Calcium-binding proteins in whole brain and synaptic subfractions

Synergy between chronic corticosterone treatment and cerebral ischemia in producing damage in noncalbindinergic neurons

Administration of endogenous corticosterone to intact animals induces calbindin-D28k protein in the hippocampal CA1-CA2 subfields. The fact that this effect on calbindin-D28k was shown to be specific for the hippocampus argues for a receptor-mediated effect on gene expression. In addition, chronic pretreatment with corticosterone aggravates ischemia-induced neuronal damage in the CA3-CA4 subfields. This effect is similar to that of preischemic hyperglycemia, which also induces postischemic seizures and aggravates brain damage, since corticosterone raises blood glucose level and enhances tissue lactic acidosis during ischemia. The energetically compromising qualities of corticosterone indicates that it is a key factor in hippocampal vulnerability. We assume that the increase of calbindin-D28k expression in the CA1-CA2 subfields in corticosterone-treated animals is an adaptive response to the exogenous stress. The lack of adaptive response in CA3-CA4 neurons endangers them by impairing the ability of these neurons to counteract the deleterious effects of calcium. This finding, supports: (1) the hypothesis that corticosterone treatment, when paired with an ischemic insult, causes a prolonged elevation of neuronal [Ca2+]i, in an energy dependent manner, probably through the reduction of calcium efflux and (2) that neurons which do contain calbindin-D28k are particularly predisposed to ischemic insults. The CA1-CA2 neurons express high amounts of calbindin-D28k under stress conditions because their activity may involve a high rate of calcium buffering.

Ca(2+)-binding proteins in rat synaptic fractions surveyed by the 45Ca2+ overlay method

Ca(2+)-binding proteins in the synaptic and subsynaptic fractions (P2, synaptosome, synaptic plasma membrane, and postsynaptic density [PSD]-enriched fractions) and soluble fraction of rat brain were surveyed by a 45Ca2+ overlay method. The PSD-enriched fraction from cerebral cortex contained two major Ca(2+)-binding proteins (55,000 M(r) and 19,000 M(r)) and a distinct group (in 140,000 M(r) region), and two minor ones (66,000 M(r) and 16,000 M(r)); and the fraction from cerebellum contained two (55,000 M(r) and 19,000 M(r)). The proteins with 55,000 M(r) and 19,000 M(r) were identified as tubulin and calmodulin, respectively, and present in all the fractions investigated. The Ca(2+)-binding proteins of 140,000 M(r) region were found only in the PSD-enriched fraction isolated from cerebral cortex: neither the PSD-enriched fraction isolated from cerebellum nor other subcellular fractions prepared from cerebral cortex and cerebellum contained the proteins. The 140,000 M(r) Ca(2+)-binding proteins were the substrates for the Ca2+/calmodulin-dependent protein kinase II associated with PSD, and no change in the Ca(2+)-binding was detected by the 45Ca2+ overlay method after phosphorylation of the proteins by the protein kinase. The 16,000 M(r) Ca(2+)-binding protein might be the beta-subunit of calcineurin. Calretinin and calbindin-D28k were also detected as Ca(2+)-binding proteins in the soluble fractions of both cerebral cortex and cerebellum.

Calbindin-D28K and ischemic damage of pyramidal cells in rat hippocampus

An antibody against rat calbindin-D28K, a calcium-binding protein present at high concentration in certain neurons of the central and peripheral nervous systems, was used to determine the progression of the pathological events in the rat hippocampus following experimental cerebral ischemia. Calbindin-D28K immunoreactivity is present in dentate granule cells and in the CA1-CA2 pyramidal cells. CA1 subfield contains a higher proportion of calbindin-D28K-positive pyramidal cells than does the CA2 subfield and CA1 cells are more immunoreactive than the CA2 cells. The pyramidal cells of the CA1 and CA2 subfields are vulnerable to ischemia. The cells in the CA1 became necrotic within 3-4 days after ischemia while those of the CA2 became necrotic within 2 days. There was a concomitant decrease in calbindin-D28K immunoreactivity in the whole hippocampal regio superior after ischemia which peaked 3 days postischemia. The difference in CA2 and CA1 vulnerability seemed to be inversely correlated with the calbindin-D28K contents of the CA2 and CA1 pyramidal cells. The decrease in the calbindin-D28K contents of these neurons was accompanied by cell damage. We therefore suggest that calbindin-D28K is an important factor for the survival of pyramidal cells in the hippocampal formation after ischemia.

A reliable two-dimensional gel electrophoresis procedure for separating neural proteins

A facile two-dimensional gel electrophoresis procedure has been developed for the analysis of neural tissue proteins which eliminates the serious problems associated with protein insolubility at the point of sample application onto polymerized first-dimension isoelectric focusing gels. This was accomplished by combining the methods of two previously published procedures. Our procedure provides an alternative method to the complex gel systems often employed for less soluble proteins, and yields very reproducible, high resolution separations. This procedure, which is in routine use in our laboratories for the analysis of total proteins extracted from retina and brain, produces protein patterns that are easily compared using both visual and computer-assisted image analysis techniques. Presented here are the results of a set of experiments designed to identify proteins unique to retina. This procedure should be useful to investigators studying protein changes resulting from genetic mutation, development, drug treatment or disease, in neural tissue as well as in virtually all other tissues.

Calretinin: a gene for a novel calcium-binding protein expressed principally in neurons

A novel gene of the calmodulin superfamily, encoding a 29-kD neuronal protein here named "calretinin," has been isolated as a cDNA clone from chick retina. The encoded sequence includes four putative calcium-binding sites and a fusion protein binds calcium. The most similar protein known is the 28-kD intestinal calcium-binding protein, calbindin (58% homology). Both genes date from before the divergence of chicks from mammals. The distribution of calretinin and calbindin mRNAs in chick tissues has been mapped using RNA gel blots and in situ hybridization. RNAs from both genes are abundant in the retina and in many areas of the brain, but calretinin RNA is absent from intestine and other nonneural tissues. Calretinin and calbindin are expressed in different sets of neurons throughout the brain. Calretinin RNA is particularly abundant in auditory neurons with precisely timed discharges.