Emergence of early alterations in network oscillations and functional connectivity in a tau seeding mouse model of Alzheimer's disease pathology.

Synaptic dysfunction and disconnectivity are core deficits in Alzheimer's disease (AD), preceding clear changes in histopathology and cognitive functioning. Here, the early and late effects of tau pathology induction on functional network connectivity were investigated in P301L mice. Multichannel EEG oscillations were used to compute (1) coherent activity between the prefrontal cortex (PFC) and hippocampus (HPC) CA1-CA3 networks; (2) phase-amplitude cross frequency coupling (PAC) between theta and gamma oscillations, which is instrumental in adequate cognitive functioning; (3) information processing as assessed by auditory evoked potentials and oscillations in the passive oddball mismatch negativity-like (MMN) paradigm. At the end, the density of tau aggregation and GABA parvalbumin (PV+) interneurons were quantified by immunohistochemistry. Early weakening of EEG theta oscillations and coherent activity were revealed between the PFC and HPC CA1 and drastic impairments in theta-gamma oscillations PAC from week 2 onwards, while PV+ interneurons count was not altered. Moreover, the tau pathology disrupted the MMN complex amplitude and evoked gamma oscillations to standard and deviant stimuli suggesting altered memory formation and recall. The induction of intracellular tau aggregation by tau seed injection results in early altered connectivity and strong theta-gamma oscillations uncoupling, which may be exploited as an early electrophysiological signature of dysfunctional neuronal networks.

Translational neurophysiological markers for activity of the metabotropic glutamate receptor (mGluR2) modulator JNJ-40411813: Sleep EEG correlates in rodents and healthy men.

Alterations in rapid eye movement sleep (REM) have been suggested as valid translational efficacy markers: activation of the metabotropic glutamate receptor 2 (mGluR2) was shown to increase REM latency and to decrease REM duration. The present paper addresses the effects on vigilance states of the mGluR2 positive allosteric modulator (PAM) JNJ-40411813 at different circadian times in rats and after afternoon dosing in humans. Due to its dual mGluR2 PAM/serotonin 2A (5-HT2A) receptor antagonism in rodents, mGlu2R specificity of effects was studied in wild-type (WT) and mGluR2 (-/-) mice. 5-HT2A receptor occupancy was determined in humans using positron emission tomography (PET). Tolerance development was examined in rats after chronic dosing. EEG oscillations and network connectivity were assessed using multi-channel EEG. In rats, JNJ-40411813 increased deep sleep time and latency of REM onset but reduced REM time when administered 2 h after 'lights on' (CT2): this was sustained after chronic dosing. At CT5 similar effects were elicited, at CT10 only deep sleep was enhanced. Withdrawal resulted in baseline values, while re-administration reinstated drug effects. Parieto-occipital cortical slow theta and gamma oscillations were correlated with low locomotion. The specificity of functional response was confirmed in WT but not mGluR2 (-/-) mice. A double-blind, placebo-controlled polysomnographic study in healthy, elderly subjects showed that 500 mg of JNJ-40411813 consistently increased deep sleep time, but had no effect on REM parameters. This deep sleep effect was not explained by 5-HT2A receptor binding, as in the PET study even 700 mg only marginally displaced the tracer. JNJ-40411813 elicited comparable functional responses in rodents and men if circadian time of dosing was taken into account. These findings underscore the translational potential of sleep mechanisms in evaluating mGluR2 therapeutics when administered at the appropriate circadian time.

Relevance of the metabotropic glutamate receptor (mGluR5) in the regulation of NREM-REM sleep cycle and homeostasis: evidence from mGluR5 (-/-) mice.

Sleep is a homeostatically regulated behavior and sleep loss evokes a proportional increase in sleep time and delta slow wave activity. Glutamate and pharmacological modulation of the metabotropic glutamate receptors (mGluR) signaling have been implicated in the organization of vigilance states. Here, the role of the mGluR5 on homeostatic regulation of sleep-wake cycle and electroencephalographic (EEG) activity was examined in mGluR5 (-/-) mice. We first characterized the sleep-wake EEG phenotype in mGluR5 (-/-) and wild-type (WT) littermates mice by continuous recording for 72h of EEG, body temperature (BT) and locomotor activity (LMA). Next, we investigated the influence of sleep deprivation on the recovery sleep and EEG slow wave activity (1-4Hz) during NREM sleep to assess whether mGluR5 deletion affects the sleep homeostasis process. Like the control animals, mGluR5 (-/-) mice exhibited a clear-cut circadian sleep-wake architecture, however they showed reduced REM sleep time during the light phase with shorter REM sleep bouts and reduced state transitions in the NREM sleep-REM sleep cycle during the first and last 24h of the spontaneous 72h recording period. In addition, mGluR5 (-/-) mice had decreased slow EEG delta power during NREM sleep and enhanced LMA associated with elevated BT during the dark phase. Moreover, mGluR5 (-/-) mice exhibited reduced slow wave activity and sleep drive after sleep deprivation, indicating altered sleep homeostatic processes. The findings strongly indicate that mGluR5 is involved in shaping the stability of NREM sleep-REM sleep state transitions, NREM slow wave activity and homeostatic response to sleep loss.

Diseases involving the Golgi calcium pump.

Secretory-pathway Ca2(+)-transport ATPases (SPCA) provide the Golgi apparatus with Ca2+ and Mn2+ needed for the normal functioning of this organelle. Loss of one functional copy of the human SPCA1 gene (ATP2C1) causes Hailey-Hailey disease, a rare skin disorder characterized by recurrent blisters and erosions in the flexural areas. Here, we will review the properties and functional role of the SPCAs. The relationship between Hailey-Hailey disease and its defective gene (ATP2C1) will be adressed as well.

New perspectives on the role of SERCA2's Ca2+ affinity in cardiac function.

Cardiomyocyte relaxation and contraction are tightly controlled by the activity of the cardiac sarco(endo)plasmic reticulum (SR) Ca2+ transport ATPase (SERCA2a). The SR Ca2+ -uptake activity not only determines the speed of Ca(2+) removal during relaxation, but also the SR Ca2+ content and therefore the amount of Ca2+ released for cardiomyocyte contraction. The Ca2+ affinity is the major determinant of the pump's activity in the physiological Ca2+ concentration range. In the heart, the affinity of the pump for Ca2+ needs to be controlled between narrow borders, since an imbalanced affinity may evoke hypertrophic cardiomyopathy. Several small proteins (phospholamban, sarcolipin) adjust the Ca2+ affinity of the pump to the physiological needs of the cardiomyocyte. It is generally accepted that a chronically reduced Ca2+ affinity of the pump contributes to depressed SR Ca2+ handling in heart failure. Moreover, a persistently lower Ca2+ affinity is sufficient to impair cardiomyocyte SR Ca2+ handling and contractility inducing dilated cardiomyopathy in mice and humans. Conversely, the expression of SERCA2a, a pump with a lower Ca2+ affinity than the housekeeping isoform SERCA2b, is crucial to maintain normal cardiac function and growth. Novel findings demonstrated that a chronically increased Ca2+ affinity also may trigger cardiac hypertrophy in mice and humans. In addition, recent studies suggest that some models of heart failure are marked by a higher affinity of the pump for Ca2+, and hence by improved cardiomyocyte relaxation and contraction. Depressed cardiomyocyte SR Ca2+ uptake activity may therefore not be a universal hallmark of heart failure.

Cytosolic Ca2+ signals depending on the functional state of the Golgi in HeLa cells.

The Golgi apparatus is, like the endoplasmic reticulum, an inositol-1,4,5-trisphosphate-sensitive Ca2+ store, but its role in setting up Ca2+ signals is not well understood. We have now measured histamine-induced Ca2+ signals in HeLa cells pretreated with brefeldin A, a fungal metabolite that leads to the fragmentation and subsequent disappearance of the Golgi apparatus by its reabsorption within the endoplasmic reticulum. Ca2+ responses in which the free cytoplasmic Ca2+ concentration returned to resting levels during the histamine stimulation (mainly baseline Ca2+ oscillations or a single Ca2+ peak) occurred more often in brefeldin A pretreated cells, resulting in a lower Ca2+ plateau in population measurements. The latencies before the onset of the Ca2+ signals were longer after brefeldin A pretreatment. These results suggest that the integrity of the Golgi apparatus contributes to the shaping of intracellular Ca2+ signals.

Calcium release from the Golgi apparatus and the endoplasmic reticulum in HeLa cells stably expressing targeted aequorin to these compartments.

Extracellular agonists mobilize Ca2+ from SERCA-comprising intracellular Ca2+ stores located in both the Golgi apparatus and the endoplasmic reticulum. Ca2+ release from both these compartments was studied in HeLa cells stably expressing the luminescent Ca2+ indicator aequorin specifically targeted to these compartments. Changes in lumenal [Ca2+] as detected by the aequorin measurements were correlated with parallel changes in total Ca2+ content of the stores. The latencies and initial rates of Ca2+ release from the Golgi apparatus and the endoplasmic reticulum were quite similar. However, maximal Ca2+ release measured with Golgi-targeted aequorin terminated faster than that from the endoplasmic reticulum. The rate and extent of Ca2+ depletion from both compartments correlated well with the peak amplitude of the cytosolic [Ca2+] rise. Time-course experiments further revealed that the peak of the cytosolic Ca2+ response occurred before the lumenal [Ca2+] reached its lowest level. We conclude that both the Golgi apparatus and the endoplasmic reticulum contribute to the rise in cytosolic [Ca2+] upon agonist stimulation, but the kinetics of the Ca2+ release are different.

Inositol trisphosphate producing agonists do not mobilize the thapsigargin-insensitive part of the endoplasmic-reticulum and Golgi Ca2+ store.

Non-mitochondrial intracellular Ca2+ stores contain both thapsigargin-sensitive sarco(endo)plasmic-reticulum Ca2+-ATPases (SERCA) and thapsigargin-insensitive secretory-pathway Ca2+-ATPases (SPCA1). We now have studied the Ca2+-release properties of the compartments associated with these pumps in intact, i.e. non-permeabilized, cells of different origin (HeLa, keratinocytes, 16HBE14o-, COS-1, A7r5) and with different approaches (45Ca2+ fluxes, Ca2+ imaging and measurements of the free luminal [Ca2+] in the endoplasmic-reticulum and the Golgi apparatus using targeted aequorin). Application of an extracellular agonist in the absence of thapsigargin induced in all cells a Ca2+ release from both the endoplasmic-reticulum and the Golgi apparatus. The agonists were not able to release Ca2+ in the presence of 10 microM thapsigargin, except in COS-1 cells overexpressing SPCA1, where this pump not only appeared in the Golgi compartment but also overflowed into the agonist-sensitive part of the endoplasmic-reticulum. We conclude that the subcompartments of the endoplasmic-reticulum and of the Golgi complex that endogenously express SPCA1 are insensitive to agonist stimulation.

Action potential changes associated with a slowed inactivation of cardiac voltage-gated sodium channels by KB130015.

1. We have studied the acute cardiac electrophysiological effects of KB130015 (KB), a drug structurally related to amiodarone. Membrane currents and action potentials were measured at room temperature or at 37 degrees C during whole-cell patch-clamp recording in ventricular myocytes. Action potentials were also measured at 37 degrees C in multicellular ventricular preparations. 2. The effects of KB were compared with those of anemone toxin II (ATX-II). Both KB and ATX-II slowed the inactivation of the voltage-gated Na(+) current (I(Na)). While KB shifted the steady-state voltage-dependent inactivation to more negative potentials, ATX-II shifted it to more positive potentials. In addition, while inactivation proceeded to completion with KB, a noninactivating current was induced by ATX-II. 3. KB had no effect on I(K1) but decreased I(Ca-L) The drug also did not change I(to) in mouse myocytes. 4. The action potential duration (APD) in pig myocytes or multicellular preparations was not prolonged but often shortened by KB, while marked APD prolongation was obtained with ATX-II. Short APDs in mouse were markedly prolonged by KB, which frequently induced early afterdepolarizations. 5. A computer simulation confirmed that long action potentials with high plateau are relatively less sensitive to a mere slowing of I(Na) inactivation, not associated with a persisting, noninactivating current. In contrast, simulated short action potentials with marked phase-1 repolarization were markedly modified by slowing I(Na) inactivation. 6 It is suggested that a prolongation of short action potentials by drugs or mutations that only slow I(Na) inactivation does not necessarily imply identical changes in other species or in different myocardial regions.

Similar Ca(2+)-signaling properties in keratinocytes and in COS-1 cells overexpressing the secretory-pathway Ca(2+)-ATPase SPCA1.

Mutations in the ubiquitously expressed secretory-pathway Ca(2+)-ATPase (SPCA1) Ca(2+) pump result in Hailey-Hailey disease, which almost exclusively affects the epidermal part of the skin. We have studied Ca(2+) signaling in human keratinocytes by measuring the free Ca(2+) concentration in the cytoplasm and in the lumen of both the Golgi apparatus and the endoplasmic reticulum. These signals were compared with those recorded in SPCA1-overexpressing and control COS-1 cells. Both the sarco(endo)plasmic-reticulum Ca(2+)-ATPase (SERCA) and SPCA1 can mediate Ca(2+) uptake into the Golgi stacks. Our results indicate that keratinocytes mainly used the SPCA1 Ca(2+) pump to load the Golgi complex with Ca(2+) whereas the SERCA Ca(2+) pump was mainly used in control COS-1 cells. Cytosolic Ca(2+) signals in keratinocytes induced by extracellular ATP or capacitative Ca(2+) entry were characterized by an unusually long latency reflecting extra Ca(2+) buffering by an SPCA1-containing Ca(2+) store, similarly as in SPCA1-overexpressing COS-1 cells. Removal of extracellular Ca(2+) elicited spontaneous cytosolic Ca(2+) transients in keratinocytes, similarly as in SPCA1-overexpressing COS-1 cells. With respect to Ca(2+) signaling keratinocytes and SPCA1-overexpressing COS-1 cells therefore behaved similarly but differed from control COS-1 cells. The relatively large contribution of the SPCA1 pumps for loading the Golgi stores with Ca(2+) in keratinocytes may, at least partially, explain why mutations in the SPCA1 gene preferentially affect the skin in Hailey-Hailey patients.

Dynamics of Boolean networks controlled by biologically meaningful functions.

The remarkably stable dynamics displayed by randomly constructed Boolean networks is one of the most striking examples of the spontaneous emergence of self-organization in model systems composed of many interacting elements (Kauffman, S., J. theor. Biol.22, 437-467, 1969; The Origins of Order, Oxford University Press, Oxford, 1993). The dynamics of such networks is most stable for a connectivity of two inputs per element, and decreases dramatically with increasing number of connections. Whereas the simplicity of this model system allows the tracing of the dynamical trajectories, it leaves out many features of real biological connections. For instance, the dynamics has been studied in detail only for networks constructed by allowing all theoretically possible Boolean rules, whereas only a subset of them make sense in the material world. This paper analyses the effect on the dynamics of using only Boolean functions which are meaningful in a biological sense. This analysis is particularly relevant for nets with more than two inputs per element because biological networks generally appear to be more extensively interconnected. Sets of the meaningful functions were assembled for up to four inputs per element. The use of these rules results in a smaller number of distinct attractors which have a shorter length, with relatively little sensitivity to the size of the network and to the number of inputs per element. Forcing away the activator/inhibitor ratio from the expected value of 50% further enhances the stability. This effect is more pronounced for networks consisting of a majority of activators than for networks with a corresponding majority of inhibitors, indicating that the former allow the evolution of larger genetic networks. The data further support the idea of the usefulness of logical networks as a conceptual framework for the understanding of real-world phenomena.

Ion transport systems as targets of free radicals during ischemia reperfusion injury.

Oxidative stress is a recognized pathogenic factor in ischemia/reperfusion injury (IRI). Iron induced generation of reactive oxygen species (ROS) in vitro reduces both the Na+K+-ATPase activity and Na+-Ca2+ exchanger of synaptosomal membranes, concomitantly with alteration of physical state of membranes. Oxidative insult also leads to the loss of ability of endoplasmic reticular membranes (ER) to sequester Ca2+ as well as to the increase of Ca2+ permeability. Furthermore, ROS induces both lipid peroxidation and lipid-independent modifications of membrane proteins. Acute in vivo ischemia alters kinetic parameters of Na+K+-ATPase affecting mainly the dephosphorylation step of ATPase cycle with parallel changes of Na+-Ca2+ exchanger and alterations of physical membrane environment. Subsequent reperfusion after ischemia is associated with decrease of immuno signal for PMCA 1 isoform in hippocampus. In addition, incubation of non-ischemic membranes with cytosol from ischemic hippocampus decreases level of PMCA 1 in non-ischemic tissues. Loss of PMCA 1 protein is partially protected both by calpain- and by non-specific protease inhibitors which suggest possible activation of proteases in the reperfusion period. On the other hand, ischemia does not affect the level of Ca2+ pump (SERCA 2b) and calreticulin of intracellular Ca2+ stores. However, IRI resulted in a decrease of IP3 receptor I and altered active Ca2+ accumulation into the ER. A non-specific alteration of physical properties of total membranes such as the oxidative modifications of proteins as well as the content of lipoperoxidation products can also be detected after IRI. ROS can alter physical and functional properties of neuronal membranes. We discuss our results suggesting that ischemia-induced disturbation of ion transport systems may participate in or follow delayed death of neurons after ischemia.

Expression of a P-type Ca(2+)-transport ATPase in Bacillus subtilis during sporulation.

The open reading frame designated yloB in the genomic sequence of Bacillus subtilis encodes a putative protein that is most similar to the typically eukaryotic type IIA family of P-type ion-motive ATPases, including the endo(sarco)plasmic reticulum (SERCA) and PMR1 Ca(2+)-transporters, located respectively in the SERCA and the Golgi apparatus. The overall amino acid sequence is more similar to that of the Pmr1s than to the SERCAs, whereas the inverse is seen for the 10 amino acids that form the two Ca(2+)-binding sites in SERCA. Sporulating but not vegetative B. subtilis cells express the predicted protein, as shown by Western blotting and by the formation of a Ca(2+)-dependent phosphorylated intermediate. Half-maximal activation of phosphointermediate formation occurred at 2.5 microM Ca(2+). Insertion mutation of the yloB gene did not affect the growth of vegetative cells, did not prevent the formation of viable spores, and did not significantly affect 45Ca accumulation during sporulation. However, spores from knockouts were less resistant to heat and showed a slower rate of germination. It is concluded that the P-type Ca(2+)-transport ATPase from B. subtilis is not essential for survival, but assists in the formation of resistant spores. The evolutionary relationship of the transporter to the eukaryotic P-type Ca(2+)-transport ATPases is discussed.

Molecular physiology of the SERCA and SPCA pumps.

Intracellular Ca(2+)-transport ATPases exert a pivotal role in the endoplasmic reticulum and in the compartments of the cellular secretory pathway by maintaining a sufficiently high lumenal Ca(2+) (and Mn(2+)) concentration in these compartments required for an impressive number of vastly different cell functions. At the same time this lumenal Ca(2+) represents a store of releasable activator Ca(2+) controlling an equally impressive number of cytosolic functions. This review mainly focuses on the different Ca(2+)-transport ATPases found in the intracellular compartments of mainly animal non-muscle cells: the sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA) pumps. Although it is not our intention to treat the ATPases of the specialized sarcoplasmic reticulum in depth, we can hardly ignore the SERCA1 pump of fast-twitch skeletal muscle since its structure and function is by far the best understood and it can serve as a guide to understand the other members of the family. In a second part of this review we describe the relatively novel family of secretory pathway Ca(2+)/Mn(2+) ATPases (SPCA), which in eukaryotic cells are primarily found in the Golgi compartment.

The sarco-endoplasmic reticulum Ca2+ ATPase is required for development and muscle function in Caenorhabditis elegans.

The sarco-endoplasmic reticulum Ca(2+)-transport ATPase (SERCA) loads intracellular releasable Ca(2+) stores by transporting cytosolic Ca(2+) into the endoplasmic (ER) or sarcoplasmic reticulum (SR). We characterized the only SERCA homologue of the nematode Caenorhabditis elegans, which is encoded by the sca-1 gene. The sca-1 transcript is alternatively spliced in a similar mode as the vertebrate SERCA2 transcript, giving rise to two protein variants: CeSERCAa and CeSERCAb. These proteins showed structural and functional conservation to the vertebrate SERCA2a/b proteins. The CeSERCAs were primarily expressed in contractile tissues. Loss of CeSERCA through gene ablation or RNA interference resulted in contractile dysfunctioning and in early larval or embryonic lethality, respectively. Similar defects could be induced pharmacologically using the SERCA-specific inhibitor thapsigargin, which bound CeSERCA at a conserved site. The conservation of SERCA2 homologues in C. elegans will allow genetic and chemical suppressor analyses to identify promising drug targets and lead molecules for treatment of SERCA-related diseases such as heart disease.

Baseline cytosolic Ca2+ oscillations derived from a non-endoplasmic reticulum Ca2+ store.

Cytosolic Ca(2+) oscillations can be due to cycles of release and re-uptake of internally stored Ca(2+). To investigate the nature of these Ca(2+) stores, we expressed the Pmr1 Ca(2+) pump of Caenorhabditis elegans in COS-1 cells and pretreated the cells with thapsigargin to prevent Ca(2+) uptake by the sarco(endo)plasmic reticulum Ca(2+)-ATPase. Pmr1 co-localized with the Golgi-specific 58K protein and was targeted to a Ca(2+) store that was less leaky for Ca(2+) than the endoplasmic reticulum and whose inositol trisphosphate receptors were less sensitive to inositol trisphosphate and ATP than those in the endoplasmic reticulum. ATP-stimulated Pmr1-overexpressing cells responded after a latency to extracellular Ca(2+) with a regenerative Ca(2+) signal, which could be prevented by caffeine. They also produced very stable ilimaquinone-sensitive baseline Ca(2+) spikes, even in the presence of thapsigargin. Such responses never occurred in non-transfected cells or in cells that overexpressed the type-1 sarco(endo)plasmic reticulum Ca(2+)-ATPase. Abortive Ca(2+) spikes also occurred in histamine-stimulated untransfected HeLa cells pretreated with thapsigargin, and they too were inhibited by ilimaquinone. We conclude that the Pmr1-induced Ca(2+) store, which probably corresponds to the Golgi compartment, can play a crucial role in setting up baseline Ca(2+) spiking.

The Golgi PMR1 P-type ATPase of Caenorhabditis elegans. Identification of the gene and demonstration of calcium and manganese transport.

In recent years, it has been well established that the Ca(2+) concentration in the lumen of intracellular organelles is a key determinant of cell function. Despite the fact that essential functions of the Golgi apparatus depend on the Ca(2+) and Mn(2+) concentration in its lumen, little is known on the transport system responsible for ion accumulation. The Golgi ion pump PMR1 has been functionally studied only in yeast. In humans, mutations in the orthologous gene ATP2C1 cause Hailey-Hailey disease. We report here the identification of the PMR1 homologue in the model organism Caenorhabditis elegans and after ectopic expression the direct study of its ion transport in permeabilized COS-1 cells. The C. elegans genome is predicted to contain a single PMR1 orthologue on chromosome I. We found evidence for alternative splicing in the 5'-untranslated region, but no indication for the generation of different protein isoforms. C. elegans PMR1 overexpressed in COS-1 cells transports Ca(2+) and Mn(2+) with high affinity into the Golgi apparatus in a thapsigargin-insensitive manner. Part of the accumulated Ca(2+) can be released by inositol 1,4,5-trisphosphate, in agreement with the idea that the Golgi apparatus is an inositol 1,4,5-trisphosphate-sensitive Ca(2+) store.

Abnormal intracellular ca(2+)homeostasis and disease.

A whole range of cell functions are regulated by the free cytosolic Ca(2+)concentration. Activator Ca(2+)from the extracellular space enters the cell through various types of Ca(2+)channels and sometimes the Na(+)/Ca(2+)-exchanger, and is actively extruded from the cell by Ca(2+)pumps and Na(+)/Ca(2+)-exchangers. Activator Ca(2+)can also be released from internal Ca(2+)stores through inositol trisphosphate or ryanodine receptors and is taken up into these organelles by means of Ca(2+)pumps. The resulting Ca(2+)signal is highly organized in space, frequency and amplitude because the localization and the integrated free cytosolic Ca(2+)concentration over time contain specific information. Mutations or functional abnormalities in the various Ca(2+)transporters, which in vitro seem to induce trivial functional alterations, therefore, often lead to a plethora of diseases. Skeletal-muscle pathology can be caused by mutations in ryanodine receptors (malignant hyperthermia, porcine stress syndrome, central-core disease), dihydropyridine receptors (familial hypokalemic periodic paralysis, malignant hyperthermia, muscular dysgenesis) or Ca(2+)pumps (Brody disease). Ca(2+)-pump mutations in cutaneous epidermal keratinocytes and cochlear hair cells lead to, skin diseases (Darier and Hailey-Hailey) and hearing/vestibular problems respectively. Mutated Ca(2+)channels in the photoreceptor plasma membrane cause vision problems. Hemiplegic migraine, spinocerebellar ataxia type-6, one form of episodic ataxia and some forms of epilepsy can be due to mutations in plasma-membrane Ca(2+)channels, while antibodies against these channels play a pathogenic role in all patients with the Lambert-Eaton myasthenic syndrome and may be of significance in sporadic amyotrophic lateral sclerosis. Brain inositol trisphosphate receptors have been hypothesized to contribute to the pathology in opisthotonos mice, manic-depressive illness and perhaps Alzheimer's disease. Various abnormalities in Ca(2+)-handling proteins have been described in heart during aging, hypertrophy, heart failure and during treatment with immunosuppressive drugs and in diabetes mellitus. In some instances, disease-causing mutations or abnormalities provide us with new insights into the cell biology of the various Ca(2+)transporters.

Basic principles of quantitative PCR.

The polymerase chain reaction (PCR) is an extremely sensitive method owing to the repetitive multiplication of template molecules. This property is a drawback for quantitative measurements because small differences in the multiplication factor lead to large differences in the amount of product. Two methods can be used to solve the problem of quantification: kinetic methods based on the determination or comparison of the amplification factor; and coamplification methods, which compare the amount of product to that of a simultaneously amplified standard template. An overview of the theoretical background of both methods is presented. For selection of a suitable method, both theoretical and practical considerations are important. Kinetic methods are the most convenient if PCR can be performed without opening the tubes, as in some apparatus using fluorescence detection. Coamplification methods can be done without expensive equipment but requires the parallel running of several PCR tubes. When the number of initial template molecules is close to one, as in the limiting dilution technique, statistical considerations become important.