemic preconditioning (IPC), their relationship to the opening of mitochondrial KATP (mKATP) channels, and their role in apoptosis after preconditioning and ischemia. Rats were subjected to retinal ischemia after IPC, or retinas were rendered ischemic after pharmacological opening of mKATP channels. Using immunohistochemistry and image analysis, we determined cellular localization of PKC subtypes. We blocked PKC-delta and -epsilon to study the effect on protection with IPC or with IPC-mimicking by the opening of mKATP channels. PKC subtypes were inhibited pharmacologically or with interfering RNA. Electroretinography assessed functional recovery after ischemia. IPC was effectively mimicked by injection of diazoxide to open the mKATP channel. IPC and/or its mimicking were attenuated by the PKC-delta inhibitor rottlerin and by interfering RNA targeting PKC-delta or -epsilon. Using TUNEL staining and Western blotting for caspase-3 and fodrin breakdown we assessed apoptosis. The injection of interfering RNA to PKC-delta and -epsilon before preconditioning significantly enhanced TUNEL staining as well as the cleavage of caspase-3 and fodrin after ischemia. In summary, our experiments have shown that both PKC-delta and -epsilon subtypes are involved in the cellular signaling that results in neuroprotection from IPC and that both are downstream of the opening of mKATP channels.

Retinal function and PKC alpha expression after focal laser photocoagulation

PURPOSE

To examine the effects of focal laser photocoagulation on general and local retinal function and to relate electrophysiological findings with changes in protein kinase C (PKC) alpha expression.

METHODS

Twelve rabbits were treated with 70 spots of laser photocoagulation in the central cone-rich retina. The operated eyes were investigated with electroretinography (full-field ERG and multifocal electroretinography, mfERG) preoperatively and at 1, 3, and 5 weeks after surgery. The expression of PKC alpha was examined at all three time points using immunohistochemistry, and PKC alpha mRNA levels were quantified using real-time polymerase chain reaction (PCR). Immunohistochemistry for glial fibrillary acidic protein (GFAP) and hematoxylin and eosin staining was employed to monitor the extent and dynamics of the morphological response.

RESULTS

The full-field ERG revealed a significant increase in b-wave amplitudes derived from the isolated rod response (blue light) at all three time points after surgery (p < 0.05). Supernormal b-wave amplitudes were also found for the combined rod-cone response at 3 weeks (white light), and for the isolated cone response (light-adapted 30-Hz flicker) at 5 weeks after treatment. In the mfERG, amplitudes derived from the central retina did not change postoperatively, while the implicit time was significantly increased at all time points. Immunohistochemistry for PKC alpha revealed a reduced expression of the enzyme in rod bipolar cells 1 and 3 weeks after laser treatment compared with untreated controls. Five weeks postoperatively, no PKC alpha labeling in rod bipolar cells was found in any part of the retina. Real-time PCR 1 and 3 weeks after treatment displayed a decreased level of PKC alpha mRNA compared to the controls. Immunolabeled tissue sections from laser-treated eyes displayed GFAP expression in Müller cells in the treated as well as untreated retina 1 week postoperatively. At 3 and 5 weeks, GFAP labeling was less pronounced and was concentrated around the laser-treated spots.

CONCLUSIONS

Focal laser treatment in the rabbit eye induces local and wide-spread alterations in both rod- and cone-mediated retinal function in the form of supernormal b-wave amplitudes in the full-field ERG and increased latency in the mfERG. The electrophysiological abnormalities are accompanied by a progressive down-regulation of the PKC alpha isoenzyme in rod bipolar cells, reaching far beyond the treated area. PKC alpha is down-regulated directly by impaired protein synthesis, and also possibly indirectly by protein consumption related to GFAP up-regulation. The results indicate that focal laser photocoagulation interferes with PKC-alpha-mediated inhibitory regulation of inner retinal signal transmission.

Distribution of phosphorylated protein kinase C alpha in goldfish retinal bipolar synaptic terminals: control by state of adaptation and pharmacological treatment

Protein kinase C (PKC) is a signalling enzyme critically involved in many aspects of synaptic plasticity. In cyprinid retinae, the PKC alpha isoform is localized in a subpopulation of depolarizing bipolar cells that show adaptation-related morphological changes of their axon terminals. We have studied the subcellular localization of phosphorylated PKC alpha (pPKC alpha) in retinae under various conditions by immunohistochemistry with a phosphospecific antibody. In dark-adapted retinae, pPKC alpha immunoreactivity is weak in the cytoplasm of synaptic terminals, labelling being predominantly associated with the membrane compartment. In light-adapted cells, immunoreactivity is diffusely distributed throughout the terminal. Western blot analysis has revealed a reduction of pPKC alpha immunoreactivity in cytosolic fractions of homogenized dark-adapted retinae compared with light-adapted retinae. Pharmacological experiments with the isoform-specific PKC blocker Goe6976 have shown that inhibition of the enzyme influences immunolabelling for pPKC alpha, mimicking the effects of light on the subcellular distribution of immunoreactivity. Our findings suggest that the state of adaptation modifies the subcellular localization of a signalling molecule (PKC alpha) at the ribbon-type synaptic complex. We propose that changes in the subcellular distribution of PKC alpha immunoreactivity might be one component regulating the strength of the signal transfer of the bipolar cell terminal.

Retinal glutamate transporter activity persists under simulated ischemic conditions

Elevated extracellular concentrations of the neurotransmitter glutamate are neurotoxic and directly contribute to CNS damage as a result of ischemic pathologies. However, the main contributors to this uncontrolled rise in glutamate are still unconfirmed. It has been reported that the reversal of high-affinity glutamate transporters is a significant contributing factor. Conversely, it has also been observed that these transporters continue to take up glutamate, albeit at a reduced saturation concentration, under ischemic conditions. We sought to determine whether glutamate transporters continue to remove glutamate from the extracellular space under ischemic conditions by pharmacologically modulating the activity of high-affinity retinal glutamate transporters during simulated ischemia in vitro. Retinal glutamate transporter activity was significantly reduced under these ischemic conditions. The suppression of retinal glutamate transporter activity, with the protein kinase C inhibitor chelerythrine, significantly reduced ischemic glutamate uptake and enhanced retinal neurodegeneration. These findings imply a limited but protective role for retinal glutamate transporters under certain ischemic conditions, suggesting that pharmacological enhancement of high-affinity glutamate transporter activity may reduce tissue damage and loss of function resulting from toxic extracellular glutamate concentrations.

Lipophilic fraction of Panax ginseng induces neuronal differentiation of PC12 cells and promotes neuronal survival of rat cortical neurons by protein kinase C dependent manner

Panax ginseng is a traditional Chinese herb with a wide range of therapeutic benefits. Recent studies focusing on its effect on the central nervous system have revealed that ginseng has neurotrophic effects including differentiation of neurons. However, most studies involve use of the water-soluble fraction called saponin, and little is known about the effect of the lipophilic fraction. In the present study, we have shown that the lipophilic fraction of ginseng at a concentration of between 0.1 and 50 microg/ml can induce neurite outgrowth of PC12 cells in a dose-dependent manner. Nearly all cells showed morphological differentiation in response to the lipophilic fraction. This morphological differentiation of PC12 cells appeared to be similar to that of NGF. The lipophilic fraction of ginseng also induced neurite extension and promoted survival of rat cortical neurons at a concentration of between 0.025 and 1 microg/ml. These neurotrophic effects on PC12 cells and cortical neurons were not inhibited by K252b, which selectively blocks neurotrophin actions by inhibiting trk-type receptor tyrosine phosphorylation. This suggests that trks do not participate in the neurotrophic action of the lipophilic fraction. However, the effects were completely attenuated by sphingosine, polymyxin B or staurosporin, known inhibitors of protein kinase C (PKC) and calmodulin-dependent kinases. Our results suggest that the lipophilic fraction of ginseng exerts its neurotrophic effects via PKC-dependent pathways.

Increase in the pool size of releasable synaptic vesicles by the activation of protein kinase C in goldfish retinal bipolar cells

Secretion from neurons and neuroendocrine cells is enhanced by the activation of protein kinase C (PKC) in various preparations. We have already reported that transmitter (glutamate) release from Mb1 bipolar cells in the goldfish retina is potentiated by the activation of PKC. However, it is not yet settled whether the potentiation is ascribed to the increase in the pool size of releasable synaptic vesicles or in release probability. In the present study, Ca2+ influx and exocytosis were simultaneously monitored by measuring the presynaptic Ca2+ current and membrane capacitance changes, respectively, in a terminal detached from the bipolar cell. The double pulse protocol was used to estimate separately the changes in the pool size and release probability. The activation of PKC by phorbol 12-myristate 13-acetate (PMA) specifically increased the pool size but not the release probability. PKC was activated by PMA even after the Ca2+ influx was blocked by Co2+. In bipolar cells the releasable pool can be divided into two components: one is small and rapidly exhausted, and the other is large and slowly exocytosed. To identify which component is responsible for the increase in the pool size, the effects of PMA and a PKC-specific inhibitor, bisindolylmaleimide I (BIS), on each component were examined. The slow component was selectively increased by PMA and reduced by BIS. Thus, we conclude that the activation of PKC in Mb1 bipolar cells potentiates glutamate release by increasing the pool size of the slow component.

Diurnal and circadian variation of protein kinase C immunoreactivity in the rat retina

We studied the dependence of the expression of protein kinase C immunoreactivity (PKC-IR) in the rat retina on the light:dark (LD) cycle and on circadian rhythmicity in complete darkness (DD). Two anti-PKC alpha antibodies were employed: One, which we call PKCalphabeta recognized the hinge region; the other, here termed PKCalpha, recognized the regulatory region of the molecule. Western blots showed that both anti-PKC antibodies stained an identical single band at approximately 80 kD. The retinal neurons showing PKC-IR were rod bipolar cells and a variety of amacrine neurons. After 3 weeks on an LD cycle, PKCalphabeta-IR in both rod bipolar and certain amacrine cells manifested a clear rhythm with a peak at zeitgeber time (ZT) of 06-10 hours and a minimum at ZT 18. No rhythm in total PKC-IR was observed when using the PKCalpha antibody, but, at ZT 06-10 hours, rod bipolar axon terminals showed increased immunostaining. After 48 hours in DD, with either antibody, rod bipolar cells showed increased PKC-IR. The PKCalpha antibody alone revealed that, after 48 hours, AII amacrine neurons, which lacked PKC-IR in an LD cycle, manifested marked PKC-IR, which became stronger after 72 hours. Light administered early in the dark period greatly increased PKCalphabeta-IR in rod bipolar and some amacrine neurons. Our data indicate that light and darkness exert a strong regulatory influence on PKC synthesis, activation, and transport in retinal neurons.

Signal transduction mechanisms involved in ischemic preconditioning in the rat retina in vivo

Ischemic preconditioning (IPC) protects the rat retina against the injury that ordinarily follows severe ischemia. We showed previously that release of adenosine and de novo protein synthesis were required for IPC protection. The mechanisms of IPC were studied in the rat retina by examining the signal transduction mediators responsible, in particular, those theorized to be downstream of adenosine receptors. In addition, we examined the hypothesis that nitric oxide and hydroxyl radicals were involved in the IPC protective phenomenon. Retinal ischemia was produced for 60 min in ketamine/xylazine-anesthetized Sprague-Dawley rats, and recovery was measured using electroretinography. We tested the effects on the protective effect of IPC resulting from antagonism of protein kinase C, potassium ATP channels, nitric oxide synthase, or hydroxyl radicals. The effects of the inhibition of de novo protein synthesis or of protein kinase C, and blockade of potassium ATP channels on the mimicking of IPC by adenosine receptor agonists was examined.IPC protection was strongly attenuated by inhibition of protein kinase C and by blockade of potassium ATP channels, but unaffected by the inhibition of hydroxyl radicals. Blockade of nitric oxide synthase produced a trend toward enhancement of IPC protection. Mimicking of IPC protection by adenosine receptor agonists was inhibited by blockade of protein synthesis or of protein kinase C, as well as by potassium ATP channel antagonism. These results demonstrate that protein kinase C and potassium ATP channels are mediators of the protective effect produced by IPC. In addition, the results show that stimulation of adenosine receptor subtypes A1 and A2a is responsible for IPC protection via downstream stimulation of protein kinase C, the opening of potassium ATP channels, and de novo protein synthesis.

Protein kinase C-like immunoreactive cells in embryo and adult chicken retinas

Morphological evidence of a temporal parallelism between the appearance of the alpha isoform of protein kinase C (PKC) and some processes such as synaptogenesis in the plexiform layers of the chicken retina is offered. Immunostaining experiments were performed throughout embryonic, young and adult chicken life. The results help to understand the development of rod bipolar cells.

Localisation of the GABA(C) receptors at the axon terminal of the rod bipolar cells of the mouse retina

In the vertebrate retina, the rod bipolar cells make reciprocal synapses with amacrine cells at the axon terminal. Amacrine cells may perform a fine control of the transmitter release from rod bipolar cells by means of GABAergic synapses acting on different types of GABA receptors. To clarify this possibility GABA-induced currents were recorded by the patch-clamp whole cell method in rod bipolar cells enzymatically dissociated from the mouse retina. All cells tested showed a desensitising chloride-sensitive GABA-induced current. When GABA 30 microM was applied in presence of 100 microM biccuculine, a blocker of the GABA(A) receptors, a slow-desensitising component of the current still remains. This current was blocked when GABA 30 microM was applied in presence of 100 microM 3-aminopropylphosphonic acid, an antagonist of the GABA(C) receptors. The current mediated by GABA(C) receptors showed an EC50 of less that 5 microM; the ionic current through the GABA(A) receptor showed an EC50 of ca. 30 microM. Two pieces of evidence demonstrated that the GABA(C)-mediated current was localised at the axon terminal of rod bipolar cells: (1) cells lacking the axon terminal only showed the biccuculine-sensitive GABA-induced current; and (2) after mechanical section of the axon terminal, bipolar cells lost the slow-desensitising component of the GABA-induced current. We conclude that the rod bipolar cells express two types of ionotropic GABA receptors, and that the high sensitive GABA(C) receptors are mainly localised at the level of the axon terminal and therefore may contribute to the modulation of the transmitter release from the rod bipolar cell.

Differential localization and expression of alpha and beta isoenzymes of protein kinase C in the rat retina

Expression and cellular localization of three isoenzymes of Ca2+-dependent protein kinase C (PKCalpha, PKCbeta, and PKCgamma) in the adult rat retina were revealed by immunohistochemistry and in situ hybridization histochemistry with isoenzyme-specific antibodies and cRNA probes. Immunoreactivities and mRNA signals for PKCalpha were conspicuous in rod bipolar cells. A subgroup of amacrine cells expressed PKCalpha. The cells in the ganglion cell layer also displayed PKCalpha gene products. Positive immunoreactivities for PKCbeta were localized as stripe patterns in the inner plexiform layer, corresponding to the stratification levels of axon terminals of cone bipolar cells. The somata of cone bipolar cells expressed PKCbeta. Amacrine cells and retinal ganglion cells also displayed PKCbeta gene products. The results obtained by immunohistochemistry were confirmed with colocalization of mRNA signals for PKCalpha and PKCbeta on the somata. The cell membranes showed stronger immunoreactivities than did the cytoplasms for both PKCalpha and PKCbeta. Neither immunoreactivities nor mRNA signals for PKCgamma were detected in all retinal regions. The differential roles of Ca2+-dependent PKC isoenzymes could be revealed in physiological defined retinal neurons.

Phosphorylation of rod outer segment proteins modulates phosphatidylethanolamine N-methyltransferase and phospholipase A2 activities in photoreceptor membranes

The activities of enzymes involved in lipid metabolism--phospholipase A2 (PLA2) and phosphatidylethanolamine N-methyltransferase (PE N-MTase)--were found to be differently affected by pre-incubation of rod outer segments (ROS) under protein phosphorylating or dephosphorylating conditions. Exposure to cAMP-dependent protein kinase (PKA), under dark or light conditions, produced a significant increase in PE N-MTase activity, whereas PLA2 activity decreased. Under standard protein kinase C (PKC) phosphorylating conditions in light, PE N-MTase activity was stimulated and PLA2 activity was not affected. When the assays were performed in the dark, both enzymatic activities were unaffected when compared to the corresponding controls. Incubation of ROS membranes in light in the presence of PKC activators phorbol 12,13-dibutyrate (PDBu) and dioctanoylglycerol (DOG) resulted in the same pattern of changes in enzyme activities as described for standard PKC phosphorylating condition. Pre-incubation of membranes with the PKC inhibitor H-7 reduced the stimulation of PDBu on PE N-MTase activity, and had no effect on PLA2 activity in ROS membranes incubated with the phorbol ester. Pre-treatment of isolated ROS with alkaline phosphatase resulted in decreased PE N-MTase activity and produced a significant stimulation of PLA2 activity under dark as well as under light conditions when compared to the corresponding controls. These findings suggest that ROS protein phosphorylation and dephosphorylation modulates PE N-MTase and PLA2 activities in isolated ROS, and that these activities are independently and specifically modulated by particular kinases. Furthermore, dephosphorylation of ROS proteins has the opposite effect to that produced by protein phosphorylation on the enzymes studied.

Protection against glutamate neurotoxicity in retinal cultures by acidic conditions

We evaluated the effects of extracellular acidic conditions on glutamate-induced death in cultured retinal neurons. Primary retinal cultures, obtained from 3- to 5-day-old Wistar rats, were estimated to be consisted of mainly amacrine cells (90%) together with a small population of horizontal (8%) and ganglion cells (2%). We examined the effects of acidic pH (pH 6.0 to 7.0) on glutamate neurotoxicity by monitoring the delayed death of retinal neurons induced by brief (10 min) exposure to 1 mM glutamate followed by a 24-hr incubation. The glutamate-induced delayed death of cultured retinal neurons was attenuated with an acidic pH between 6.0 and 7.0. Furthermore, whole-cell patch-clamp recordings were taken from retinal neurons to examine the effects of acidic pH on N-methyl-D-aspartate (NMDA) or kainate receptor-mediated currents. NMDA- and kainate-induced currents were suppressed at pH 6.0 to 7.0 and pH 6.0 to 6.5, respectively. The acidity of the medium protected the retinal neurons from glutamate-induced delayed death, probably by inhibiting NMDA and/or kainate receptor activation.

Quantitative measurement of protein kinase C immunoreactivity in rod bipolar cells of the goldfish retina

The intensity of the immunohistochemical reaction (IIR) against the alpha species of protein kinase C (PKC) was quantified in the rod bipolar cells (RBC) of the goldfish retina using of image analysis. Retinae incubated in control Ringer solution showed similar IIR in both the soma and the axon terminal (IIR-ratio approximately 1). Activation of PKC induces the 'transport' of the enzyme to the synaptic terminal of RBC and an increase in the IIR-ratio. In the present report, the effect of retinal neurotransmitters on the IIR-ratio and the time course of PKC transport was studied.

Retinal neurones containing kainate receptors are influenced by exogenous kainate and ischaemia while neurones lacking these receptors are not -- melatonin counteracts the effects of ischaemia and kainate

The present experiments were carried out on three types of neurone in primary rabbit retinal cultures. One cell-type, bipolar neurones, have glutamate APB-type metabotropic receptors and can be identified by the presence of thetaPKC-immunoreactivity. The other two cell-types are primarily amacrine cells and can be 'stained' for the localisation of GABA immunoreactivity or for serotonin taken up from the medium. Most of the serotonin-accumulating and GABA-containing neurones contain glutamate kainate-type receptors. Exposure of the cultures to treatment of kainate (50 microM) or experimental ischaemia (8 h followed by 16 h reoxygenation) produced essentially similar findings. The serotonin-accumulating and GABA cells were affected as they were drastically reduced in numbers while the numbers of thetaPKC-containing cells were unaffected. Inclusion of the kainate/AMPA antagonist CNQX (100 microM) or melatonin (100 microM) to the medium during kainate or ischaemia treatments largely prevented the detrimental influences on the serotonin-accumulating and GABA cells. It is concluded that during experimental ischaemia excessive glutamate is released to influence cells which contain kainate and APB-type receptors. However, only the neurones containing the kainate receptors are negatively affected with the generation of free radicals. Melatonin or CNQX protects against this effect by scavenging free radicals or acting at the receptor level, respectively.

Two classes of bipolar cell in the retina of the skate Raja erinacea

We have used immunoreactions against serotonin and protein kinase C to visualize two distinct classes of bipolar cell in the all-rod retina of the skate, Raja erinacea. To enhance the immunoreaction in serotonin-accumulating bipolar cells, prior to fixation, some retinas were incubated in Ringer's solution containing serotonin and pargyline. We found the somata of serotonin-accumulating bipolar cells to be located slightly distal to the midline of the inner nuclear layer. With increasing eccentricity from the visual streak, the size of the perikarya increases, concomitant with a decline in density of their distribution. Dendrites emanate from stout primary stalks and branch out before reaching the outer plexiform layer. Axons are bistratified within the inner plexiform layer with ramifications at the border of strata 1 and 2 and in stratum 4. The overall morphology of serotonin-accumulating bipolar cells is similar to that of serotonin-accumulating OFF bipolar cells of other non-mammalian vertebrates. Protein kinase C immunoreactive cells display the typical appearance of rod bipolar cells. Somata of protein kinase C immunoreactive bipolar cells are spindle-shaped and located distal to the serotonin-accumulating bipolar cells. Dendrites of these bipolars do not ramify before reaching the outer plexiform layer. Thin axons of protein kinase C immunoreactive bipolar cells end in large, club-shaped terminals in stratum 5 of the inner plexiform layer, bearing a striking similarity to axon terminals of mammalian ON rod bipolar cells. Our findings suggest that the all-rod retina of the skate contains at least two distinct vertical pathways including an OFF bipolar cell pathway in addition to a classical rod ON bipolar pathway.

Dawn, diacylglycerol, calcium, and protein kinase C--the retinal wrecking crew. A signal transduction cascade for rhabdom shedding in the Limulus eye

Vertebrate and invertebrate photoreceptors shed their photosensitive membrane on a daily basis. Although we have detailed knowledge of the morphology of the disc shedding and renewal process in vertebrate photoreceptors, and of the turnover of rhabdom in invertebrate photoreceptors, we know relatively little about the molecular mechanisms whereby these processes are triggered by light and/or by circadian efferent input to the retina. We have used the horseshoe crab, Limulus polyphemus, as a model system to unravel the molecular means by which the trigger light is communicated to the intracellular machinery responsible for the daily breakdown of the photosensitive membrane. Phorbol esters, potent and specific activators of protein kinase C (PKC), induce a robust burst of rhabdom shedding when injected subretinally into the compound lateral eye of Limulus. This occurs in the absence of the light trigger normally required to initiate shedding in the lateral eye at dawn, suggesting that PKC may play a role in the light triggering of rhabdom shedding. Diacylglycerol (DAG) analogs were also found to elicit rhabdom shedding in the lateral eye without a light trigger, but at uncharacteristically high concentrations. However, injecting inositol trisphosphate (InsP3) and DAG analog simultaneously results in a tenfold decrease in the concentration of DAG analog required to initiate a shedding event. Immunohistochemical screening for PKC in the lateral eye shows that two isozymes (PKC beta II and PKC zeta) are co-localized to the retinular cell rhabdom. Taken together, these data suggest that light triggers rhabdom shedding at dawn via a classical Ca(2+)-sensitive PKC, similar to PKC beta II, which is activated synergistically by the light-evoked production of DAG and InsP3.

The occurrence of protein kinase C theta and lambda isoforms in retina of different species

The localization and immunochemical identification of the novel protein kinase C theta (nPKC theta) and the atypical protein kinase C lambda (aPKC lambda) isoforms in retinas of different species were analyzed by immunohistochemistry and SDS-PAGE/Western blotting. nPKC theta immunoreactivity is associated with bipolar cells of mammalian (rabbit, rat and guinea pig) retinas but not the non-mammalian goldfish retina which has a lower concentration of nPKC theta. However, SDS-PAGE and Western blotting data indicate the antigen recognized by the nPKC theta monoclonal antibody in the retina is of a lower molecular weight than that expected for nPKC theta. This would suggest nPKC theta is more susceptible to degradation/breakdown than other PKC isoforms found in the retina or that the nPKC theta antibody may be recognizing an unknown retinal antigen. A comparison of nPKC theta and cPKC alpha immunoreactivities in bipolar cells shows unique distributions exist for the two isoforms. nPKC theta is present in the developing retina at an earlier stage than cPKC alpha. The typical 'transport' of cPKC alpha toward axonal terminals by phorbol-12,13-dibutyrate does not occur for nPKC theta yet both are translocated from the cytosolic to membrane compartments. The inner plexiform layer and the inner nuclear layer (putative horizontal cells) of all species examined (rabbit, rat, guinea pig and goldfish) exhibited positive immunoreactivity for aPKC lambda as confirmed by SDS-PAGE/Western blotting.

The influence of experimental ischaemia on protein kinase C and the GABAergic system in the rabbit retina

Pressure-induced ocular ischaemia followed by 25-28 hr of reperfusion to the rabbit retina drastically reduces or eliminates the b-wave of the electroretinogram and results in all the GABA from the amacrine cells being released, as judged by immunohistochemistry. Some of these GABA cells have the capacity to take-up exogenous serotonin and these GABA/serotonin cells have kainate/AMPA receptors. Previous studies have shown that an ischaemic insult causes these receptors to be stimulated to produce a release of the cells' GABA. The majority of the GABA/serotonin cells are also incapable of taking-up exogenous serotonin after ischaemia, which suggests that they are irreversibly damaged. However, there was still a minority of the cells which accumulated serotonin, which shows that neurones containing kainate/AMPA receptors are not irreversibly damaged at the same rate by ischaemia. The "staining" patterns for GABAA-receptor and GABA immunoreactivities in the rabbit retina are very similar and following ischaemia the GABAA-receptor immunoreactivity was reduced in intensity and became patchy in nature. It is not known whether this result reflects a down-regulation of the GABAA-receptors caused by the released GABA or a destruction of cells containing the GABAA-receptors. The ischaemic conditions used caused patchy, irregular and inconsistent signs of histological damage to the retina, even in areas of similar eccentricity, suggesting this parameter should be used with caution when judging the severity of an ischaemic insult. alpha-Protein kinase C (alpha PKC) present in the on-bipolar cells which have glutamate metabotropic APB receptors is both reduced or down-regulated and translocated by ischaemia. This is also the case for delta PKC which is absent from the on-bipolar cells. These data were established by a combination of immunohistochemistry and electrophoresis/blotting experiments. Enzyme analysis also showed that all PKC calcium-dependent and -independent isoenzymes, are translocated and reduced by ischaemia making it difficult to judge whether PKC inhibitors may be appropriate anti-ischaemic agents.

Prolonged bilateral carotid artery occlusion induces electrophysiological and immunohistochemical changes to the rat retina without causing histological damage

Reduction of the retinal blood flow by occlusion of both common carotid arteries suppressed the b-wave of the rat's electroretinogram. Transient occlusion of the carotids for 45 min reduced the b-wave by 46% without affecting the amplitude of the a-wave. The normal ERG activity returned 30 min after restoration of blood flow. Prolonged carotid occlusion for 7 days totally abolished the b-wave but enhanced the a-wave amplitude. Although b-wave amplitude suppression has been considered as an indicator of retinal ischaemia, no histological changes were seen in retinas of rats subjected to 45 min or 7 days of two-vessel occlusion, when observed by light microscopy. Moreover, GABA, GABAA receptor, calretinin and PKC-alpha immunoreactivities were unaltered. Carotid artery occlusion did, however, induce the expression of the cytoskeletal protein, glial fibrillary acidic protein (GFAP), in retinal Müller cells. The increase in the Müller cell GFAP immunoreactivity was related to how long the carotids were occluded as well as the reperfusion time. Prolonged occlusion for 7 days resulted in a 356% increase in retinal GFAP. These findings show that a reduction of retinal blood flow by occlusion of the carotids causes a metabolic stress to the retina and elicits events associated with gliosis without resulting in 'ischaemic-like' morphological changes.

The effect of kainate on protein kinase C, GABA, and the uptake of serotonin in the rabbit retina in vivo

The purpose of this study was to investigate the effect of kainate on protein kinase C (PKC), gamma-aminobutyrate (GABA) and serotonin uptake in the rabbit retina. Kainate when injected into the vitreous humour produces a change in the GABA immunoreactivity within 6 hours. After 3 days, remnants of the normal GABA immunoreactivity still persist and additionally astrocyte and microglia-like elements "stain" positively for GABA. After 7 days exposure to kainate none of the normal GABA immunoreactivity is apparent, instead a number of round-shaped elements which may be reactive astrocytes and/or microglia stain positively for GABA. During these stages kainate does not affect the alpha PKC immunoreactivity associated with the on-bipolar cells. Six hours following kainate treatment the ability of certain GABA amacrine cells to take up exogenous serotonin is unaffected. After three days only a few of these cells can still take up exogenous serotonin and then not avidly. After seven days the GABA/serotonin amacrine cells cannot take up exogenous serotonin suggesting that all of these neurons are irreversibly damaged. One hour after treatment with kainate both calcium-dependent and -independent PKC species are translocated from the cytosolic to membrane compartments. After 5 hours and 7 days there was also evidence from the enzyme assay experiments that kainate caused the calcium-dependent and -independent PKC enzymes to be translocated but because the total enzyme activity was reduced due perhaps to down-regulation of the enzyme this was difficult to assess precisely.(ABSTRACT TRUNCATED AT 250 WORDS)

Two types of mitochondria are evidenced by protein kinase C immunoreactivity in the Müller cells of the carp retina

The localization of protein kinase C (PKC) was studied immunocytochemically in the Müller cells of the carp retina. Electron microscope immunocytochemistry (using a monoclonal antibody to the alpha and beta isoenzymes of PKC) showed PKC-immunoreactivity mainly inside some mitochondria, especially along the mitochondrial cristae whereas other mitochondria in the same Müller cells showed no staining. Despite a detailed analysis we did not find any significant morphological difference between labeled and unlabeled mitochondria. These results demonstrate, for the first time, the presence of PKC immunoreactivity inside mitochondria and suggest that individual mitochondria may differ in signal transduction pathway.

Localization of protein kinase C subspecies in the rabbit retina

The localization of PKC subspecies alpha, beta, gamma, epsilon and zeta was studied immunocytochemically in the rabbit retina. Conventional, Ca(2+)-sensitive PKC subtypes alpha, beta, gamma were all localized in different neuronal populations. The zeta-subspecies, which does not require Ca2+ for activation, was colocalized with PKC-alpha. PKC-epsilon, which is independent of Ca2+ and DAG, was colocalized with PKC-beta. Some populations of neurons, including cone bipolar cells, contained none of the PKC-subspecies studied. These results imply a cellular segregation of different signaling pathways in mammalian retina.

The occurrence of three calcium-independent protein kinase C subspecies (delta, epsilon and zeta) in retina of different species

The localisation and immunochemical identification of three different forms of calcium-independent protein kinase C (PKC-epsilon, PKC-delta and PKC-zeta) in retinas of different species were analysed by immunohistochemistry and SDS-PAGE/Western blotting, respectively. More than one component of different molecular weights reacted with the polyclonal antibodies in all retinal samples though in all instances a component of molecular weight corresponding to the individual PKCs was recognised and could be eliminated or reduced by preincubating the primary antibodies with the peptides used to generate the antibodies. PKC-zeta immunoreactivity was exclusively associated with the inner segments of the photoreceptors in both mammalian (guinea-pig, rabbit, rat) and non-mammalian (goldfish, chick) retinas. PKC-epsilon immunoreactivity is present in bipolar cells, particularly in their terminals of mammalian and goldfish retinas. In the chick retina immunoreactivity for this enzyme and for PKC-delta was with the inner segments of the photoreceptors. The Müller cells in mammalian retinas and a sub-population of ganglion cells in the goldfish retina exhibited positive immunoreactivity for PKC-delta. The immunoreactivities for all the PKC isoenzymes were eliminated or drastically reduced when the primary antibodies were first preincubated with the peptides used to generate the antibodies.

Inositol-1,4,5-trisphosphate receptors in the vertebrate retina

Evidence has shown an activation of phosphatidylinositol 4,5-bisphosphate (PIP2) specific phospholipase C (PtdIns-PLC) by light in the vertebrate retina and rod outer segments (ROS), suggesting important roles for its two metabolites, 1,2-diacylglycerol (DG) and inositol-1,4,5-trisphosphate [Ins(1,4,5)P3]. DG activates protein kinase C (PKC) and Ins(1,4,5)P3 releases bound intracellular calcium. Since Ca2+ plays an important role in light adaptation, the presence of Ins(1,4,5)P3 receptors in ROS may indicate a regulatory role of Ins(1,4,5)P3 to the free Ca2+ content. In the present study, we investigated the Ins(1,4,5)P3 receptors in whole retinal membranes and several subcellular fractions prepared from bovine retinas. Scatchard analyses of binding data for retinal membrane preparations showed a single, high-affinity binding site with equilibrium dissociation constant (Kd) of 24 +/- 2 nM and maximal binding capacity (Bmax) of 353 +/- 15 fmol/mg protein at pH 7.4. Specific binding was found in both small and large synaptosomal preparations representing inner and outer plexiform layers, respectively. A detectable, but low abundance of Ins(1,4,5)P3-specific binding in ROS was observed at both pH 7.4 and 8.3, but no specific binding of Ins(1,4,5)P3 was found in isolated outer segment discs. The binding of Ins(1,4,5)P3 in ROS was reduced by addition of ATP, suggesting a regulatory role for this nucleotide. Addition of calcium, sodium, and potassium ions also reduced specific binding of Ins(1,4,5)P3. Immunocytochemical studies indicate intense staining in the inner segment and extending to the ROS. Inner and outer plexiform layers were also stained. These findings show that the Ins(1,4,5)P3 receptor is present in photoreceptor cells and inner and outer plexiform layers in the vertebrate retina.

Protein kinase C-epsilon is a developmentally regulated, neuronal isoform in the chick embryo central nervous system

Protein kinase C (PKC) is expressed as many isoforms and in high quantities in the central nervous system (CNS), which suggests an important role for this enzyme in neuronal development and function. We used specific antibodies to investigate the expression of the known PKC isoforms in extracts from chick major CNS areas during embryogenesis, from day 3 (E3) of incubation to day 1 post-hatching (P1). PKC-epsilon was the predominant isoform and was expressed from E6 onward in all brain regions, except retina (E12 and on). PKC-alpha/beta and -zeta isoforms were expressed at lower levels prior to PKC-epsilon expression and throughout embryogenesis. No other isoforms were detected in neural tissue preparations. We then used neural culture systems derived from the chick CNS to study the expression of PKC isoforms in neuroblasts, cortical neurons, and cortical glial cells. Western blotting and immunostaining of neuroblast-enriched cultures, derived from E3 CNS, showed only the Ca(2+)-dependent PKC-alpha/beta to be present. Studies on neuronal cultures derived from E6 cerebral hemispheres revealed only the Ca(2+)-independent PKC-epsilon to be expressed in neurons, as predicted by the developmental studies on tissue homogenates. PKC-epsilon immunoreactivity was seen intracellularly in differentiating neurons, regardless of their neurotransmitter phenotypes, and it correlated well with the level of neuronal activity. Furthermore, PKC-alpha/beta immunoreactivity was verified on glia cells, as the glial lineage emerges in E15 cortical cultures. These data suggest that PKC-epsilon expression is associated with the final neuroblast division in neurons, and the correlation of PKC isoform expression and neural cell lineage is discussed.

An intraocular injection of kainate induces expression of c-fos-like protein and activation of protein kinase C (alpha) in specific rabbit retinal neurones

Intraocular injection of kainate into the rabbit eye causes both a translocation and transport of the bipolar cell's alpha PKC 6 h later. Although this effect is similar to what occurs for the phorbol ester, phorbol 12,13-dibutyrate (PDbut), it shows specificity in that N-methyl-D-aspartate (NMDA), 5,7-dihydroxytryptamine and 2-amino-4-phosphonobutyrate (APB) are ineffective. However, preliminary experiments suggest that, when injected into the eye, quisqualate also influences the alpha PKC of the bipolar cells. Injection of kainate into the rabbit eye shows that c-fos-like protein is expressed in certain amacrine and ganglion but not in bipolar cells 6 h later. This expression of c-fos immunoreactivity is transient because 15 h after the injection of kainate no positive staining was seen. It was not possible to analyse the kainate-induced c-fos expression for periods of less than 6 h because the anaesthetic used, Hypnorm, induced c-fos-like protein expression which lasted for 2-4 h.

The occurrence of three isoenzymes of protein kinase C (alpha, beta and gamma) in retinas of different species

The localisation and immunochemical identification of 3 different forms of protein kinase C (PKC-alpha, PKC-beta and PKC-gamma) in retinas of different species were analysed by immunohistochemistry and SDS-PAGE-Western blotting, respectively. Only in some cases was there a correlation between the findings from each procedure. One reason for the lack of correlation could be the small amounts of PKC present in some retinas, which made detection possible only by first concentrating the antigen by SDS-PAGE and then carrying out Western blotting. Another possible reason is that an antibody recognises unknown antigens immunohistochemically, but, because of their specific characteristics, they are denatured when subjected to SDS-PAGE and Western blotting and therefore remain undetected. PKC-beta immunoreactivity is present in rabbit, frog and goldfish retinas but absent from the rat retina. However, SDS-PAGE and Western blotting experiments showed that the PKC-beta isoenzyme is absent from the fish retina but present in the rat retina. PKC-beta immunoreactivity in rabbit retina is present in ganglion and/or amacrine cells; in the frog retina the enzyme is associated with some bipolar cells. In the goldfish retina, PKC-beta is associated with a large population of cells in the ganglion cell layer as well as with some amacrine cell bodies. PKC-alpha is present primarily in bipolar cells of rat, fish and rabbit retinas and was not detected by immunohistochemistry or blotting experiments in the frog retina. SDS-PAGE and Western blotting of retinal extracts from different species showed that PKC-gamma occurs in the rabbit where it was associated with ganglion and/or amacrine cells.(ABSTRACT TRUNCATED AT 250 WORDS)