Cryopreservation of postnatal rat retinal ganglion cells: persistence of voltage- and ligand-gated ionic currents

Cryopreservation of granule cells from the postnatal rat hippocampus

Although primary cultures of neurons are essential methods for cell biological and pharmacological researches, many animals must be sacrificed for each experiment. Here we introduce a novel system to cryopreserve hippocampal granule cells (GCs) prepared from postnatal rats. Being thawed after as long as 60 days of cryopreservation, GCs expressed the mature neuronal marker MAP-2 and elongated single tau-1-positive axons and multiple tau-1-negative dendrites. These properties closely resembled intact GCs in primary cultures, providing the advantage of being able to repeatedly prepare stable cultures with a single sacrifice of animals.

A patch-clamp investigation of membrane currents in a novel mammalian retinal ganglion cell line

We characterised membrane currents in undifferentiated RGC-5 cells, a cell line used in in vitro models of apoptosis and glaucoma. The cells were inexcitable, with no voltage-dependent Na(+) currents or action potentials. Some novel currents were observed including basal Cl(-) currents, inwardly rectifiying K(+) currents and Gd(3+) insensitive stretch-activated currents. Our results highlight the differences between the electrophysiological properties of undifferentiated RGC-5 cells and retinal ganglion cells.

Molecular basis of glutamate toxicity in retinal ganglion cells

Loss of retinal ganglion cells (RGCs) is a hallmark of many ophthalmic diseases including glaucoma, retinal ischemia due to central artery occlusion, anterior ischemic optic neuropathy and may be significant in optic neuritis, optic nerve trauma, and AIDS. Recent research indicates that neurotoxicity is caused by excessive stimulation of receptors for excitatory amino acids (EAAs). In particular, the amino acid glutamate has been shown to act as a neurotoxin which exerts its toxic effect on RGCs predominantly through the N-methyl-D-aspartate (NMDA) subtype of glutamate receptor. NMDA-receptor-mediated toxicity in RGCs is dependent on the influx of extracellular Ca2+. The increase in [Ca2+]i acts as a second messenger that sets in motion the cascade leading to eventual cell death. Glutamate stimulates its own release in a positive feedback loop by its interaction with the non-NMDA receptor subtypes. Ca(2+)-induced Ca2+ release and further influx of Ca2+ through voltage-gated Ca2+ channels after glutamate-induced depolarization contribute to glutamate toxicity. In vitro and in vivo studies suggest that the use of selective NMDA receptor antagonists or Ca2+ channel blockers should be useful in preventing or at least abating neuronal loss in the retina. Of particular importance for future clinical use of NMDA receptor antagonists in the treatment of acute vascular insults is the finding that some drugs can prevent glutamate-induced neurotoxicity, even when administered a few hours after the onset of retinal ischemia.

The application of in vitro isolation, cryopreservation and patch-clamp microelectrode recording methods to adult rat thymic nurse cells

Characterisation of the ionic mechanisms possessed by immune cells has begun to reveal a range of transmembrane ion channel properties which may have immunological significance. Since thymic epithelial cells appear to influence selection of the T cell repertoire, understanding their membrane physiology may be of importance. A method is therefore outlined for the targeting of patch-clamp electrophysiological measurements to acutely isolated, fresh and cryopreserved adult rat thymic nurse cells. These cells represent a discrete and predominantly cortical population of epithelium. Cells were separated by enzymatic and mechanical dispersal of thymus, enriched by sedimentation and identified on the basis of their characteristic lympho-epithelial, multi-cellular morphologies. Phase-bright cells retaining this anatomical form survived freezing and the voltage-gated conductances in such cells are described. The merits of this approach include the preparation and storage of mature differentiated phenotypes of immune cells for in vitro studies. Their preservation permits temporal separation of experiments, correlative experimentation on identical samples, optimises cell preparation in terms of cost and labour, and reduces animal and tissue requirements.

Identification and localization of K+ channels in the mouse retina

Voltage-gated potassium channels are differentially expressed in the brain, and recent studies have shown that K+ channels show subcellular localization. We characterized the distribution of five different K+ channels in the mouse retina. Each channel was distributed in a unique pattern in the retina and was localized to specific subcellular domains within a given retinal neuron. Kv1.4 and Kv4.2 were consistently found in axonal and somatodendritic portions, respectively, consistent with previous studies in brain. In contrast, Kv1.2, Kv1.3, and Kv2.1 showed variable subcellular distribution depending upon cellular context. These results suggest that no one K+ channel is distributed over the entire length of the neuron to provide a "housekeeping" level of membrane potential stabilization. Instead, we propose that each K+ channel is associated with a specific subcellular functional module, and each local K+ conductance responds uniquely to local voltage and second messenger signals.

Co-expression of AMPA/kainate receptor-operated channels with high and low Ca2+ permeability in single rat retinal ganglion cells

The patch-clamp technique was used to record whole-cell currents induced by alpha-amino-3-hydroxyl-5-methyl-isoxazol-4-propionic acid (AMPA) or kainate in solitary rat retinal ganglion cells (n = 125) in vitro. Two groups of retinal ganglion cells could be distinguished according to their responses to kainate or AMPA in extracellular solutions with Ca2+ as the only permeant cation. The ratio of the steady-state currents evoked by a given concentration of AMPA compared to kainate was low (0.08) in the first group and high (0.61) in the second group of retinal ganglion cells. The Ca2+ permeability through AMPA/kainate receptor-operated channels was low (PCa2+/PCs+ < 0.1) in the first group (n = 74, 59%) and moderate (PCa2+/PCs+ = 0.53) in the second group (n = 51, 41%) of retinal ganglion cells. The fraction of the total current induced by stimulation of non-N-methyl-D-aspartate receptors that is flowing through Ca2+ permeable AMPA/kainate channels in single cells with high Ca2+ permeability was estimated by comparing the current-voltage relationship in extracellular solutions with either Ca2+ or Na+ as the sole charge carrier. The contribution of Ca(2+)-permeable channels to the non-N-methyl-D-aspartate receptor induced whole-cell current in single Ca2+ permeable cells (n = 12) ranged from 40 to 70%, correlating with the intermediate level of Ca2+ permeability (PCa2+/PCs+ = 0.22-0.80) measured by an independent method in these cells. Thus, single Ca(2+)-permeable cells appear to express at least two types of AMPA/kainate receptor-operated channels with high or low Ca2+ permeability. Using the polymerase chain reaction, transcripts for the glutamate receptor subunits 1-4, including their "flip" and "flop" versions, were identified in retinal ganglion cells. Together, these findings suggest that among rat retinal ganglion cells there are differences in the pattern of expression of AMPA/kainate receptor-operated channels. Moreover, individual cells co-express multiple heterologous non-N-methyl-D-aspartate receptors with distinct functional properties. The functional diversity of these receptors may play an important role in controlling Ca2+ entry into neurons. We speculate that the low Ca2+ permeability and the preference for kainate in one group of retinal ganglion cells may be due to the predominant expression of non-N-methyl-D-aspartate receptors containing the edited form of the glutamate receptor subunit 2 flop splice variant.

A slowly inactivating K+ current in retinal ganglion cells from postnatal rat

The whole-cell configuration of the patch-clamp technique was used to study voltage-gated K+ conductances in retinal ganglion cells from postnatal rat. Retinal ganglion cells were fluorescently labeled in situ, dissociated from the retina, and maintained in culture. With physiological solutions in the bath and the pipette, depolarizing voltage steps from physiological holding potentials activated Na(+)-(INa), Ca2+ (ICa), and K(+)-currents studied previously in retinal ganglion cells. Here we report on a slowly decaying K+ current, not heretofore reported in rat. With 4-AP, TEA, and Co2+ in the bath, to block IA, IK, and IK(Ca), respectively, a slowly decaying outward current was activated from -80 mV by steps positive to -40 mV. This current was present in 92% of all ganglion cells tested (n = 83). It activated within 10 ms and inactivated with a voltage-independent time constant of about 70 ms at 35 degrees C. Inactivation was voltage-dependent, half-maximal at -55 mV, and almost complete at 0 mV. The current was blocked by internal Cs+ and TEA, or by external application of 1 mM Ba2+, but not by 3 mM extracellular Co2+. The biophysical and pharmacological properties of this current are distinctly different from those of slowly inactivating K+ currents studied in other rat neurons. It was very similar, however, to a slowly inactivating K+ current previously reported in ganglion cells of tiger salamander retina. This last finding indicates conservation of a defined K+ channel type in functionally related cells in both lower vertebrates and mammals.