Effect of senescence on Ca2+-ion transport by heart mitochondria

Mitochondrial function in hypoxic ischemic injury and influence of aging

Mitochondria are a major target in hypoxic/ischemic injury. Mitochondrial impairment increases with age leading to dysregulation of molecular pathways linked to mitochondria. The perturbation of mitochondrial homeostasis and cellular energetics worsens outcome following hypoxic-ischemic insults in elderly individuals. In response to acute injury conditions, cellular machinery relies on rapid adaptations by modulating posttranslational modifications. Therefore, post-translational regulation of molecular mediators such as hypoxia-inducible factor 1α (HIF-1α), peroxisome proliferator-activated receptor γ coactivator α (PGC-1α), c-MYC, SIRT1 and AMPK play a critical role in the control of the glycolytic-mitochondrial energy axis in response to hypoxic-ischemic conditions. The deficiency of oxygen and nutrients leads to decreased energetic reliance on mitochondria, promoting glycolysis. The combination of pseudohypoxia, declining autophagy, and dysregulation of stress responses with aging adds to impaired host response to hypoxic-ischemic injury. Furthermore, intermitochondrial signal propagation and tissue wide oscillations in mitochondrial metabolism in response to oxidative stress are emerging as vital to cellular energetics. Recently reported intercellular transport of mitochondria through tunneling nanotubes also play a role in the response to and treatments for ischemic injury. In this review we attempt to provide an overview of some of the molecular mechanisms and potential therapies involved in the alteration of cellular energetics with aging and injury with a neurobiological perspective.

Age-related changes of myocardial ATP supply and demand mechanisms

In advanced age, the resting myocardial oxygen consumption rate (MVO2) and cardiac work (CW) in the rat remain intact. However, MVO2, CW and cardiac efficiency achieved at high demand are decreased with age, compared to maximal values in the young. Whether this deterioration is due to decrease in myocardial ATP demand, ATP supply, or the control mechanisms that match them remains controversial. Here we discuss evolving perspectives of age-related changes of myocardial ATP supply and demand mechanisms, and critique experimental models used to investigate aging. Specifically, we evaluate experimental data collected at the level of isolated mitochondria, tissue, or organism, and discuss how mitochondrial energetic mechanisms change in advanced age, both at basal and high energy-demand levels.

Limiting sarcolemmal Na+ entry during resuscitation from ventricular fibrillation prevents excess mitochondrial Ca2+ accumulation and attenuates myocardial injury

BACKGROUND

intracellular Na+ accumulation during ischemia and reperfusion leads to cytosolic Ca2+ overload through reverse-mode operation of the sarcolemmal Na+ -Ca2+ exchanger. Cytosolic Ca2+ accumulation promotes mitochondrial Ca2+ (Ca2+ m) overload, leading to mitochondrial injury. We investigated whether limiting sarcolemmal Na+ entry during resuscitation from ventricular fibrillation (VF) attenuates Ca2+ m overload and lessens myocardial dysfunction in a rat model of VF and closed-chest resuscitation.

METHODS

hearts were harvested from 10 groups of 6 rats each representing baseline, 15 min of untreated VF, 15 min of VF with chest compression given for the last 5 min (VF/CC), and 60 min postresuscitation (PR). VF/CC and PR included four groups each randomized to receive before starting chest compression the new NHE-1 inhibitor AVE4454B (1.0 mg/kg), the Na+ channel blocker lidocaine (5.0 mg/kg), their combination, or vehicle control. The left ventricle was processed for intracellular Na+ and Ca2+ m measurements.

RESULTS

limiting sarcolemmal Na+ entry attenuated cytosolic Na+ increase during VF/CC and the PR phase and prevented Ca2+ m overload yielding levels that corresponded to 77% and 71% of control hearts at VF/CC and PR, without differences among specific Na+ -limiting interventions. Limiting sarcolemmal Na+ entry attenuated reductions in left ventricular compliance during VF and prompted higher mean aortic pressure (110 +/- 7 vs. 95 +/- 11 mmHg, P < 0.001) and higher cardiac work index (159 +/- 34 vs. 126 +/- 29 g x m x min(-1) x kg(-1), P < 0.05) with lesser increases in circulating cardiac troponin I at 60 min PR.

CONCLUSIONS

Na+ -limiting interventions prevented excess Ca2+ m accumulation induced by ischemia and reperfusion and ameliorated myocardial injury and dysfunction.

Mitochondrial channelopathies in aging

Defects in ion channels (channelopathies) are increasingly found in a large spectrum of human pathologies including aging. Mutations in genes encoding ion channel proteins, which disrupt channel function, are the most commonly identified cause of channelopathies. Mutations in associated proteins, alterations in the expression of ion channels, or changes in the activity of non-mutated channel genes or associated proteins can also produce acquired channelopathies. Mitochondria, the powerhouse of the cells, are considered to be the most important cellular organelles to contribute to aging mainly because of their role in the production of reactive oxygen species in the initiation of apoptotic cell remodeling and in efficient ATP synthesis. During the past 50 years, multiple ion channels or transporters have been found in mitochondria, and the relationship between the activity of these channels and cellular aging, as well as the overall cellular biological function, has been intensively studied in a number of cell types and animal models. In this review, we discuss the better characterized mitochondrial ion channels whose dysfunction (mitochondrial channelopathies) may affect or accelerate the aging processes. These channels include the mitochondrial ATP-sensitive potassium channel (mitoK(ATP)), Ca(2+) transporters, voltage-dependent anion channel, and the mitochondrial permeability transition pore (mitoPTP).

Mitochondria, oxidative stress and aging

In the eighties, Miquel and Fleming suggested that mitochondria play a key role in cellular aging. Mitochondria, and specially mitochondrial DNA (mtDNA), are major targets of free radical attack. At present, it is well established that mitochondrial deficits accumulate upon aging due to oxidative damage. Thus, oxidative lesions to mtDNA accumulate with age in human and rodent tissues. Furthermore, levels of oxidative damage to mtDNA are several times higher than those of nuclear DNA. Mitochondrial size increases whereas mitochondrial membrane potential decreases with age in brain and liver. Recently, we have shown that treatment with certain antioxidants, such as sulphur-containing antioxidants, vitamins C and E or the Ginkgo biloba extract EGb 761, protects against the age-associated oxidative damage to mtDNA and oxidation of mitochondrial glutathione. Moreover, the extract EGb 761 also prevents changes in mitochondrial morphology and function associated with aging of the brain and liver. Thus, mitochondrial aging may be prevented by antioxidants. Furthermore, late onset administration of certain antioxidants is also able to prevent the impairment in physiological performance, particularly motor co-ordination, that occurs upon aging.

PUFA and aging modulate cardiac mitochondrial membrane lipid composition and Ca2+ activation of PDH

Aberrations in cell Ca2+ homeostasis have been known to parallel both changes in membrane lipid composition and aging. Previous work has shown that the lowered efficiency of work performance, which occurs in isolated hearts from rats fed a diet rich in n-6 polyunsaturated fatty acids (PUFA), relative to those fed n-3 PUFA, could be raised by mitochondrial (Mito) Ca2+ transport inhibition. We tested whether, after Ca2+-dependent stress, the Ca2+-dependent activation of pyruvate dehydrogenase (PDHA/PDHTotal) and Mito Ca2+ cycling could be manipulated by varying the ratio of n-3 to n-6 PUFA in Mito membranes in young (6 mo) and aged (24 mo) isolated rat hearts treated to n-3 or n-6 PUFA-rich diet. Inotropic stimulation by 1 microM norepinephrine (NE) of 24-mo n-6 PUFA-rich hearts elevated total Mito Ca2+ content 38% more than in 6-mo hearts (P < 0. 05). However, both the NE-induced rise in Mito Ca2+ and the difference in response between 6- and 24-mo hearts were partially abolished by n-3 PUFA treatment. NE increased the fractional activation of PDH by 44% above control levels in the 6-mo group compared with 49% in the 24-mo group after n-6 PUFA diet. However, NE stimulation of PDHA was attenuated by n-3 PUFA diet, attaining values only 29 and 23% above control levels in 6- and 24-mo mitochondria, respectively (P < 0.05). Global ischemia and reperfusion (I/R) in n-6 PUFA hearts gave rise to higher levels of total Mito Ca2+ concentration (P < 0.0001) and PDHA (P < 0.0001) compared with n-3 PUFA. Ruthenium red (3.4 microM) abolished the effects of I/R in all groups. With aging, heart Mito membrane phosphatidylcholine was increased after n-6 PUFA-rich diet (by approximately 15%, P < 0.05), whereas cardiolipin and n-3 PUFA content were diminished by 31% (P < 0.05) and 73% (P < 0.05), respectively. These effects were prevented by n-3 PUFA-rich diet. The present study, by directly manipulating the cardiac Mito membrane n-3-to-n-6 PUFA ratio, shows that the activation of Ca2+-dependent PDH can be augmented when the n-3-to-n-6 PUFA ratio is low (n-6 PUFA-rich diet; 24-mo hearts) or attenuated when this ratio is relatively high (n-3 PUFA-rich diet). We propose that one of the consequences of dietary-induced manipulation of membrane phospholipids and PUFAs may be the altered flux of Ca2+ across the Mito membrane and thus altered intramitochondrial Ca2+-dependent processes.

Congestive heart failure in the elderly

Several aspects of congestive heart failure are discussed in the light of international literature and of recent findings of our group. The annual incidence of heart failure in elderly subjects, aged >or=75y, is 13 to 50/1000, while it is 1.6/1000 in people aged 45-54 y. The prevalence of heart failure is about 3% in subjects aged 45-64% in subjects aged more than 65 y and 10% in subjects aged more than 75 y. These data are confirmed by our population based study in elderly subjects. The etiology of congestive heart failure is similar in elderly and middle-aged patients. However, several anatomo-functional, hormonal and autonomic nervous system changes, typical of congestive heart failure, occur during physiologic ageing processes also. These findings may explain the dramatic evolution of congestive heart failure in elderly patients. Moreover, some features of the elderly - e.g. comorbidity, atypical clinical presentations, loss of autonomy, increased iatrogen risk should be considered. No specific drugs exist for the pharmacologic treatment of heart failure in the elderly, so that the geriatric specificity in the treatment of heart failure can be recognized in the art of drug choice and dosage, to obtain the best results with the least side effects. The multiple etiology of congestive heart failure, the comorbidity, the loss of autonomy and the deterioration of cognitive functions suggest the need for multidimensional approach and continuative intervention in elderly patients with heart disease, and in particular with congestive heart failure. Further studies on disease- and age-related changes are necessary to develop new and more potent strategies to secure 'successful ageing'.

Role of calcium in brain aging

1. Calcium is a universal messenger of extracellular signals in a great variety of cells; it regulates several neuronal functions, such as neurotransmitter synthesis and release, neuronal excitability, phosphorylation and so on. Calcium is also involved in long-term processes, like memory. 2. Recent studies demonstrated that brain aging is characterized by alterations in neuronal function due to the changes in calcium homeostasis. This occurs for various reasons, such as changes in calcium channels, decrease of ion binding to specific proteins and changes in the mechanisms involved in its sequestration and extrusion from neuronal cell. 3. Moreover, it has been shown that high levels of glucocorticoids are neurotoxic, because they alter calcium homeostasis on hypothalamic neurons by increasing calcium voltage-dependent flow, especially in aged neurons. 4. New information about the role of calcium in brain aging could derive from the expansion of new imaging techniques, such as positron emission tomography, single photon emission tomography and nuclear magnetic resonance, which allow in vivo quantitative measurements of functional parameters and their comparison with behavioural data.

Human epidermal cells progressively lose their cardiolipins during ageing without change in mitochondrial transmembrane potential

Mitochondria dysfunction is considered to be a major cause of the modifications that occur during cell ageing. For this reason, cardiolipin, a suitable marker of the chondriome, as well as the mitochondrial transmembrane potential were examined in keratinocytes obtained from 9- to 75-year-old women. The study was carried out by flow cytometry using two fluorescent mitochondria probes: nonyl acridine orange, which binds specifically to cardiolipin, and rhodamine 123, which is incorporated mainly in response to transmembrane potential. Cardiolipin levels in cells from elderly donors (75 years old) would be 57% lower (r = 0.540; P = 0.0002) than those in children (9 years old), while the inner transmembrane potential remained unchanged (r = 0.0394; P = 0.8017). The stability of the membrane potential may be explained by either or both of the following hypotheses: (i) the same pool of organelles able to maintain membrane potential is conserved even when cardiolipin levels decrease (ii) mitochondria membrane potential does indeed decrease with age but is compensated by glycolysis energy production. Finally, it may be stated that the fluorescent probes nonyl acridine orange and rhodamine 123 might be of interest in testing the phenotype of senescent cells and would be useful in screening the role of certain specific genes in cell ageing.

Impairment of mitochondrial oxidative phosphorylation in the brain of aged mice

To elucidate the role of mitochondrial oxidative phosphorylation in neuronal aging, we have studied the activity of the respiratory complexes in the brain of young, adult and old mice. In synaptic mitochondria, we found a significant decrease in complexes IV (29%, P < 0.001) and V (21%, P < 0.01) in old as compared with adult mice. Nonsynaptic mitochondria also showed a senescent decrease in complexes I (15%, P < 0.01), II + III (34%, P < 0.01) and IV (17%, P < 0.01) activities. These findings suggest a dysfunction in mitochondrial oxidative phosphorylation in brain aging.

Loss of paired-pulse facilitation at the corticostriatal synapse of the aged rat

Changes in calcium (Ca2+) homeostasis have been proposed to contribute to the aging process. Paired-pulse facilitation, a form of synaptic enhancement that relies upon an accumulation of Ca2+ in the presynaptic terminal, was used to examine the effect of aging at the corticostriatal synapse. Intracellular recordings in striatal neurons from young rats demonstrated a consistent enhancement in the second of two synaptic responses evoked by stimulation of the corpus callosum. In contrast, neurons from aged rats showed a consistent depression of the second synaptic response at identical pairing intervals. These differences were not explained by an age-dependent increase in synaptic depression and demonstrate an alteration in the Ca(2+)-mediated process of presynaptic facilitation.

Age-related changes in the sensitivity of sympathetic nerves to altered extracellular calcium in tail arteries of F-344 rats

There is a significant age-related increase in stimulation evoked norepinephrine release from adrenergic nerves in tail arteries of F-344 rats, that is not accounted for by a change in function of prejunctional alpha 2-adrenergic receptors. To further explore the mechanism of this age-related change in transmitter release, we investigated the effect of altered extracellular calcium. With short stimulation trains the effects of altered extracellular calcium were significantly greater in 20-month-old tail arteries compared to 6 months. At the highest calcium concentration (7.5 mM) when alpha 2-adrenergic receptors were active or blocked, there was a significant decline in fractional norepinephrine release only in arteries of 20-month-old animals. With long stimulation trains the effects of altered extracellular calcium were not as pronounced as with short trains, but the effect of calcium was still significantly greater in 20 month old tail arteries. With alpha 2-adrenergic receptors blocked 6 month tail arteries were insensitive to altered calcium while 20-month tail arteries remained sensitive. One explanation for these findings may be an age-related change in the efficiency of intracellular calcium buffering mechanisms leading to greater calcium transients in the nerves of older animals.

Effect of aging on the activity of the phosphate carrier and on the lipid composition in rat liver mitochondria

The effect of aging on the activity of the phosphate carrier and on the lipid composition in rat liver mitochondria has been investigated. It was found that the rate of phosphate transport in mitochondria from aged rats (28 months old) is significantly reduced (around 40%) compared to that obtained in mitochondria from young control rats (5 months old). Kinetic analysis of the phosphate transport indicates that only the Vmax of this process is affected, while there is no change in the Km values. The lower activity of the phosphate carrier in mitochondria from aged rats is also documented by swelling experiments. The age-related decrement in the activity of the phosphate carrier was found not to be due neither to a change in the endogenous content of phosphate nor to a change in the transmembrane delta pH value. Inhibitor titrations with mersalyl provide no evidence for a lower content of functional phosphate translocase in mitochondria from aged rats. There is no difference either in the respiratory control ratios or in the ADP/O ratios between mitochondria from young and aged animals. The hepatic mitochondrial lipid composition is altered significantly in aged rats: the total cholesterol increases (31%), the phospholipids decrease (12%), and the cholesterol/phospholipid molar ratio increases (44%). Among the phospholipids cardiolipin shows the greatest alteration (30% decrease with age). Alterations were also found in the pattern of fatty acids. The age-related decrement in the activity of the phosphate carrier appears to be dependent on changes in the lipid domain surrounding the carrier protein molecule in the mitochondrial membrane.

Age-related changes in the activity of the pyruvate carrier and in the lipid composition in rat-heart mitochondria

The effect of aging on the activity of the pyruvate translocator and on the lipid composition in rat-heart mitochondria has been investigated. It has been found that the rate of pyruvate transport in mitochondria from aged rats (28 months old) is markedly reduced (38%) as compared with that obtained with mitochondria from young adults rats (4 months old). Kinetic analysis of the pyruvate transport shows that only the Vmax of this process is decreased, while there is no change in the Km values. The age-related decrement in the activity of the pyruvate carrier is not due to a decrease in the transmembrane delta pH value, neither does it depend on a decrease in the total number of the pyruvate carrier molecules, titrated with radioactive alpha-cyanocinnamate. The lower activity of the pyruvate translocator in mitochondria from aged rats is associated to a parallel decrement of the rate of pyruvate-dependent oxygen uptake. There is, however no appreciable difference in either the respiratory control ratios or in the ADP/O ratios between these two types of mitochondrion. The Arrhenius plot characteristics differ for pyruvate transport activity in mitochondria from aged rats as compared with young rats in that the break point of the biphasic plot is shifted to a higher temperature. The heart mitochondrial lipid composition is significantly altered in aged rats. The total cholesterol increases (43%), the phospholipids decrease (15%) and the cholesterol/phospholipid molar ratio increases (68%). Among phospholipids, cardiolipin shows the greatest alteration (28% decrease in aged rats). The lower activity of the pyruvate carrier in mitochondria from aged rats may be ascribed to changes in the lipid domain surrounding the carrier molecule in the membrane.

The role of calcium regulation in brain aging: reexamination of a hypothesis

Studies of the central nervous system have a long history; however, it is only recently that we have begun to understand brain function in health and disease states. And, the topic of the aging brain has become a subject of intense study for a short period. At present, the process of normal aging is relatively poorly understood. Although there are a number of theories of aging, no single theory appears to account for most age-dependent brain changes. This review provides a re-evaluation of the "Calcium Hypothesis of Brain Aging" in light of new evidence which supports the proposition that cellular mechanisms, which maintain the homeostasis of cytosol Ca2+ concentration, play a key role in brain aging; and that sustained changes in [Ca2+]i homeostasis provide the final common pathway for age-associated brain changes. This revision of the calcium hypothesis suggests that there is a complex interaction between the amount of [Ca2+]i perturbation and the duration of such deregulation of Ca2+ homeostasis and it proposes that a small disturbance in Ca2+ homeostasis with a sustained increase in [Ca+]i over a long period has similar cell injuring consequences as that produced by a large increase in [Ca2+]i over a shorter period. Although there are several alternative mechanisms through which the regulation of cytosol [Ca2+]i can be disrupted (such as changes in ion channels, extrusion pumps, and sequestration), this review focuses on disruptions in energy metabolism and changes in the structure and function of membranes as the most likely antecedent events which lead to disruption of Ca2+ homeostasis. The principle purpose of this review is to identify scientific opportunities and stimulate further research into cellular mechanisms of brain aging.

Age-related changes in respiration coupled to phosphorylation. II. Cardiac mitochondria

Age-related changes in mitochondrial adenine nucleotide metabolism may underlie the progressive decline in cardiac function. Oxidase activity coupled with phosphorylation, adenine nucleotide translocase (AdNT) activity, adenine nucleotide pool size and membrane lipid composition were determined using cardiac mitochondria from young (3 months), mature (12 months) and aged (24 months) Fischer 344 male rats which had been fed NIH-31 diet. While an age-associated 15% decrease in respiratory activity was not significant, AdNT activity of the aged rat was 20% lower (P less than 0.05) than that of the young rat. The exchangeable matrix adenine nucleotide pool (ATP + ADP) tended to decrease with age. In comparison to the young, membrane lipids of cardiac mitochondria from aged rat had a 43% higher (P less than 0.01) cholesterol/phospholipid-Pi ratio and a significantly lower (P less than 0.01) phosphatidyl ethanolamine/phosphatidyl choline ratio. The overall change in the fatty acid pattern of mitochondrial membrane lipids resulted in a significant (P less than 0.01) decrease in the n-6/n-3 fatty acid ratio. All values obtained for the mature rat fell between those of the young and aged rats. These data suggest that the reduced cardiac AdNT activity in the aged rat is a consequence of both a diminished pool of exchangeable adenine nucleotides and a lower AdNT velocity. Age-related changes in the lipid components of the membrane matrix in which the AdNT is embedded may underlie the decrease in respiratory activity.

Intracellular calcium, insulin secretion, and action

Changes in cytosolic free calcium concentration [( Ca2+]i) constitute an important element of signal transduction in various cells. These changes either reflect alterations in calcium (Ca2+) fluxes or result from mobilization of intracellular Ca2+ stores. In pancreatic islet cells, an increase in [Ca2+]i is critical for secretagogue-induced insulin release. Thus, glucose evokes a rapid increase in [Ca2+]i, primarily by stimulating Ca2+ influx. Under physiologic conditions, glucose may also promote mobilization of intracellular Ca2+ stores by virtue of stimulating membrane phospholipid hydrolysis and formation of inositol triphosphate, a potent stimulus for Ca2+ mobilization. This action of glucose requires the presence of extracellular Ca2+. The magnitude of change in [Ca2+]i may not parallel the level of insulin release, suggesting that the role of [Ca2+]i in the process of insulin release must be considered in concert with other cellular mechanisms. The role of [Ca2+]i in promoting insulin action is a subject of continuous controversy. Recent observations that chelation of intracellular Ca2+ with quin-2 diminishes insulin action (and that of insulin mimetics) support the role of Ca2+ in mediating the insulin-generated signal. Insulin has also been demonstrated to increase [Ca2+]i in adipocytes in close association with its effect on 2-deoxyglucose uptake. Finally, in both pancreatic islet cells and adipocytes, high concentrations of either extracellular or intracellular Ca2+ inhibit cellular responsiveness. The optimal concentrations of cytosolic Ca2+ appear to be within the 140 to 350 nM range. When Ca2+ concentrations are too low or too high, the ability of pancreatic islets and insulin target cells to respond appropriately to physiologic stimuli is significantly diminished. Impaired cellular Ca2+ homeostasis (either primary or secondary to other cellular lesions) may represent a crucial and identical link in the pathogenesis of impaired insulin secretion and in the pathogenesis of impaired insulin action.

Changes of mitochondrial membrane proteins in rat cerebellum during aging

Qualitative and quantitative changes of mitochondrial membrane proteins during aging were investigated. Free (non-synaptic) mitochondria were purified from rat cerebellum at different ages (4, 8, 12, 16, 20, and 24 months). Mitochondrial outer membrane (OM), inner membrane (IM) and matrix (MX) were separated and the proteins were extracted and analyzed by gel-electrophoresis. After staining, the gels were scanned densitometrically to quantify the proteins. No significant changes in the quantity of OM or MX protein subunits were observed, while several statistically significant quantitative changes in IM proteins with age were found. These age-dependent modifications of inner membrane mitochondrial proteins may play an important role in energy transduction, transport systems and regulatory enzymatic activities in mitochondria.

Mechanisms of altered hormone and neurotransmitter action during aging: the role of impaired calcium mobilization

Age-related changes in hormone and neurotransmitter regulation of physiological functions result from various mechanistic alterations. In many cases changes in the receptors for these agents appear to be closely linked to altered responsiveness. In other instances, receptors are unaffected by aging, and various post-receptor changes result in functional deterioration. Examples of the latter situation include stimulation of cyclic AMP production and high-affinity association of steroid receptor-hormone complexes with nuclear acceptor sites in various cell and tissue types. One of the most noteworthy post-receptor changes appears to be an impaired ability to stimulate calcium mobilization in many aged systems resulting in reductions in various biological responses. Although the processes which govern regulation of calcium fluxes vary with cell type, many such dysfunctions can be at least partially reversed if sufficient calcium can be transported to appropriate cellular sites. Thus, elucidation of the molecular mechanisms involved in impaired calcium mobilization may provide the basis for new therapeutic strategies.

Enzyme histochemistry of the choroid plexus in old rats

The influence of ageing on the metabolic profile of lateral ventricle choroid plexus epithelial cells from young (3-month-old) and aged (26-month-old) male Wistar rats was studied using enzyme histochemical techniques. The following enzymatic activities related to energy transduction were examined: lactate-(LDH) and succinate- (SDH) dehydrogenases; NADH2-tetrazolium reductase (NADHD) and alpha-glycerophosphate-dehydrogenase (GPDH). The intensity of enzymatic staining within single choroid plexus epithelial cells from young and old animals was assessed microphotometrically. In the choroid plexus epithelial cells of young rats NADHD was the enzymatic activity more heavily stained; cell levels of LHD and GPDH were approximately the same and SDH reactivity was less intense. In old age LDH was reduced by 9.3%, SDH was reduced by 26.1%, NADHD was reduced by 8.6% and GPDH was reduced by 3.6%. The possibility that impaired energy transduction mechanisms at the level of choroid plexus epithelium in old age may influence functional activity of the choroid plexus is discussed.

Lack of age-dependent changes in rat heart mitochondria

The effects of aging on the composition and function of cardiac mitochondria from rats exhibiting significant decreases in synaptic brain mitochondria composition and function have been studied. Cytochrome content and cytochrome absorbance wavelength maxima do not change in heart mitochondria. Respiratory activities, respiratory control ratios, ADP/O ratios, and H+/O ratios do not change with increasing age. Unlike in brain synaptic tissue, energy output of the heart does not decrease with age.

Calcium and the aging nervous system

Many aspects of calcium homeostasis change with aging. Numerous calcium compartments complicate studies of altered calcium regulation. However, age-related decreases in calcium permeation across membranes and mobilization from organelles may be a common fundamental change. Deficits in ion movements appear to lead to altered coupling of calcium-dependent biochemical and neurophysiological processes and may lead to pathological and behavioral changes. The calcium-associated changes during aging probably do not occur with equal intensity in all cell types or in different parts of the same cell. Thus, cells or compartments with a high proportion of calcium activated processes would be more sensitive to diminished calcium availability. These age-related changes may predispose the brain to the development of age-related neurological disorders. The effects of decreased ion movement may be further aggravated by an age-related decline in other calcium-dependent processes. Depression of some of these calcium-dependent functions appears physiologically significant, since increasing calcium availability ameliorates age-related deficits in neurotransmission and behavior. A better understanding of the interactions between calcium homeostasis and calcium-dependent processes during aging will likely help in the design of more effective therapeutic strategies.

Polyamines stimulate mitochondrial calcium transport in rat brain

The effects of the polyamines spermine and spermidine on rat brain mitochondrial calcium transport were examined using a variety of techniques for measuring the kinetics of calcium uptake and the buffering capabilities of isolated mitochondria. Spermine both increased the rate of calcium accumulation and decreased the set-point to which isolated mitochondria buffer free calcium concentration. In the presence of physiological concentrations of sodium and magnesium, spermine lowered the extramitochondrial calcium level to approximately 0.3 microM, a value close to the resting intracellular calcium concentration. The effect of polyamines was concentration dependent, with a half-maximal effect of spermine observed at approximately 0.1-0.4 mM (respiratory substrate dependent), whereas spermidine was approximately 10 times less potent. Calcium transport by hippocampal mitochondria was stimulated markedly more by spermine than was calcium transport by mitochondria isolated from brainstem. The stimulatory effect of spermine was not due to an increase in the transport of respiratory substrates inside the mitochondria nor to an effect on the enzymes using these respiratory substrates. An examination of the effect of spermine on the kinetics of calcium uptake indicated that spermine increased calcium uptake maximally at low calcium concentrations. Beyond that level, the stimulatory effect of spermine decreases, and spermine can even inhibit calcium uptake. These results are in good agreement with previous reports on the effects of polyamines on calcium transport in mitochondria from peripheral tissue. They support the hypothesis that spermine increases the rate of calcium uptake by mitochondria by increasing the affinity of the uniporter for calcium.(ABSTRACT TRUNCATED AT 250 WORDS)

The influence of age on the calcium-efflux pathway and matrix calcium buffering power in brain mitochondria

The variations with age of the ruthenium red-insensitive calcium efflux rate have been studied in rat brain mitochondria. Both H+- and Na+-dependent effluxes are decreased with age when expressed as a function of calcium taken up in mitochondria incubated in the presence of 0.8 mM inorganic phosphate (Pi) and 0.2 mM ADP. However, the age-dependent differences in calcium efflux rates disappear when mitochondria are incubated in the absence of ADP and Pi. It is suggested that the decrease in efflux rate observed with age corresponds to an increased calcium buffering power of the mitochondrial matrix due to an increase in mitochondrial Pi. The causes of the increased Pi accumulation in old-rat-brain mitochondria are yet unknown but possibly not due to differences in the Pi efflux. The results suggest that the age-dependent lowering of the free calcium concentration in the brain mitochondrial matrix together with the reduced activity of the calcium uniporter (Vitórica, J. and Satrústegui, J. (1986) Brain Research 378, 36-48) could lead to an impaired activation of mitochondrial dehydrogenases after a rise in cytosolic calcium.

Involvement of mitochondria in the age-dependent decrease in calcium uptake of rat brain synaptosomes

Calcium uptake in rat brain synaptosomes decreases during ageing. The possible involvement of mitochondria in altered calcium homeostasis has been investigated. Mitochondria isolated from old rat brain showed decreased calcium uptake rates. Since neither the mitochondrial membrane potential nor the delta pCa decreases with age, it was concluded that variations in the driving force for calcium uptake were not the cause for impaired calcium transport in mitochondria from aged rat brain. The steady state calcium distribution in isolated aged rat brain mitochondria was achieved at higher extramitochondrial calcium concentrations than that of adults. Studying the effects of the selective release of calcium from the mitochondrial pool by the addition of an uncoupler to 45Ca loaded synaptosomes incubated in high-potassium media, it was found that the intrasynaptic mitochondrial pool and the intra/extramitochondrial 45Ca distribution also decreased considerably in 24-month-old rats. Steady state fluorescence anisotropy (rs) of diphenylhexatriene-labelled mitoplasts from 'free' brain mitochondria increased with ageing. However, since no changes in rs from synaptosomal mitochondria were found in 24-month-old rats, it is suggested that alterations in lipid dynamics are not involved in the impaired calcium uptake observed in brain mitochondria from aged rats. The implications of these findings in the calcium homeostasis of brain endings are discussed.

Reduced calcium uptake by rat brain mitochondria and synaptosomes in response to aging

Synaptosomes were isolated from cerebral cortex of 3-, 18- and 24-month-old male, Fisher 344 rats and 45Ca2+ uptake was measured at 1, 3, 5, 15 and 30 s time periods following 65 mM KCl depolarization. Identical experiments were performed in which 5 mM KCl was added to examine age-related changes in resting 45Ca2+ accumulation by synaptosomes. Both 'fast-' and 'slow-phase' voltage-dependent 45Ca2+ uptake were significantly reduced in synaptosomes from 18- and 24- vs 3-month-old rats. No age-related change in resting (5 mM KCl) 45Ca2+ accumulation was observed. ATP-dependent and respiration-linked 45Ca2+ uptake was examined in mitochondria isolated from whole brains of 3- and 28-month-old male, hooded Long-Evans rats. Both ATP-dependent and glutamate-malate-ADP stimulated 45Ca2+ uptake by mitochondria were markedly reduced in response to aging. Respiratory control ratios were the same for 3- and 28-month-old mitochondria, suggesting that the decrement in 45Ca2+ uptake was not caused by an age-related decline in respiratory activity of mitochondria. The results of this study show that both voltage-dependent calcium entry into presynaptic nerve terminals and calcium uptake by mitochondria in brain decline with advanced aging. Age-related changes in cytosolic calcium levels could underlie, at least in part, cellular decrements in brain observed with aging.