Merkmalsanalyse von Uhrzeichnungen als Beitrag zur Diagnostik der Demenz vom Alzheimer Typ

Zusammenfassung: Zur leichteren Anwendbarkeit des in der Demenzforschung mehrfach und in verschiedener Weise benutzten Uhrzeichen-Tests im Rahmen psychodiagnostischer Verfahren sollten Merkmale gefunden werden, die eine diagnostische Differenzierung zwischen «Alzheimer-Patienten», «Depressiven» und «Gesunden» erlauben. Insgesamt 205 Patienten einer «Gedächtnissprechstunde» mit den Diagnosen Demenz vom Alzheimer-Typ (n = 101), Major Depression (n = 58) nach DSM-III-R und «Gesund» (klinisch unauffällig) (n = 46) wurden gebeten, das Zifferblatt einer Uhr mit einer vorgegebenen Zeit zu zeichnen. Anhand von 18 in diesen Zeichnungen empirisch gefundenen Fehlerkategorien wurde nach Unterschieden in den drei Gruppen gesucht. Dabei ergaben sich hochsignifikante Unterschiede in der Häufigkeit der vorkommenden Merkmale sowohl zwischen Gesunden und Depressiven (p = < .0004) als auch zwischen Depressiven und Alzheimer-Patienten (p = < .0001). Eine Diskriminanzanalyse kennzeichnete sechs Fehlerkategorien als signifikante, nicht redundante Prädiktoren für DAT. Drei von ihnen und noch drei weitere, die nur seltener waren, kamen ausschließlich bei DAT vor. Inhaltlich entsprechen diese Fehlerkategorien Verwirrungstendenzen, Unfähigkeit, konzeptgebunden zu denken, und Verlust der Vorstellung des Geforderten, also Störungen der höheren kortikalen Funktionen. Ferner stellte sich heraus, daß sechs der DAT kennzeichnenden Merkmale bei den Depressiven überhaupt nicht vorkamen.

Interaction between the pore and a fast gate of the cardiac sodium channel

Permeant ions affect a fast gating process observed in human cardiac sodium channels (Townsend, C., H.A. Hartmann, and R. Horn. 1997. J. Gen. Physiol. 110:11-21). Removal of extracellular permeant ions causes a reduction of open probability at positive membrane potentials. These results suggest an intimate relationship between the ion-conducting pore and the gates of the channel. We tested this hypothesis by three sets of manipulations designed to affect the binding of cations within the pore: application of intracellular pore blockers, mutagenesis of residues known to contribute to permeation, and chemical modification of a native cysteine residue (C373) near the extracellular mouth of the pore. The coupling between extracellular permeant ions and this fast gating process is abolished both by pore blockers and by a mutation that severely affects selectivity. A more superficial pore mutation or chemical modification of C373 reduces single channel conductance while preserving both selectivity of the pore and the modulatory effects of extracellular cations. Our results demonstrate a modulatory gating role for a region deep within the pore and suggest that the structure of the permeation pathway is largely preserved when a channel is closed.

Free leptin, bound leptin, and soluble leptin receptor in normal and diabetic pregnancies

We measured serum levels of free leptin, bound leptin, and soluble leptin receptor by specific RIA methods in 20 normal and 19 insulin-dependent diabetes mellitus subjects at 20 and 30 weeks gestation and postpartum, and analyzed the data using hierarchical statistical models. Total leptin levels rise from 20-30 weeks gestation (688 +/- 58 to 785 +/- 62 pmol/L, mean +/- SEM; P = 0.009). There is a significant postpartum fall to 445 +/- 47 pmol/L (P < 0.001). This rise is caused by the rise in the bound leptin levels, as there is no significant change in free leptin levels between 20 and 30 weeks (P = 0.17). There is a significant postpartum fall in free leptin levels (P < 0.001). Insulin requirements rise in the third trimester, but despite this there was no significant difference in free or bound leptin levels between the normal and diabetic subjects at any stage [free leptin, 223 +/- 35 and 266 +/- 24, 237 +/- 45 and 223 +/- 27, and 109 +/- 16 and 104 +/- 24 (P = 0.34); bound leptin, 410 +/- 73 and 428 +/- 54, 501 +/- 78 and 562 +/- 71, and 330 +/- 47 and 271 +/- 46 (P = 0.84); for normals and diabetics at 20 and 30 weeks gestation and postpartum, respectively]. Diabetic subjects, however, had significantly higher soluble leptin receptor levels at all stages (P << 0.001), which rose further in the third trimester from 3742 +/- 268 (mean +/- SEM) to 4134 +/- 239 pmol/L, whereas in the normal group there was a fall from 3149 +/- 169 to 2712 +/- 123 (P = 0.05). There is a linear relationship between the soluble leptin receptor levels and the body mass index in the diabetic group only. We conclude that there is no significant difference in free or bound leptin levels between the normal and insulin-dependent diabetic subjects either during pregnancy or postpartum, but female insulin-dependent diabetic subjects have significantly higher soluble leptin receptor levels. We speculate that high soluble leptin receptor levels might be implicated in the development of the leptin resistance in this group.

Elevated nocturnal profiles of serum leptin in patients with depression

Leptin, the protein product of the obese (ob) gene, has been suggested to play a role in the regulation of food intake. As depressive episodes are frequently characterized by loss of appetite, reduced food intake and weight loss, altered leptin secretion might also be expected in patients with depression. Therefore, we examined nocturnal (10.00 p.m. to 7.00 a.m.) secretion of leptin, cortisol, ACTH and growth hormone (GH) in a group of 15 patients with depression and age- and sex-matched controls (age range 23-71 years). In addition, the effects of pulsatile administration of growth hormone-releasing hormone (GHRH), thought to be an endogenous antagonist of corticotropin-releasing hormone (CRH), which in turn is believed to play a critical role for the pathophysiology of depression, on nocturnal hormone secretion were assessed. Patients with depression showed a trend towards elevated nocturnal cortisol secretion (F = 3.8, p < 0.05). Nocturnal serum leptin was significantly higher in patients, despite a reported weight loss (F = 8, p < 0.05), but showed the same sexual dimorphism as in controls (F = 20.9, p < 0.01). No significant differences were seen between patients and controls with regard to plasma GH and ACTH. GHRH treatment increased GH secretion in both patients and controls, while the other hormones were not affected. Furthermore, serum leptin was correlated with body mass index (BMI) in controls, but not in patients with depression, supporting an altered regulation of leptin secretion in depressive illness. Finally, we provide some evidence that in young female patients the normal nocturnal leptin surge is blunted. As glucocorticoids can prevent the fasting-induced decline in serum leptin, we propose that hypercortisolism in depression might counteract the reduction in leptin secretion caused by decreased food intake and weight loss. Elevated serum leptin in depression might in turn further promote CRH release, as shown in animals and, hence, contribute to HPA system hyperactivity seen in depression.

Severe early-onset obesity, adrenal insufficiency and red hair pigmentation caused by POMC mutations in humans

Sequential cleavage of the precursor protein pre-pro-opiomelanocortin (POMC) generates the melanocortin peptides adrenocorticotrophin (ACTH), melanocyte-stimulating hormones (MSH) alpha, beta and gamma as well as the opioid-receptor ligand beta-endorphin. While a few cases of isolated ACTH deficiency have been reported (OMIM 201400), an inherited POMC defect has not been described so far. Recent studies in animal models elucidated a central role of alpha-MSH in the regulation of food intake by activation of the brain melanocortin-4-receptor (MC4-R; refs 3-5) and the linkage of human obesity to chromosome 2 in close proximity to the POMC locus, led to the proposal of an association of POMC with human obesity. The dual role of alpha-MSH in regulating food intake and influencing hair pigmentation predicts that the phenotype associated with a defect in POMC function would include obesity, alteration in pigmentation and ACTH deficiency. The observation of these symptoms in two probands prompted us to search for mutations within their POMC genes. Patient 1 was found to be a compound heterozygote for two mutations in exon 3 (G7013T, C7133delta) which interfere with appropriate synthesis of ACTH and alpha-MSH. Patient 2 was homozygous for a mutation in exon 2 (C3804A) which abolishes POMC translation. These findings represent the first examples of a genetic defect within the POMC gene and define a new monogenic endocrine disorder resulting in early-onset obesity, adrenal insufficiency and red hair pigmentation.

Independent versus coupled inactivation in sodium channels. Role of the domain 2 S4 segment

The voltage sensor of the sodium channel is mainly comprised of four positively charged S4 segments. Depolarization causes an outward movement of S4 segments, and this movement is coupled with opening of the channel. A mutation that substitutes a cysteine for the outermost arginine in the S4 segment of the second domain (D2:R1C) results in a channel with biophysical properties similar to those of wild-type channels. Chemical modification of this cysteine with methanethiosulfonate-ethyltrimethylammonium (MTSET) causes a hyperpolarizing shift of both the peak current-voltage relationship and the kinetics of activation, whereas the time constant of inactivation is not changed substantially. A conventional steady state inactivation protocol surprisingly produces an increase of the peak current at -20 mV when the 300-ms prepulse is depolarized from -190 to -110 mV. Further depolarization reduces the current, as expected for steady state inactivation. Recovery from inactivation in modified channels is also nonmonotonic at voltages more hyperpolarized than -100 mV. At -180 mV, for example, the amplitude of the recovering current is briefly almost twice as large as it was before the channels inactivated. These data can be explained readily if MTSET modification not only shifts the movement of D2/S4 to more hyperpolarized potentials, but also makes the movement sluggish. This behavior allows inactivation to have faster kinetics than activation, as in the HERG potassium channel. Because of the unique properties of the modified mutant, we were able to estimate the voltage dependence and kinetics of the movement of this single S4 segment. The data suggest that movement of modified D2/S4 is a first-order process and that rate constants for outward and inward movement are each exponential functions of membrane potential. Our results show that D2/S4 is intimately involved with activation but plays little role in either inactivation or recovery from inactivation.

rCBF SPECT and the acetazolamide test in the evaluation of dementia

BACKGROUND

The diagnostic potential of 99mTc-HMPAO following systemic administration of the cerebral vasodilator acetazolamide (acetazolamide test) was evaluated using regional-cerebral-blood-flow (rCBF) SPECT in patients with Alzheimer's disease (AD) or with vascular-type of dementia (VD).

METHODS

An initial, high-resolution SPELT study was performed with 99mTc-HMPAO, and after 2 days patients were re-evaluated with 99mTc-HMPAO following systemic administration of acetazolamide. Reconstructed SPELT slices were evaluated visually and semiquantitatively by a semiautomatic rCBF map method.

RESULTS

Using 99mTc-HMPAO alone, a bilateral hypoperfusion was found in the temporal and/or parietal regions in 33% (6/18) of VD patients and in 70% (23/33) of AD patients. The vascular reserve capacity, as determined with the acetazolamide test, was not impaired in 22% of the VD patients but in 76% of the AD patients. The differences in the perfusion patterns between VD and AD patients were statistically different (p < 0.01, Fischer's exact test). Of the 6 VD patients with hypoperfusion (bilateral temporal and/or parietal), 4 had a decreased vascular reserve capacity as determined in the acetazolamide test. Decreased reserve capacity was found in only 4 out of 25 patients with AD.

CONCLUSIONS

The acetazolamide test is helpful in rCBF SPECT to differentiate VD from AD.

[Total illness costs of schizophrenia and monetary evaluation of prevention of recurrence exemplified by a standard depot neuroleptic (flupenthixol decanoate)]

Treatment of patients suffering from schizophrenia is very expensive. However, by consistently and methodically performed medical prophylaxis the disease can be controlled sufficiently well. Regular prophylactic treatment compared to repeated treatment of acute episodes has both medical advantages and reduces cost by reducing the rate of hospitalisation. Prophylactic treatment with Flupentixoldecanoat can save up to 68% of costs.

Rey Auditory-Verbal Learning Test: structure of a modified German version

The Auditory Verbal Learning Test (AVLT) is widely used in scientific research as well as in clinical practice. But there exists little research on the structure of the AVLT. We investigated the structure of a German version of the AVLT and VLMT, in 232 patients of a psychiatric clinic and in 872 patients of an epileptologic clinic. First we stated a theoretical LISREL model relating the observed variables of the VLMT to short-term memory (STM) and long-term memory (LTM) as latent variables. Then we estimated the postulated LISREL model in the two samples. The proposed model showed excellent fit in both samples, and there were no significant deviations between the estimated and the observed covariance matrices. Thus, STM and LTM suffice to explain the structure of the VLMT, and the proposed structural equations model can be used to estimate STM and LTM capacity from VLMT data.

Probing the outer vestibule of a sodium channel voltage sensor

The second and third basic residues of the S4 segment of domain 4 (D4:R2 and D4:R3) of the human skeletal muscle Na+ channel are known to be translocated from a cytoplasmic to an extracellular position during depolarization. Accessibilities of individual S4 residues were assayed by alteration of inactivation kinetics during modification of cysteine mutants by hydrophilic methanethiosulfonate reagents. The voltage dependences of the reaction rates are identical for extracellular application of cationic methanethiosulfonate-ethyltrimethylammonium (MTSET) and anionic methanethiosulfonate-ethylsulfonate (MTSES), suggesting that D4:R3C is situated outside the membrane electric field at depolarized voltages. The absolute rate of R3C modification is 281-fold greater for MTSET than for MTSES, however, suggesting that at depolarized voltages this S4 thiol resides in a negatively charged hydrophilic crevice. The two hydrophobic residues between D4:R2C and D4:R3C in the primary sequence (L1452 and A1453) are not externally exposed at any voltage. An alpha-helical representation of D4/S4 shows that the basic residues D4:R2 and D4:R3 are on the face opposite that of L1452 and A1453. We propose that in the depolarized conformation, the hydrophobic face of this portion of D4/S4 remains in contact with a hydrophobic region of the extracellular vestibule of the S4 channel.

A liquid mixed meal or exogenous glucagon-like peptide 1 (GLP-1) do not alter plasma leptin concentrations in healthy volunteers

Glucagon-like peptide 1 [7-36 amide] (GLP-1) and the obese gene product (leptin) are thought to be involved in the central regulation of feeding. Both may act from the peripheral circulation to influence brain function. To study potential interactions, GLP-1 ([7-36 amide]: 0.4, 0.8 pmol kg-1 min-1 or placebo on separate occasions) was infused intravenously (from -30 to 240 min) into nine healthy volunteers [age 26 +/- 3 years, body mass index: 22.9 +/- 1.6 kg/m2, glycated haemoglobin HbA1c: 5.0% +/- 0.2% (normal: 4.0%-6.2%), creatinine: 1.1 +/- 0.1 mg/dl], and (at 0 min) a liquid test meal (50 g sucrose in 400 ml 8% amino acid, total amino acids 80 g/l) was administered via a nasogastric tube. Plasma leptin (radioimmunoassay, RIA), glucose, insulin (microparticle enzyme immunoassay), C-peptide (enzyme-linked immunosorbent assay) and GLP-1 (RIA) were measured, and statistical analysis was done with repeated-measures ANOVA and Student's t-test. Plasma leptin concentrations were 31 +/- 6 pmol/l in the basal state. They did not change within 240 min after meal ingestion nor in response to the infusion of exogenous GLP-1 [7-36 amide] (P = 0.99 for the interaction of experiment and time) leading to GLP-1 mean plasma levels of 25 +/- 2 and 36 +/- 3 (basal 6 +/- 1) pmol/l. On the other hand, glucose (from basal 4.7 +/- 0.1 to 6.0 +/- 0.2 mmol/l at 15 min, P < 0.05) and insulin (from basal 28 +/- 2 to 325 +/- 78 pmol/l at 45 min, P < 0.05) increased clearly after the meal with placebo. In conclusion, (1) plasma leptin levels in normal human subjects show no short-term changes after feeding a liquid mixed meal and (2) do not appear to be directly influenced by physiological and pharmacological elevations in plasma GLP-1 [7-36 amide] concentrations. This does not exclude interactions at the cerebral (hypothalamic) level or on more long-term temporal scales.

Anomalous effect of permeant ion concentration on peak open probability of cardiac Na+ channels

Human heart Na+ channels were expressed transiently in both mammalian cells and Xenopus oocytes, and Na+ currents measured using 150 mM intracellular Na+. Decreasing extracellular permeant ion concentration decreases outward Na+ current at positive voltages while increasing the driving force for the current. This anomalous effect of permeant ion concentration, especially obvious in a mutant (F1485Q) in which fast inactivation is partially abolished, is due to an alteration of open probability. The effect is only observed when a highly permeant cation (Na+, Li+, or hydrazinium) is substituted for a relatively impermeant cation (K+, Rb+, Cs+, N-methylglucamine, Tris, choline, or tetramethylammonium). With high concentrations of extracellular permeant cations, the peak open probability of Na+ channels increases with depolarization and then saturates at positive voltages. By contrast, with low concentrations of permeant ions, the open probability reaches a maximum at approximately 0 mV and then decreases with further depolarization. There is little effect of permeant ion concentration on activation kinetics at depolarized voltages. Furthermore, the lowered open probability caused by a brief depolarization to +60 mV recovers within 5 ms upon repolarization to -140 mV, indicative of a gating process with rapid kinetics. Tail currents at reduced temperatures reveal the rapid onset of this gating process during a large depolarization. A large depolarization may drive a permeant cation out of a site within the extracellular mouth of the pore, reducing the efficiency with which the channel opens.

Effect of alkali metal cations on slow inactivation of cardiac Na+ channels

Human heart Na+ channels were expressed transiently in both mammalian cells and Xenopus oocytes, and Na+ currents measured using 150 mM intracellular Na+. The kinetics of decaying outward Na+ current in response to 1-s depolarizations in the F1485Q mutant depends on the predominant cation in the extracellular solution, suggesting an effect on slow inactivation. The decay rate is lower for the alkali metal cations Li+, Na+, K+, Rb+, and Cs+ than for the organic cations Tris, tetramethylammonium, N-methylglucamine, and choline. In whole cell recordings, raising [Na+]zero from 10 to 150 mM increases the rate of recovery from slow inactivation at -140 mV, decreases the rate of slow inactivation at relatively depolarized voltages, and shifts steady-state slow inactivation in a depolarized direction. Single channel recordings of F1485Q show a decrease in the number of blank (i.e., null) records when [Na+]0 is increased. Significant clustering of blank records when depolarizing at a frequency of 0.5 Hz suggests that periods of inactivity represent the sojourn of a channel in a slow-inactivated state. Examination of the single channel kinetics at +60 mV during 90-ms depolarizations shows that neither open time, closed time, nor first latency is significantly affected by [Na+]0. However raising [Na+]0 decreases the duration of the last closed interval terminated by the end of the depolarization, leading to an increased number of openings at the depolarized voltage. Analysis of single channel data indicates that at a depolarized voltage a single rate constant for entry into a slow-inactivated state is reduced in high [Na+]0, suggesting that the binding of an alkali metal cation, perhaps in the ion-conducting pore, inhibits the closing of the slow inactivation gate.

UKPDS 20: plasma leptin, obesity, and plasma insulin in type 2 diabetic subjects

We measured plasma leptin and insulin concentrations across a spectrum of obesity in 829 white Caucasian, 154 Afro-Caribbean, and 204 Asian type 2 diabetic subjects. Although the leptin concentrations covered a large range, there were no subgroups of diabetic subjects with very high or low leptin levels that would suggest mutations in the leptin gene or leptin receptor gene comparable to the obese diabetic ob/ob and db/db mice models respectively. In all three ethnic groups, leptin concentrations correlated with body mass index (BMI) in a similar manner to nondiabetic patients and were higher in females than males after adjustment for BMI, with no difference between ethnic groups. In a multivariate regression analysis, plasma leptin was associated with gender and BMI, (both P < 1 x 10(-17)) and with fasting plasma insulin concentrations (P = 5 x 10(-9)). Subjects treated with insulin had both raised insulin and leptin concentrations. When matched for different therapies, gender, and BMI, diabetic subjects with high leptin levels also had high insulin levels (P < 0.0009). High leptin concentrations may in part be influenced by hyperinsulinemia or impaired insulin sensitivity.

Thia fatty acids, metabolism and metabolic effects

(1) The chemical properties of thia fatty acids are similar to normal fatty acids, but their metabolism (see below: points 2-6) and metabolic effects (see below: points 7-15) differ greatly from these and are dependent upon the position of the sulfur atom. (2) Long-chain thia fatty acids and alkylthioacrylic acids are activated to their CoA esters in endoplasmatic reticulum. (3) 3-Thia fatty acids cannot be beta-oxidized. They are metabolized by extramitochondrial omega-oxidation and sulfur oxidation in the endoplasmatic reticulum followed by peroxisomal beta-oxidation to short sulfoxy dicarboxylic acids. (4) 4-Thia fatty acids are beta-oxidized mainly in mitochondria to alkylthioacryloyl-CoA esters which accumulate and are slowly converted to 2-hydroxy-4-thia acyl-CoA which splits spontaneously to an alkylthiol and malonic acid semialdehyde-CoA ester. The latter presumably is hydrolyzed and metabolized to acetyl-CoA and CO2. (5) Both 3- and 4-thiastearic acid are desaturated to the corresponding thia oleic acids. (6) Long-chain 3- and 4-thia fatty acids are incorporated into phospholipids in vivo, particularly in heart, and in hepatocytes and other cells in culture. (7) Long-chain 3-thia fatty acids change the fatty acid composition of the phospholipids: in heart, the content of n-3 fatty acids increases and n-6 fatty acids decreases. (8) 3-Thia fatty acids increase fatty acid oxidation in liver through inhibition of malonyl-CoA synthesis, activation of CPT I, and induction of CPT-II and enzymes of peroxisomal beta-oxidation. Activation of fatty acid oxidation is the key to the hypolipidemic effect of 3-thia fatty acids. Also other lipid metabolizing enzymes are induced. (9) Fatty acid- and cholesterol synthesis is inhibited in hepatocytes. (10) The nuclear receptors PPAR alpha and RXR alpha are induced by 3-thia fatty acids. (11) The induction of enzymes and of PPAR alpha and RXR alpha are increased by dexamethasone and counteracted by insulin. (12) 4-Thia fatty acids inhibit fatty acid oxidation and induce fatty liver in vivo. The inhibition presumably is explained by accumulation of alkylthioacryloyl-CoA in the mitochondria. This metabolite is a strong inhibitor of CPT-II. (13) Alkylthioacrylic acids inhibits both fatty acid oxidation and esterification. Inhibition of esterification presumably follows accumulation of extramitochondrial alkylthioacryloyl-CoA, an inhibitor of microsomal glycerophosphate acyltransferase. (14) 9-Thia stearate is a strong inhibitor of the delta 9-desaturase in liver and 10-thia stearate of dihydrosterculic acid synthesis in trypanosomes. (15) Some attempts to develop thia fatty acids as drugs are also reviewed.

Serum leptin levels following hypothalamic surgery

To study a potential alteration of hypothalamic centers involved in the negative feedback action of leptin on body weight, serum leptin levels were measured in relation to BMI in 18 patients following surgery for a hypothalamic craniopharyngioma (Ctx), and were compared to levels found in 21 patients operated for a pituitary adenoma (Ptx) or in healthy control subjects. All subjects with Ptx received rhGH replacement therapy (0.5 to 2 IU/m2/d), and serum leptin levels were followed in 3 months intervals over 24 months. Serum leptin levels in patients with Ptx were comparable to controls, whereas 7 of the 18 patients with Ctx had higher than expected concentrations for their BMI. GH treatment in Ptx subjects did not alter serum leptin levels. In 5 Ctx patients where preoperative samples were available, weight gain in parallel to an increase in serum leptin levels was observed but only minimal changes in 4 others. Our data support the role of leptin as an important marker of body weight. The rapid increase in serum leptin levels observed in some Ctx subjects suggests that early postoperative measurement of serum leptin levels may help to identify patients at risk of weight gain following hypothalamic destruction.

Serum leptin and weight reduction in female obesity

Leptin, an adipocyte-derived hormone, induces a decrease in food intake and increases energy expenditure via hypothalamic interactions. In animal models obesity can be caused by leptin deficiency or by a dysfunction of the hypothalamic leptin receptor. Using a radioimmunoassay for the determination of leptin in human serum, we measured serum leptin levels in 227 otherwise healthy normal weight (N = 78; body mass index = 16.1-27.7 kg/m2) or obese women (N = 149; body mass index = 27.8-56.7 kg/m2). Fifty-three subjects were followed over a period of 12 weeks under weight reduction (800 kcal/day) and a subgroup of 33 for another 13 weeks after termination of the diet. Body mass index and serum leptin concentrations were measured longitudinally and compared to female controls not under diet. Under baseline conditions, log serum leptin levels were positively related to body mass index with a best fit using a non-linear regression (p < 0.001), indicating an attenuated increase in serum leptin levels with high body mass index. No subgroup with low serum leptin levels could be identified. Weight reduction induced a rapid decrease in serum leptin levels within the first 3 weeks to levels significantly lower than in body mass index-matched controls under normal diet (p < 0.001). This pattern was consistent after 6 and 12 weeks. Serum leptin levels increased again after the end of the diet but remained significantly lower than in the controls despite unrestricted calorie intake over 7 weeks. The rapid and persistent decrease in serum leptin to lower levels than expected from matched controls may explain the pertinent difficulties of obese subjects to cope with weight reduction.

High regeneration rates in anther culture of interspecific sunflower hybrids

Optimization of anther culture with regard to the induction of callus formation and direct embryogenesis was obtained for interspecific hybrids ofH. annuus withH. tuberosus, H. laetiflorus, andH. resinosus by investigating six different induction media and four regeneration media. One media combination (MS-13, MS-R3 and MS-R4) used under different culture conditions (30°C / 35°C and different dark treatments) gave up to 92.7% embryogenic anthers with an average of 8.5 embryos per anther. However, direct embryogenesis as well as callus formation showed a strong genotypec and treatment specific reaction. From 5,600 anthers of the four investigated genotypes more than 2,000 plants could be regenerated. Regenerants were characterized by morphological traits and isozyme analyses to prove their androgenetic origin.

A unique role for the S4 segment of domain 4 in the inactivation of sodium channels

Sodium channels have four homologous domains (D1-D4) each with six putative transmembrane segments (S1-S6). The highly charged S4 segments in each domain are postulated voltage sensors for gating. We made 15 charge-neutralizing or -reversing substitutions in the first or third basic residues (arginine or lysine) by replacement with histidine, glutamine, or glutamate in S4 segments of each domain of the human heart Na+ channel. Nine of the mutations cause shifts in the conductance-voltage (G-V) midpoints, and all but two significantly decrease the voltage dependence of peak Na+ current, consistent with a role of S4 segments in activation. The decreases in voltage dependence of activation were equivalent to a decrease in apparent gating charge of 0.5-2.1 elementary charges (eo) per channel for single charge-neutralizing mutations. Three charge-reversing mutations gave decreases of 1.2-1.9 eo per channel in voltage dependence of activation. The steady-state inactivation (h infinity) curves were fit by single-component Boltzmann functions and show significant decreases in slope for 9 of the 15 mutants and shifts of midpoints in 9 mutants. The voltage dependence of inactivation time constants is markedly decreased by mutations only in S4D4, providing further evidence that this segment plays a unique role in activation-inactivation coupling.

Role of an S4-S5 linker in sodium channel inactivation probed by mutagenesis and a peptide blocker

A pair of conserved methionine residues, located on the cytoplasmic linker between segments S4 and S5 in the fourth domain of human heart Na channels (hH1), plays a role in the kinetics and voltage dependence of inactivation. Substitution of these residues by either glutamine (M1651M1652/QQ) or alanine (MM/AA) increases the inactivation time constant (tau) at depolarized voltages, shifts steady-state inactivation (h infinity) in a depolarized direction, and decreases the time constant for recovery from inactivation. The data indicate that the mutations affect the rate constants for both binding and unbinding of a hypothetical inactivation particle from its binding site. Cytoplasmic application of the pentapeptide KIFMK in Na channels mutated to remove inactivation produces current decays resembling inactivation (Eaholtz, G., T. Scheuer, and W.A. Catterall. 1994. Neuron. 12: 1041-1048.). KIFMK produces a concentration-dependent, voltage-independent increase in the decay rate of MM/QQ and MM/AA currents at positive membrane potentials (Ki approximately 30 microM), while producing only a small increase in the decay rate of wild-type currents at a concentration of 200 microM. Although MM/QQ inactivates approximately 2.5-fold faster than MM/AA in the absence of peptide, the estimated rate constants for peptide block and unblock do not differ in these mutants. External Na+ ions antagonize the block by cytoplasmic KIFMK of MM/AA channels, but not the inactivation kinetics of this mutant in the absence of peptide. The effect of external [Na+] is interpreted as a voltage-dependent knock-off mechanism. The data provide evidence that KIFMK can only block channels when they are open and that peptide block does not mimic the inactivation process.