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Biomedical subjects

H Schindler

Publications and source records attributed to H Schindler.

At least 73 records · Page 4Linked to original sources
PubMed1992

The dihydropyridine niguldipine inhibits T-type Ca2+ currents in atrial myocytes.

The whole-cell tight seal recording technique was used to investigate the effects of niguldipine, a novel dihydropyridine, on Ca2+ currents in guinea pig atrial cells. Ca2+ currents were separated into T-type and L-type components by an appropriate voltage protocol. Extracellular application of 1 microM (+/-)-niguldipine (NIG) resulted in a pronounced blockade of both T-type (to 20 +/- 10% of control, n = 5) and L-type Ca2+ currents (to 28 +/- 12% of control, n = 5). Current to voltage relationships clearly showed that both Ca2+ currents were blocked over the whole voltage range examined (-60 to +40 mV). The inhibitory effect of niguldipine on T-type Ca2+ currents was found to be voltage-dependent, i.e. prolonged hyperpolarization to -90 mV led to a partial and transient removal of NIG block. The IC50 for T-type Ca2+ current inhibition by (+/-)-NIG was determined as 0.18 microM. NIG action is stereospecific. (+)-niguldipine was found to be more potent than (-)-niguldipine in blocking both Ca2+ currents. This study demonstrates the Ca2+ antagonistic action of the dihydropyridine NIG, which may not discriminate between T- and L-type Ca2+ channels.

Animals↗
PubMed1992

Scanning force microscopy studies of the S-layers from Bacillus coagulans E38-66, Bacillus sphaericus CCM2177 and of an antibody binding process.

In many prokaryotic cells (eubacteria and archaebacteria) the outermost cell envelope component is composed of a regularly structured protein surface layer (S-layer). The two-dimensional S-layer from Bacillus coagulans E38-66 and Bacillus sphaericus CCM2177 has been investigated by SFM at molecular resolution under physiological conditions (i.e., in buffer solution). We find the E38-66 S-layer lattice to be oblique with lattice parameters of a = 9-10 nm, b = 7-8 nm and gamma = 80 degrees -90 degrees (E38-66). The CCM2177 lattice is square with a = 12-14 nm, in good agreement with TEM data. We have used the unique possibility of the SFM to study the kinematics of biological processes and have performed experiments on the adhesion of polyclonal antibodies to the recrystallized E38-66 protein layer on a time scale of about two to ten seconds per image frame. This represents a first step in directly visualizing molecular recognition reactions.

Antibodies, Bacterial↗
PubMed1991

Immunologically activated chloride channels involved in degranulation of rat mucosal mast cells.

Crosslinking of type I Fc epsilon receptors (Fc epsilon RI) on the surface of basophils or mast cells initiates a cascade of processes leading to the secretion of inflammatory mediators. We report here a correlation between mediator secretion and the activation of Cl- channels in rat mucosal-type mast cells (line RBL-2H3). Stimulation of RBL cells by either IgE and antigen or by a monoclonal antibody specific for the Fc epsilon RI, resulted in the activation of Cl- ion channels as detected by the patch-clamp technique. Channel activation occurred slowly, within minutes after stimulation. The channel has a slope conductance of 32 pS at potentials between 0 and -100 mV, and an increasing open-state probability with increasing depolarization. Activation of apparently the same Cl- channels could be mimicked without stimulation by isolating inside-out membrane patches in tyrode solution. Parallel inhibition of both Cl- channel activity and mediator secretion, as monitored by serotonin release, was observed by two compounds, the Cl- channel blocker 5-nitro-2-(3-phenylpropylamino) benzoic acid (NPPB) and the anti-allergic drug cromolyn. NPPB inhibited both the antigen-induced Cl- current and the serotonin release, where half-maximal inhibition occurred at similar doses, at 52 microM and 77 microM, respectively. The drug cromolyn, recently found to inhibit immunologically induced mediator secretion from RBL cells upon intracellular application, also blocks Cl- channels (IC50 = 15 microM) when applied to the cytoplasmic side of an inside-out membrane patch. The observed Cl- channel activation upon immunological stimulation and the parallel inhibition of channel current and of serotonin release suggests a functional role for this Cl- channel in mediator secretion from the mast cells studied.

Animals↗
PubMed1991

Lipid-protein surface films generated from membrane vesicles: selfassembly, composition, and film structure.

Lipid-protein films at the air-water interface were generated from a variety of native vesicles and from vesicles derived from lipid extracts. A technique is described which is particularly suitable for the generation of films from small amounts of material at high yield and velocity. In all instances, 10 microliters vesicle suspensions containing 25 micrograms protein yield at least 50 cm2 film area at a constant surface pressure of 12 mN/m within minutes. Upon formation, surface films are separated from vesicles by use of shear forces. Complete separation is demonstrated by electron microscopy and surface pressure-area diagrams. The latter confirms previous conclusions that surface films generated from lipid vesicles are organized as a monolayer. Analysis of lipid-protein surface layers reveals that their lipid to protein ratios match those of the vesicles used, within a factor of two, irrespective of whether films are generated at high or low surface pressure. Surface denaturation of membrane proteins is shown to be effectively prevented when the film is generated and held at high surface pressure (greater than or equal to 15 mN/m). Upon surface pressure jumps from high to low values, denaturation kinetics revealed activation areas of 1.5 (+/- 0.2) nm2.

Animals↗
PubMed1991

Calpastatin and nucleotides stabilize cardiac calcium channel activity in excised patches.

The activity of single L-type Ca2+ channels is rapidly lost (run-down) when contact between the membrane and cytosol is interrupted. We have now achieved the stabilization of cardiac Ca2+ channel activity of guinea-pig ventricular myocytes by using either cytosol or defined components added to excised patches. The endogenous protease inhibitor, calpastatin, together with nucleotides, ATP + GTP, was found to prevent run-down as effectively as cardiac cytosolic solution. These results suggest the involvement of proteolysis by calpain in run-down of channel activity and enable the study of cardiac Ca2+ channel regulation with free access to both sides of the membrane.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1991

Factors affecting response of groups of dairy cows managed for different calving-conception intervals.

Factors which positively or adversely affect the response of cow groups to different planned conception periods were analyzed and quantified. Cows were randomly assigned to groups for breeding at postpartum intervals of 35 to 59, 60 to 90 and 120 to 150 days in a research herd, or 60 to 90 and 120 to 150 days in a cooperating commercial herd, with a planned preceding dry period of 60 days in both herds. Breeding at 35 to 59 and 60 to 90 days post partum resulted in a lower conception rate among multiparous cows but had no effect on primiparous cows. Genital disorders such as metritis, retained placenta, vulva inflammation and vaginitis, did not affect the start of luteal activity or length of the subsequent cycles, but caused a significant delay of the first behavioral estrus and, consequently, a delay of the first insemination in the earlier breeding groups. About 30% of the cows in the different categories were inseminated three or more times and were considered to be repeat breeders. Response rates (number of cows conceiving on time/number assigned) in the later breeding group improved due to higher submission rates (number of cows submitted on time/number assigned), and the conception rates were higher (number of cows conceiving on time/number submitted). The rates in all groups were adversely affected by repeat breeding and genital disorders. The latter delayed the first insemination and the conception rate.

Journal Article↗
PubMed1991

Purified IP3 receptor from smooth muscle forms an IP3 gated and heparin sensitive Ca2+ channel in planar bilayers.

The IP3 receptor of aortic smooth muscle, purified to near homogeneity, was incorporated into vesicle derived planar bilayers. The receptor forms channels which are gated by Ins(1,4,5)P3 (0.5 microM) and are permeable to Ca2+ (Ca2+ greater than K+ much greater than Cl-). Channel activation is specific for Ins(1,4,5)P3. Essentially no activation of channel currents was found for Ins(1,3,4)P3 or Ins(1,3,4,5)P4 at 10 microM. Heparin (25 micrograms/ml) blocked induced currents completely at all levels of activity while ATP (50 microM) increased mean current levels 2 to 4 fold. Ins(1,4,5)P3 activated mean currents increased non-linearly with voltage above about -40 mV applied voltage. Mean current levels could be reversibly adjusted by voltage to the single channel level (0 to -50 mV) or to macroscopic levels (-50 to -100 mV) over periods exceeding 1 h. Single channel events are characterized by fast transitions between predominantly non-resolved sublevels. Estimates of maximal single event currents yield a slope conductance of 32 +/- 4 pS (0 to -60 mV, 50 mM CaCl2). Thus, the purified IP3 receptor forms a channel with functional properties characteristic of IP3 triggered Ca2+ release.

Animals↗
PubMed1989

The cardiac sodium channel shows a regular substate pattern indicating synchronized activity of several ion pathways instead of one.

Cardiac sodium channel substates were induced by using different gating modifiers, namely S-DPI 201-106 (s), toxin II from Anemonia sulcata (a), veratridine (v) and mixtures of these agents (s + v, a + v). Current ratios (normalized substate currents), slope conductances, reversal potentials and saturation characteristics were evaluated for the individual channel substates. The results can be summarized as follows: (i) Current ratios fell into a pattern of six equidistant values (I to VI) irrespective of the modification applied (0.20, 0.34, 0.51, 0.69, 0.85, 1.00). Slope conductances, determinable for substates II, V and VI (4.8, 11.7 and 14.0, respectively), are also consistent with six conductance substates which are integer multiples of a smallest conductance (state I). (ii) The permeability ratio PNa+/PK+ (i.e., reversal potential of substate currents) of the sodium channel was conserved both for different modifications, i.e., by s, a, s + v and a + v, and for the different substates (at least for II, IV and VI) observed for each modification. (iii) Sodium binding to the channel is substate independent. Analysis of slope conductances of states II and VI for three sodium chloride concentrations (71.5, 140 and 303 mM) revealed different maximal conductances (geVImax = 2.9.geIImax) but similar apparent affinities for sodium (KNa + VI = 286 mM; KNa + II = 303 mM). These findings are shown to seriously challenge the commonly unquestioned conception that 'single-current events' reflect ion passage through only one single pathway. The alternative view, that not one pore, but either six or three pores with synchronized gating ('oligochannel') underlie 'single-channel events', is shown to readily account for the observed substate properties and appears not to contradict known properties of 'the sodium channel'. This fundamentally new view of the sodium channel aims to invoke further efforts to distinguish between conceptually distinct models of structure-function relationships for a variety of channels which show multiple substates and conserved ion selectivity.

Animals↗
PubMed1989

[The current risk of gallbladder and bile duct surgery].

The lethal operative risk in gallbladder and bile duct operations decreased from 2.16% in the period 1964-1976 to 1.32% in the period 1979-1987.--Main operative risk factors are gallbladder and bile duct complications and the age beyond the 6th decade of life.--The lethality of choledocholithiasis actually amounts to the 37-fold of uncomplicated cholecystolithiasis and the lethality of all primary and secondary gallstone operations after the 6th decade of life amounts to the 38-fold in comparison with younger patients.--A further reduction of operative risk appears possible by reason: 1. Consequent early operation. 2. immediate operative or endoscopic removal of extrahepatic cholestasis, 3. complex intraoperative diagnostics of bile duct and papilla Vateri, 4. preoperative single dose AB prophylaxis or short-term therapy, 5. general low dose heparin prophylaxis, 6. primary endoscopic therapy in residual stones or irreversible stenosis of papilla Vateri and 7. interdisciplinary diagnosis and treatment of senile complications.

Aged↗
PubMed1988

Reconstitution of purified cardiac muscle calcium release channel (ryanodine receptor) in planar bilayers.

The purified ryanodine receptor of heart sarcoplasmic reticulum (SR) has been reconstituted into planar phospholipid bilayers and found to form Ca2+-specific channels. The channels are strongly activated by Ca2+ (10 nM) in the presence of ATP (1 mM) and ryanodine, and inactivated by Mg2+ (3 mM) or ruthenium red (30 microM). These characteristics are diagnostic of calcium release from heart SR. The cardiac ryanodine receptor, which has previously been identified as the foot structure, is now identified as the calcium release channel. A similar identity of the calcium release channel has recently been reported for skeletal muscle. The characteristics of the calcium release channel from skeletal muscle and heart are similar in that they: 1) consist of an oligomer of a single high molecular weight polypeptide (Mr 360,000 for skeletal muscle and 340,000 for heart); 2) exist morphologically as the foot structure; 3) are activated (ATP, Ca2+, ryanodine) and inhibited (ruthenium red and Mg2+) by a number of the same ligands. Important differences include: 1) Ca2+ activation at lower concentration of Ca2+ for the heart; 2) more dramatic stabilization by ryanodine of the open state for the skeletal muscle channel; and 3) different relative permeabilities (PCa/PK).

Adenosine Triphosphate↗
PubMed1988

Particle counting by fluorescence correlation spectroscopy. Simultaneous measurement of aggregation and diffusion of molecules in solutions and in membranes.

A method for simultaneous determination of molar weights (M) and lateral diffusion constants (D) of particles in three- and two-dimensional systems is described. Spontaneous concentration fluctuations in space and time are analyzed, by monitoring fluctuations in the fluorescence from fluorescein-labeled molecules (1 dye/molecule is sufficient), excited by a rotating laser spot. For particles in solution, M values are determined over the range of 3 x 10(2) to 3 x 10(11) daltons, and D values can be determined from approximately 10(-7) to 10(-10) cm2/s. The time for a determination is approximately 1 min. Aggregation can be followed by changes of either M or D. This method is used to study the calcium dependence of vesicle aggregation or fusion, and the time course of aggregate formation of porin (an Escherichia Coli outer membrane protein) in lipid monolayers. Essential parameters for the development of the method are described. Equations to estimate the signal-to-noise ratios and to find the optimal free parameters for a specific application are derived. The theoretical predictions for the correlation function of the signal and for the signal-to-noise ratio are compared with observed values.

Chemical Phenomena↗
PubMed1988

Purified skeletal muscle 1,4-dihydropyridine receptor forms phosphorylation-dependent oligomeric calcium channels in planar bilayers.

The purified 1,4-dihydropyridine receptor from skeletal muscle has been incorporated into planar bilayers, and its channel characteristics have been investigated. Conductances showed the characteristics of an L-type Ca2+ channel: divalent cation selectivity (PBa/PNa approximately equal to 30), blockage of Na+ conductance by micromolar Ca2+, and blockage of the Ca2+ channel by D890 and by Cd2+. The alpha 1 subunit of the receptor must be phosphorylated by the cAMP-dependent protein kinase to give channel activity. BAY K 8644 did not activate nonphosphorylated channels, and (+)-PN200-110 caused dramatic prolongation of mean open times when applied after phosphorylation. Channel properties were found to be dependent on association of receptor molecules in the bilayer. Single receptor molecules form channels of 0.9 pS (100 mM Ba2+) and show no voltage-dependent gating. Upon association, both voltage-dependent gating and higher conductance events are recovered; stabilized conductance levels assume values of even multiples of 0.9 pS, predominately 7.5 and 15 pS and multiples of these values up to 60 pS. Thus, individual channels become functionally coupled (synchronous opening and closing) with association, reinstating the characteristics of one larger unitary channel. It is concluded that the L-type Ca2+ channel represents an oligomer of 1,4-dihydropyridine-receptor protein complexes, each of which constitutes a channel, where the array of channels (oligochannel) opens and closes in concerted action.

Animals↗
PubMed1988

Purified ryanodine receptor of skeletal muscle sarcoplasmic reticulum forms Ca2+-activated oligomeric Ca2+ channels in planar bilayers.

The ryanodine receptor of sarcoplasmic reticulum (SR) from fast-twitch skeletal muscle has been purified and found by electron microscopy to be equivalent to the feet structures that are involved in situ in the junctional association of transverse tubules with terminal cisternae of SR. We now find that when the purified receptor is incorporated into vesicle-derived planar bilayers, it forms Ca2+-specific channels, which are dependent on submicromolar Ca2+ for activity. In the presence of 1 mM ATP, the channel shows essentially no activity at 10 nM Ca2+ but becomes highly activated at 50 nM Ca2+. At suboptimal Ca2+ levels (100 nM), the channel is strongly activated by 1 mM ATP and can be blocked by ruthenium red, both effects being prevented by higher Ca2+ levels (1 microM). Mg2+, added from the cis side at millimolar concentrations, blocks Ca2+ flux through the channel from trans to cis (equivalent to flux from luminal to myoplasmic compartment). Ryanodine stabilizes the open state of the channel and blocks the action of ruthenium red to close the channel. Thus, the purified ryanodine receptor incorporated into a bilayer has the Ca2+-channel characteristics consistent with the calcium release observed in isolated terminal cisternae vesicles. Furthermore, ryanodine induced the appearance of a sublevel gating mode characterized by long open conductance states, which were integral multiples of the smallest observed conductance, 3.8 pS in 50 mM Ca2+. The purified receptor consists essentially of a single-sized high molecular weight polypeptide (Mr. approximately equal to 360,000), which on reconstitution forms the square rectangles diagnostic of the feet structures. We conclude that the identity of the Ca2+-release channel of SR is the foot structure, which consists of an oligomer of the high molecular weight polypeptide.

Adenosine Triphosphate↗
PubMed1987

[A new catheter for hemodynamic studies].

It is reported on a new catheter technique for the determination of the cardiac output by means of the method of thermodilution. It consists of a thin sensorcatheter (3 Ch), which contains a microthermistor as temperature sensor and additionally two electrodes. The insertion of the catheter is carried out via puncture of the subclavian vein by means of a special introducer set, the outer sheath of which can used for injecting the cold solution. The positioning of the sensor catheter into the pulmonary artery may be done by intracardiac ECG monitoring with the help of the two electrodes. By means of these electrodes, however, also an electric stimulation of the right ventricle is possible, so that, for instance, haemodynamic investigations depending on stimulation parameters can be performed by only one catheter. The clinical test of the new catheter-set was very successful.

Cardiac Catheterization↗