Presence of two isoforms of Na,K-ATPase with different pharmacological and immunological properties in the rat kidney

Previous studies have demonstrated the presence of two populations of Na,K-ATPase with distinct kinetic, pharmacological and immunological characteristics along the rabbit nephron, indicating that the proximal segments of the nephron express exclusively the ₁ isoform of the catalytic subunit, whereas the collecting duct expresses an ₃-like isoform. Because pharmacological studies have shown the existence of two populations of Na,K-ATPase with different sensitivities to ouabain in the rat cortical collecting duct, which may result from the presence in the same nephron segment of the two isoforms demonstrated in the different segments of the rabbit nephron, the present study was undertaken to characterize the properties of Na,K-ATPase along the rat nephron. Results indicate that each segment of the rat nephron contains two subpopulations of Na,K-ATPase: a component highly sensitive to ouabain (IC₅₀ 5.10^–6 M) which is recognized by an anti- ₃ antibody and another moiety of lower affinity for ouabain (IC₅₀ 5.10^–4 M) which is recognized by an anti- ₁ antibody. Whether these two subpopulations correspond to different isoforms of the subunit of Na,K-ATPase ( ₁ and ₃-like) remains to be determined.     

Ultrasonography gives directly but noninvasively elastic characteristic of human tendon in vivo

To obtain an insight into tendon elasticity during human movement, a real-time ultrasonography was applied to the contracting tibialis anterior muscle. The insertion point of fascicles onto the aponeurosis was clearly visualized, and its position relative to a fixed marker on the skin moved proximally (1) according to the increasing dorsiflexion force (F) with a fixed ankle joint. Notably, the 1 – F relationship in the tendon was found to be quadratic in nature (F = c1²; c=1.48 2.24, r=0.985 0.992, n=9) as has been reported in the isolated tendon, although the F – 1 curves were slightly underestimated in comparison with the stiffness constant estimated from tendon architecture. This underestimation might be caused by changes in the height of the foot arch with the application of force.     

Absence of long-term modulation of ventilation by dead-space loading during moderate exercise in humans

The stability of arterial PCO₂ (P_aCO₂) during moderate exercise in humans suggests a CO₂-linked control that matches ventilation (_E) to pulmonary CO₂ clearance (CO₂). An alternative view is that _E is subject to long-term modulation (LTM) induced by hyperpnoeic history. LTM has been reported with associative conditioning via dead-space (V_D) loading in exercising goats (Martin and Mitchell 1993). Whether this prevails in humans is less clear, which may reflect differences in study design (e.g. subject familiarisation; V_D load; whether or not _E is expressed relative to CO₂; choice of P_aCO₂ estimator). After familiarisation, nine healthy males performed moderate constant-load cycle-ergometry (20 W-80 W-20 W; <lactate threshold, _L): day 1, pre-conditioning, n=3; day 2, conditioning (V_D=1.59 l, doubling _E at 20 W and 80 W), n=8 with 10 min rest between tests; and, after 1 h rest, post-conditioning, n=3. Gas exchange was determined breath-by-breath. Post-conditioning, neither the transient [phase 1, phase 2 (1, 2)] nor steady-state _E exercise responses, nor their proportionality to CO₂, differed from pre-conditioning. For post-conditioning trial 1, steady-state _E was 28.1 (4.7) l min^–1 versus 29.1 (3.8) l min^–1 pre-conditioning, and mean-alveolar PCO₂ (a validated P_aCO₂ estimator) was 5.53 (0.48) kPa [41.5 (3.6) mmHg] versus 5.59 (0.49) kPa [41.9 (3.7) mmHg]; the 1 _E increment was 4.2 (2.9) l min^–1 versus 5.2 (1.9) l min^–1; the 2 _E time-constant () was 64.4 (24.1) s versus 64.1 (25.3) s; _E/CO₂ was 1.12 (0.04) versus 1.10 (0.04); and the _E-CO₂ slope was 21.7 (3.4) versus 21.2 (3.2). In conclusion, we could find no evidence to support ventilatory control during moderate exercise being influenced by hyperpnoeic history associated with dead-space loading in humans.     

Roles of inositol trisphosphate and protein kinase C in the spontaneous outward current modulated by calcium release in rabbit portal vein

We examined the effects of heparin, guanosine nucleotides, protein kinase C (PKC) modulators, such as phorbol 12,13-dibutylate (PDBu) and H-7 on Ca²⁺-dependent K⁺ currents in smooth muscle cells of the rabbit portal vein using the whole-cell patch-clamp technique, to explore the effects of PKC on the oscillatory outward current (I _oo). Neomycin (30 M), an inhibitor of phospholipase C, and intracellular applications of heparin (10 g/ml) and guanosine 5-O-(2-thiodiphosphate) (GDP[S]; 1 mM) partly but consistently inhibited the generation of I _oo, whereas a higher concentration of heparin (100 g/ml) transiently enhanced then suppressed the generation of I _oo. Inhibition of I _oo generation by heparin was more powerful at the holding potential of + 20 mV than at –20 mV. Inositol 1,4,5-trisphosphate (InsP ₃; 30 M) continuously generated I _oo at holding potentials more positive than –60 mV. Noradrenaline (10 M) and caffeine (3–20 mM) transiently augmented, then reduced the generation of I _oo. Heparin (10 g/ml) completely inhibited responses induced by InsP ₃ and noradrenaline, but not those induced by caffeine. Intracellular application of guanosine 5-triphosphate (GTP; 200 M) or low concentrations of guanosine 5-O-(3-thiotriphosphate) (GTP[S]; 3 M) continuously augmented the generation of I _oo. High concentrations of GTP[S] (10 M) transiently augmented, then inhibited I _oo. Neither GTP[S] nor noradrenaline induced the transient augmentation or the subsequent inhibition of I _oo when applied in the presence of GDP[S] (1 mM), neomycin (30 M) or heparin (10 g/ml). PDBu (0.1 M) reduced the generation of I _oo but failed to produce an outward current following application of caffeine (3–5 mM). This action of PDBu was inhibited by pretreatment with H-7 (20 M). In the presence of H-7, GTP[S] continuously enhanced the generation of I _oo. The suppression of the generation of I _oo during application of noradrenaline (10 M) was reduced by pretreatment with H-7. Thus both InsP₃ and protein kinase C contribute to the generation of I _oo in smooth muscle cells of the rabbit portal vein and heparin is not a specific InsP ₃ antagonist on the InsP ₃-induced Ca²⁺-release channel (PIRC). InsP ₃ opens PIRC and protein kinase C may deplete the stored Ca²⁺ by either inhibiting the reuptake of Ca²⁺ or by enhancement of the releasing actions of InsP ₃.     

Phosphorylation-regulated low-conductance Cl− channels in a human pancreatic duct cell line

A low-conductance Cl^– channel has been identified in the apical membrane of the human pancreatic duct cell Capan-1 using patch-clamp techniques. Cell-attached channels were activated by the vasoactive intestinal polypeptide (VIP, 0.1 mol/l), dibutyryl-adenosine 3,5-cyclic monophosphate (db-cAMP, 1 mmol/l), 8-bromo adenosine 3,5-cyclic monophosphate (8-BrcAMP, 1 mmol/l), 3-isobutyl-1-methyl-xanthine (IBMX, 100 mol/l) and forskolin (10 mol/l). No channel activity was observed in non-stimulated control cells. In both cell-attached and excised inside-out patches, the channel had a linear current/voltage relationship and a unitary conductance of 9 pS at 23°C and 12 pS at 37°C. Its opening probability was not voltage dependent although pronounced flickering was induced at negative potentials. Anionic substitution led to the selectivity sequence Cl^–>I^–>HCO₃ ^–>gluconate. In insideout excised patches, the channel activity declined spontaneously within a few minutes. Reactivation of silent excised channels was achieved by adding protein kinase A (PKA, in the presence of ATP, cAMP and Mg²⁺). Conversely, active channels were silenced in the presence of alkaline phosphatase. The PKA-activated Cl^– channel was 4,4-diisothiocyanatostilbene-2,2-disulphonic acid (DIDS, 100 mol/l) and 4-acetamido-4-isothiocyanatostilbene-2, 2-disulphonic acid (SITS, 100 mol/l) insensitive, but was blocked by diphenylamine-2-carboxylic acid (DPC, 100 mol/l). These results demonstrate that the apical low-conductance Cl^– channel in Capan-1 is regulated on-cell by VIP receptors via cAMP and off-cell by PKA and phosphatases. They provide evidence that this channel is closely related to the cystic fibrosis transmembrane conductance regulator (CFTR) Cl^– channel.     

Helothermine,a lizard venom toxin,inhibits calcium current in cerebellar granules

Helothermine (HLTx), a 25.5-kDa peptide toxin isolated from the venom of the Mexican beaded lizard (Heloderma horridum horridum), was found to be an inhibitor of Ca²⁺ channels in cerebellar granule cells of newborn rats. Macroscopic currents, carried by 10 mM Ba²⁺, were measured in whole-cell configuration. The toxin at the saturating dose of 2.5 M reversibly produced an 67% block of the voltage-dependent Ca²⁺ current by a fast mechanism of action. The current inhibition and recovery were reached in less than 1 min. Inhibition was concentration-dependent, with a half-effective dose of 0.25 M. The current block was practically voltage-independent, whereas the steady-state inactivation h was significantly affected by HLTx (10 mV). The toxin did not affect the activation and inactivation kinetics of the Ca²⁺ current. Experiments with other Ca²⁺ channel blockers showed that HLTx abolished -conotoxin GVIA-sensitive Ca²⁺ currents, as well as -AgaIVA- and dihydropyridine-sensitive Ca²⁺ currents. These drugs had virtually no effect when HLTx was applied first. The present results indicate that HLTx produce a high-potency blockage of the three pharmacologically distinct Ca²⁺ current components.     

Neuronal nicotinic acetylcholine receptors expressed in Xenopus oocytes: role of the α subunit in agonist sensitivity and desensitization

Neuronal nicotinic acetylcholine receptors (nAChRs) were expressed in Xenopus laevis oocytes after nuclear injection of complementary deoxyribonucleic acid (cDNA) expression vectors. The two receptor subtypes 4/n1 and 3/n1 were readily distinguishable from one another by ACh sensitivity and desensitization. 3/n1 receptors showed lower ACh sensitivity and stronger desensitization than 4/n1 receptors. Furthermore, although the current/voltage relationship was very similar in both receptor subtypes, the voltage dependence of desensitization was found to be strikingly different. As the n1 subunit was unchanged, the subunits must be responsible for these functional differences. Symmetric hybrid cDNAs, 43 and 34, were constructed and functional receptors were obtained by co-injection with n1. These hybrid receptors displayed an ACh sensitivity that was mainly defined by the extracellular sequence of the subunit. In contrast, no part of the subunit was found fully to determine desensitization.     

Die Nebennierenrindenfunktion unter Applikation von 9α-Fluorcortisol

Zusammenfassung Untersuchungen über den Einfluß von 9-Fluorcortisol auf die Nebennierenrindenfunktion ergaben — in Verbindung mit in der Literatur mitgeteilten Werten — eine dosisabhängige Einschränkung der Ausscheidung von Nebennierenrindenhormonen. Die Ansprechbarkeit der Nebennierenrinde auf exogenes ACTH bleibt erhalten. Es ist daher eine Hemmung der hypophysären ACTH-Sekretion anzunehmen, die durch die Struktur des synthetischen Steroids erklärbar ist. — In geringer Dosierung, wie sie als Erhaltungsdosis bei Langzeittherapie verabfolgt wird, verursacht 9-Fluorcortisol keine wesentliche Einschränkung der Hormonausscheidung.

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Effect of 9-fluorocortisol on adrenocortical function

Summary Investigation of adrenal cortical function during administration of 9-fluorcortisol revealed—in connection with results obtained from the literature—a dose-related inhibition of the secretion of adrenocortical hormones. Adrenal cortical response to exogenous ACTH remains unaffected. An inhibition of hypophyseal ACTH-secretion is therefore assumed, caused by the structure of the synthetic steroid. At low dosage, as applied in long-term treatment, no significant alteration of steroid excretion patterns was observed.

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Astonin-H, Hersteller: Fa. E. Merck A.G., Darmstadt.

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In der Arbeit werden folgende Abkürzungen verwendet: 17-KS=17-Ketosteroide; 17-OH-CS=17-Hydroxycorticosteroide; F=Cortisol=Pregn-4-en-11,17,21-triol-3,20-dion; E=Cortison=Pregn-4-en-17,21-diol-3,11,20-trion; THF=Tetrahydrocortisol=5-Pregnan-3,11,17,21-tetrol-20-on; allo-THF=allo-Tetrahydrocortisol=5-Pregnan-3,11,17,21-tetrol-20-on; THE=Tetrahydrocortison=5-Pregnan-3,17,21-triol-11,20-dion; Andro=Androsteron=5-Androstan-3-ol-17-on; Ätio=Ätiocholanolon=5-Androstan-3-ol-17-on; DHA=Dehydroepiandrosteron=Androst-5-en-3-ol-17-on.

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Herrn Prof. Dr. med. H. Franke zum 60. Geburtstag gewidmet.     

Cationic proteins of human granulocytes Effects on human platelet aggregation and serotonin release

Immune-aggregate and thrombin-mediated [³H]serotonin release from human platelets are shown to be enhanced when platelets are preincubated with the antibacterial chymotrypsin-like cationic protein isolated from human granulocytes. The enhancement is dose dependent and inhibited by heating of the cationic protein. Release with chymotrypsin-like cationic protein alone was not observed, although the protein was shown to micro-aggregate platelets irreversibly by an ADP-dependent reaction. Platelet macro-aggregation induced by immune-aggregate was also enhanced by chymotrypsin-like cationic protein whereas platelet macro-aggregation induced by thrombin was inhibited competitively. Platelet micro-aggregation induced by chymotrypsin-like cationic protein was inhibited when preincubated for more than 5 min with a 2-fold molar excess of-1-antitrypsin. Chymotrypsin-like cationic protein interaction with several platelet reactions suggests a close relationship between neutrophils and platelets in the inflammatory process.     

On the regulation of the expressed L-type calcium channel by cAMP-dependent phosphorylation

The Ca²⁺ channel subunits _1C-a and _1C-b were stably expressed in Chinese hamster ovary (CHO) and human embryonic kidney (HEK) 293 cells. The peak Ba²⁺ current (I _Ba) of these cells was not affected significantly by internal dialysis with 0.1 mM cAMP-dependent protein kinase inhibitor peptide (mPKI), 25 M cAMP-dependent protein kinase catalytic subunit (PKA), or a combination of 25 M PKA and 1 M okadaic acid. The activity of the _1C-b channel subunit expressed stably in HEK 293 cells was depressed by 1 M H 89 and was not increased by superfusion with 5 M forskolin plus 20 M isobutylmethylxanthine (IBMX). The _1C-a·₂·₂/ complex was transiently expressed in HEK 293 cells; it was inhibited by internal dialysis of the cells with 1 M H 89, but was not affected by internal dialysis with mPKI, PKA or microcystin. Internal dialysis of cells expressing the _1C-a·₂·₂/ channel with 10 M PKA did not induce facilitation after a 150-ms prepulse to +50 mV. The Ca²⁺ current (I _Ca) of cardiac myocytes increased threefold during internal dialysis with 5 M PKA or 25 M microcystin and during external superfusion with 0.1 M isoproterenol or 5 M forskolin plus 50 M IBMX. These results indicate that the L-type Ca²⁺ channel expressed is not modulated by cAMP-dependent phosphorylation to the same extent as in native cardiac myocytes.     

Effects of inhibitors and ion substitutions on oscillations of cell membrane potential in cells expressing the RAS oncogene

Previous studies revealed that in NIH fibroblasts expressing the ras oncogene but not in other NIH fibroblasts, bradykinin leads to sustained, calcium dependent oscillations of cell membrane potential by repetitive activation of calcium-sensitive K⁺ channels. The present study has been performed to test for ion and inhibitor sensitivity of these oscillations. Both, Lys-bradykinin (kallidin) and bradykinin, but not any shorter peptide tested, maintained the oscillations. The oscillations are abolished in the presence of the K⁺ channel blocker barium (10 nmol/l). The amplitude but not the frequency of the oscillations is dependent on the extracellular potassium concentration. The oscillations are not dependent on the presence of extracellular sodium, bicarbonate or chloride. The oscillations are abolished in the absence of extracellular calcium and their frequency is significantly decreased at reduced extracellular calcium (to 0.2 mmol/l). The oscillations are not inhibited by acute administration of ouabain (0.1 mmol/l), by dimethylamiloride (100 mol/l), furosemide (1 mmol/l) and hydrochlorothiazide (100 mol/l), by cobalt (100 mol/l), zinc (100 mol/l), gadolinium (100 mol/l), verapamil (10 mol/l) and diltiazem (10 mol/l), but are abolished in the presence of 100 mol/l lanthanum, 1 mmol/l cadmium, 10 mol/l nifedipine, 25 mol/l SK & F 96365 and 200 mol/l TMB-8. Stimulation of calcium entry by 10 mol/l ionomycin is frequently followed by oscillations of cell membrane potential even in the absence of bradykinin. In conclusion, in cells expressing the ras oncogene bradykinin leads to sustained activation of calcium channels at the cell membrane, which cause oscillations of the cell membrane potential by triggering intracellular calcium release.     

Harnsteroidprofile bei Cushing Syndrom und Tumoren der Nebennierenrinde

Summary The analysis of 24-h excretion profiles of urinary steroids in 18 patients suffering from Cushing's syndrome or adrenocortical tumors revealed typical patterns when compared to 37 healthy control persons, 24 patients with obesity, and 6 patients with hirsutism. The validation of eight criteria — increased excretion of free cortisol, 6-hydroxycortisol, 20-dihydrocortisol, 11-hydroxyandrosterone, and 3-hydroxy-5-en steroids, decreased ratio of tetrahydrocortisone (THE) to tetrahydrocortisol (THF), and increased ratios of THF to allotetrahydrocortisol (a-THF) and metabolites of androgens (AM) to metabolites of cortisol (CM) — afforded reliable detection of disorders in steroid biosynthesis. The analysis of urinary steroid profiles can therefore be recommended as a screening procedure in patients with clinical symptoms of disorders in steroid production and/or metabolism.

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Abkürzungen An Androsteron - Aet Aetiocholanolon - AM Androgenmetaboliten: An plus Aet - 11-O-An 11-Ketoandrosteron - 11-OH-An 11-Hydroxyandrosteron - 11-OH-Aet 11-Hydroxyaetiocholanolon - DHEA Dehydroepiandrosteron - 16-OH-DHEA 16-Hydroxydehydroepiandrosteron - 16-OH-DHEA 16-Hydroxydehydroepiandrosteron - A⁵T-16 Androsten-3,16,17-triol - P⁵T Pregnentriol-3-hydroxy-5-en Steroide: DHEA plus Androstendiole plus 16-OH-DHEA plus 16-OH-DHEA plus - P⁵D Pregnendiol plus A⁵T-16 plus 16-Hydroxypregnenolon plus P⁵T - THE Tetrahydrocortison - THF Tetrahydrocortisol - a-THF Allotetrahydrocortisol - CM Cortisolmetaboliten: THE plus THF plus a-THF. - -C,-C Cortole - -CL,-CL Cortolone - 6-OH-F 6-Hydroxycortisol - 20-OH-F 20-Dihydrocortisol - NNR Nebennierenrinde - CRF Corticotropin Releasing Hormon - ACTH Adrenocorticotropes Hormon - CPB Competitive Protein Binding - RIA Radioimmunoassay - HPLC High Pressure Liquid Chromatography - DHEAS Dehydroepiandrosteron-Sulfat. Mit Unterstützung der Deutschen Forschungsgemeinschaft, Ho-471/5-1     

ω-Grammotoxin blocks action-potential-induced Ca2+ influx and whole-cell Ca2+ current in rat dorsal-root ganglion neurons

Field-potential stimulation of rat dorsal-root ganglion (DRG) neurons evoked action-potential-mediated transient increases in intracellular free calcium concentration ([Ca²⁺]_i) as measured by indo-1-based microfluorimetry. Field-potential-evoked [Ca²⁺]_i transients were abolished by tetrodotoxin, and their dependence on stimulus intensity exhibited an abrupt threshold. -Conotoxin GVIA (-CgTx, 100 nM) inhibited action-potential-mediated Ca²⁺ influx by 79%, while nitrendipine (1 M) had little effect. -Grammotoxin SIA (-GsTx, 267 nM), a peptide toxin purified from the venom of the tarantula spider, Grammostola spatulata, blocked action-potential-mediated Ca²⁺ influx as effectively as did -CgTx, suggesting that -GsTx blocks N-type Ca²⁺ channels. In contrast to block by -CgTx, the block produced by -GsTx reversed upon washout of the peptide. -GsTx (270 nM) blocked 80%, and -CgTx (1 M) blocked 64%, of whole-cell Ca²⁺ current (I _Ca) elicited by step depolarization to 0 mV from a holding potential of –80 mV. -GsTx completely occluded inhibition of I _Ca by -CgTx. However, when applied after -CgTx, -GsTx produced an additional inhibition of 27%, indicating that -GsTx also blocked a non-N-type Ca²⁺ channel. BayK8644 (1 M) elicited an increase in I _Ca in the presence of maximally effective concentrations of -GsTx, suggesting that -GsTx does not block L-type channels. Thus, -GsTx displays a selectivity for Ca²⁺ channel subtypes which should prove useful for studying Ca²⁺ channels and Ca²⁺-channel-mediated processes.     

Characterization and localization of α-connectin (titin 1): An elastic protein isolated from rabbit skeletal muscle

Summary A simplified procedure to isolate-connectin (titin 1, TI), a gigantic elastic protein, from rabbit skeletal muscle is described. A rapid column chromatography step to concentrate-connectin is introduced. Separation of-connectin from-connectin is introduced. Separation of-connectin from-connectin (titin 2, TII) in the presence of 4 M urea at pH 7.0 did not cause any change in the secondary structure of-connectin as judged by circular dichroic spectra. Ultraviolet absorption spectra and the amino acid composition of-connectin (MW, approximately 3×10⁶) were similar to those of its proteolytic product,-connectin (MW, approximately 2×10⁶). Circular dichroic spectra suggested that both- and-connectin consist of 60%-sheet and 30%-turn. It thus appears that the whole elastic filament of connectin has a folded-strand structure. Proteolysis of-connectin by calpain resulted in formation of-connectin and smaller peptides. The-connectin interacted with both myosin and actin filaments similarly to-connectin. Polyclonal antibodies raised against 1200 kDa peptides obtained from aged rabbit skeletal myofibrils reacted with-connectin (titin 1, TI) but only weakly with-connectin (titin 2, TII) in rabbit skeletal muscle. Immunoelectron microscopy and indirect immunofluorescence microscopy revealed that the antibodies bound at the Z-line and at the epitope regions in the I-band near the binding site of a monoclonal antibody SMI whose position depends on sarcomere length. It thus appears that-connectin extends from the edge of M-line to the above epitope region in the I-band.     

Expression and ligand-binding function of the integrin α4β1 (VLA-4) on neural-crest-derived tumor cell lines

Human neural-crest-derived tumor cell lines, including three neuroblastomas, an astrocytoma, a glioblastoma, a rhabdomyosarcoma and a melanoma were screened for the expression of the integrin ₄₁ (VLA-4). The neuroblastomas IMR-32 and SK-N-SH, the astrocytoma 131-INI, the glioblastoma Fogerty and the rhabdomyosarcoma TE-671 expressed ₄₁ as determined by cytofluorometry and immunoprecipitation. Another neuroblastoma line, LA-N-1, did not express ₄₁. Analysis of immunoprecipitated ₄₁ showed that the ₄ subunit from the various cell types differed in relative molecular weight (M _r ). The variability in the observed M _r could be accounted for by differences in the levels of N-linked glycosylation. The observed variability in M _r did not appear to affect function since intact cells and solubilized ₄₁ bound to a synthetic peptide identical in sequence to the CS-1 region of the alternatively spliced IIICS domain of fibronectin, a known ₄₁, ligand.     

Prediction of peak torque and contraction work at different isokinetic angular velocities of plantarflexion

Summary Contraction work (CW) and peak torque (PT) of maximum isokinetic plantar flexions were measured in clinically healthy subjects randomly chosen from the official census list of Umeå, Sweden, in three groups: 40–44, 50–54 and 60–64 years of age, with similar proportions of men and women. Maximum isokinetic plantarflexions were performed at angular velocities of 30, 60, 120 and 180 · s^–1. Body-weight, height and crural circumference were measured. Subjects rated their levels of leisure and occupational activities.To establish formulae to predict CW and PT, stepwise regression procedures were applied. The predictive powers (r ²) of the formulae which incorporated age, sex and crural circumference, were higher for PT (30 · s^–1: 0.82, 60 · s^–1: 0.79, 120 · s^–1: 0.75, 180 · s^–1: 0.56) than for CW (30 s^–1: 0.63, 60 s^–1: 0.63, 120 s^–1: 0.60, 180 s^–1: 0.52). Thus the part of the variance explained decreased with increasing angular velocity, but more than 50% was still explained at 180 s^–1.The results indicate that the mechanical output of the plantar flexors is predictable.     

Genetic characterization of an α-specific gene responsible for sexual agglutinability in Saccharomyces cerevisiae: mapping and gene dose effect

Summary A recessive ag1 mutation leads to specific defect in sexual agglutinability specifically in cells of the yeast Saccharomyces cerevisiae. The cryptopleurine resistance gene cry^R 1, closely linked to the mating type locus, was used to select / strains which emerged from / strains by mitotic nonreciprocal recombination, to genetically analyse ag1, since ag1 is expressed only in mating type. The ag1 gene was found to be linked to the centromere tightly, to met3 at 4.4 cM, and to ilv3 at 12 cM on chromosome X. Sexual agglutinability of cells was shown to be dependent on the dose of the AG1 gene, using / isogenic strains carrying AG1/AG1, AG1/ag1 or ag1/ag1. The sst2-1 mutation did not suppress the ag1 mutation. Based on these results, function of the AG1 gene is discussed.Abbreviations cM centimorgan - FDS first division segregation - NPD nonparental ditype - PD parental ditype - SDS second division segregation - TT tetratype     

Modulation of calcium current by ATP in guinea-pig adrenal chromaffin cells

The effects of extracellular adenosine 5-triphosphate (ATP) on voltage-dependent Ca²⁺ currents were examined using the whole-cell voltage-clamp technique in guinea-pig isolated adrenal chromaffin cells. ATP (500 M) reversibly suppressed Ca²⁺ currents in the presence of 5 mM Ca²⁺ in the extracellular solution. The inhibitory effect of ATP on Ca²⁺ currents tended to increase with increases in the peak amplitude of ATP-evoked current when the intracellular solution contained 0.1 or 1 mM ethylenebis(oxonitrilo)tetraacetate(EGTA). Using the intracellular solution containing 10 mM EGTA, on the other hand, the inhibitory efftect did not change regardless of the amplitude of current responses to ATP In the presence of 10 mM Ba²⁺, ATP (100 mol/l). reduced Ba²⁺ currents in a manner similar to Ca²⁺ currents. This reduction was decreased by dialysis of cells with the internal solution containing guanosine 5-O-(2-thiodiphosphate) (GDP [-S]; 1 mM) or guanosine 5-O-(3-thiotriphos-phate) (GTP [-S]; 100 mol/l). A depolarizing prepulse channels. In addition, ATP seems to modulate Ca²⁺ channels via the pathway related to G-protein. Adenine nucleotides and adenosine may play a role in controlling secretory activity in guinea-pig adrenal chromaffin cells.     

The role ofγδ T cells in the normal and disordered immune system

Summary A small population of T cells does not express the conventional T cell receptor characterized by the and polypeptide chains (TCR) but instead, two polypeptides termed and (TCR). This alternative receptor is able to recognize antigen. It appears early in T cell ontogeny, but its role in the thymus prior to the availability of TCR remains unclear. In selected sites such as skin or gut TCR predominates in mice which might suggest a role of T cells in the first line of defense against infection, T cells secrete lymphokines and display cytotoxic activity. However, their activation requirements may differ from what is known for T cells since MHC-nonrestricted and also CD4 and CD8 negative T cells have been described. Preferential activation by mycobacterial antigens possibly indicates a special repertoire of the T cells. In various diseases slightly increased numbers of T cells were found, but these preliminary studies have not yet provided evidence for a major pathogenetic role of T cells.List of abbreviations C constant region (immunoglobulin or TCR gene segment) - CD4 cluster of differentiation 4 (mainly on helper cells) - CD8 cluster of differentiation 8 (mainly on cytotoxic cells) - D diversity region (immunoglobulin or TCR gene segment) - DNA desoxyribonucleic acid - IL2 interleukin 2 - J joining region (immunoglobulin or TCR gene segment) - kD kiloDalton - MHC major histocompatibility complex - NK natural killer (cells) - RA rheumatoid arthritis - TCR T cell receptor - V variable region (immunoglobulin or TCR gene segment)     

Binding of human fibrinogen and its polypeptide chains to group B streptococci

Of 51 group-B streptococcal cultures, 20 bound¹²⁵I-labelled human fibrinogen. In contrast to the streptococci of groups A, C and G, the group-B streptococci interacted more with the, -chain of fibrinogen than with whole fibrinogen. None of the streptococcal cultures reacted with-chain. The fibrinogen-negative group-B streptococci still bound the, -chain. The binding of¹²⁵I-labelled,, -chain could be inhibited by unlabelled fibrinogen with fibrinogen-positive, but not with fibrinogen-negative streptococci of group B.