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F Sachs

Publications and source records attributed to F Sachs.

At least 73 records · Page 4Linked to original sources
PubMed1990

Characterization of stretch-activated ion channels in Xenopus oocytes.

1. The gating and permeation properties of endogenous stretch-activated (SA) ion channels in Xenopus oocytes have been studied using the patch-clamp single channel recording technique. 2. As estimated from the probability of being open (Po), SA channels were equally sensitive to suction or pressure. The Po was also weakly sensitive to voltage, increasing with depolarization. Channel activation did not require Ca2+. 3. Kinetic analysis of single-channel records indicated that there are three closed states and one open state. Among three closed-time distributions, the longest was the most sensitive to both pipette pressure and membrane voltage. The open time was independent of both pressure and voltage under a wide variety of ionic conditions, but was sensitive to the species of extracellular ion as follows: Na+ greater than Cs+ greater than K+ greater than Rb+ greater than Li+. The open time had a monotonic mole fraction relationship in mixtures of Li+ and K+. 4. The SA channels were cation-selective inward rectifiers. The selectivity for permeation, based on slope conductance, was: K+ greater than NH4+ greater than Cs+ greater than Rb+ greater than Na+ greater than Li+ greater than Ca2+. 5. Tetraethylammonium (TEA+) was impermeable but was not a channel blocker. 6.Open-channel current amplitude saturated with increasing extracellular K+, and was a monotonic function of the mole fraction of Li+ and K+ in mixtures of the two ions. 7. The channel has at least two separate ion binding sites: an intra-channel site suggested by the permeation data, and an allosteric site suggested by the voltage-independent effects of permeant ions on open time. A symmetric two-barrier, one-site model can quantitatively describe the permeation data. A kinetic model is proposed to quantify the gating kinetics and the effect of ion binding at the allosteric site.

Action Potentials↗
PubMed1989

Block of stretch-activated ion channels in Xenopus oocytes by gadolinium and calcium ions.

Gadolinium ions produce three distinct kinds of block of the stretch-activated (SA) ion channels in Xenopus oocytes: a concentration-dependent reduction in channel open time, a concentration-dependent reduction in open channel current, and a unique, steeply concentration-dependent, reversible inhibition of channel opening. This last effect reduces the probability of a channel being open from about 10(-1) at 5 microM to less than 10(-5) at 10 microM gadolinium. Calcium has effects on open time and current similar to that of gadolinium, but this channel is permeable to calcium and calcium does not completely inhibit channel activity. The availability of a blocker for SA ion channels may help to define their physiological function, and will simplify the use of oocytes as an expression system for ion channels.

Animals↗
PubMed1989

Improving performance of motorized slides for micromanipulation.

Motorized linear slides used as micromanipulators for biological use suffer from 3 problems: vibration at low speed, poor ergonomic design of the controller and slow coarse positioning. These problems are not hard to solve by minor modifications to the controller and the slides.

Electrophysiology↗
PubMed1988

Mechanical transduction in biological systems.

Mechanical transduction, the transformation of cellular deformation into an electrochemical response, is essential to the survival of both cells and higher organisms. In the specialized sensory organs, mechanotransducers are responsible for the sensations of hearing, touch and vibration, local gravity, kinesthesis, and probably osmoreception. In the viscera, mechanoreception provides sensory feedback on organ volume and pressure. At the cellular level, mechanoreceptors are known to provide feedback for avoidance reactions in free-swimming protozoans and for the gravitational and tactile reactions of plants. Mechanotransducers are probably essential in regulating cell volume and cell division. The known properties of mechanotransducers can be accounted for by ion channels whose gating is controlled by membrane strain.

Animals↗
PubMed1987

Baroreceptor mechanisms at the cellular level.

Nothing is known of transduction mechanisms of baroreceptors in vivo. Not even the site of transduction is known. However, there are mechanotransducer ion channels that provide a useful model system of transduction. In these channels, transduction is accomplished by a strain-dependent increase in the probability of being open. Membrane tension is coupled to the channel by cytoskeletal strands that concentrate the strain energy from a large (approximately equal to 4000 A diameter) area of membrane and thereby provide high sensitivity. The channel is fast and does not inactivate, but viscoelastic coupling to the channel can dramatically alter the transfer function.

Animals↗
PubMed1986

Biophysics of mechanoreception.

Several types of cells' skeletal, muscle, nerve, epithelia, and heart have been shown to contain ion channels which are sensitive to membrane tension. In chick skeletal muscle, the transduction persists in excised patches and involves no chemical messengers. Quantitative analysis of single channel records reveals that the sensitivity to stretch can be described by a linear four state model with three closed (C) and one open (O) state: (Formula: see text). Only the rate constant k12 is sensitive to tension (and membrane potential) following the law: k12 = kO12 exp/(theta T2 + alpha V) where theta is a constant describing the sensitivity to tension, T, and alpha is a constant describing the sensitivity to voltage, V, and kO12 is a constant. The form of the tension sensitivity can be accounted for by a model in which strain energy is used to gate the channel. Analysis of strain sensitivity, theta, indicates that the channel must concentrate energy from a large (ca. 500-nm diameter) area of membrane which suggests that the channel is in series with a component of the cytoskeleton. Treatment with cytochalasins suggests that actin is mechanically in parallel with the channel. When a channel with the above properties is incorporated into a simple model of mechanical transduction in hair cells, the resulting model is capable of explaining the kinetic features and the sensitivity found in the cochlear-vestibular system. The proposed gating mechanism of mechanical transduction appears to be general and can account for existing data on a variety of systems.

Animals↗
PubMed1985

Mechanotransducer ion channels in chick skeletal muscle: the effects of extracellular pH.

The membrane of tissue-cultured chick pectoral muscle contains an ionic channel which is activated by membrane tension. With 150 mM-external K+ and 150 mM-internal Na+, the channel has a conductance of 70 pS and a reversal potential of +30 mV. With 150 mM-external Na+ and 150 mM-internal K+ (normal gradient) the channel has a conductance of 35 pS and a reversal potential of -30 mV. The ratio of K+ permeability to Na+ permeability, PK:PNa, is 4 based upon reversal potentials and is 2 based upon conductance. Kinetic analysis of single-channel records indicates that there are one open (O) and three closed (C) states. When analysed according to a linear sequential model: C1-C2-C3-O4, only the rate constant that governs the C1-C2 transition (k1,2) is found to be affected by stretch or voltage. The effects of stretch and voltage on k1,2 can be summarized as k1,2 = k1,2(0) exp (alpha V + theta P2), where K1,2(0) is the voltage and stretch-independent part of the rate constant, alpha is the voltage sensitivity, V is the transmembrane potential, theta is the stretch sensitivity and P is the applied suction. Increasing extracellular pH from 7.4 to 10.0 increases both alpha and theta in a manner suggesting titration of site(s) with a pK of 9.1. A single lysine of N-terminal amino acid may be be responsible for modulating both the voltage and pressure responses. Extracellular pH does not affect k1,2(0), the voltage- and stretch-independent part of k1,2, suggesting that pH in the range 7.4-10 does not alter the local surface charge. The conductance and reversal potential of the s.a. channel are unaffected by pH, suggesting that the titrated site(s) is not close to the mouth of the channel.

Action Potentials↗
PubMed1984

Single-channel currents from acetylcholine receptors in embryonic chick muscle. Kinetic and conductance properties of gaps within bursts.

In tissue-cultured chick muscle, bursts of current from single nicotinic ion channels contain a variety of low-conductance gaps. One population has a lifetime of approximately 0.1 ms and an unknown conductance. A second population has a lifetime of 2-10 ms and conductance of zero. The third population has a lifetime of 0.5-1 ms and a mean conductance approximately 2% that of the main conductance state. This subconductance state has an agonist-dependent lifetime, longer for suberyldicholine than for acetylcholine, and is liganded to the same extent as the main conductance state. Subconductance gaps have a linear current-voltage behavior in the range -60 to -140 mV and appear to have the same reversal potential as the main state. The subconductance state is composed of a group of states which interconvert with correlation times longer than 300 microseconds.

Animals↗
PubMed1984

Stretch-activated single ion channel currents in tissue-cultured embryonic chick skeletal muscle.

The membrane of tissue-cultured chick pectoral muscle contains an ionic channel which is activated by membrane stretch. Nicotinic channels and Ca2+-activated K+ channels are not affected by stretch. In 150 mM-external K+ and 150 mM-internal Na+ the channel has a conductance of 70 pS, linear current-voltage relationship between -50 and -140 mV and a reversal potential of +30 mV. Kinetic analysis of single-channel records indicates that there are one open (O) and three closed (C) states. The data can be fitted by the reaction scheme: C1-C2-C3-O. Only the rate constant that governs the C1-C2 transition (k1,2) is stretch-sensitive. None of the rates are voltage-sensitive. The rate constant k1,2 varies with the square of the tension as k1, 2 = k0 X e alpha T2, where alpha is a constant describing the sensitivity to stretch and T is the tension. A typical value of alpha is 0.08 (dyn cm-1)-2. Following exposure to cytochalasin B the channel becomes more sensitive to stretch. The stretch-sensitivity constant, alpha, increases from 0.08 to 2.4 (dyn cm-1)-2. The probability of the channel being open is strongly dependent upon the extracellular K+ concentration. With a suction of 2 cmHg the probability increases from 0.004 in normal saline (5 mM-K+) to 0.26 in 150 mM-K+. The channel appears to gather force from a large area of membrane (greater than 3 X 10(5) A2), probably by a cytochalasin-resistant cytoskeletal network.

Action Potentials↗
PubMed1983

Flickering of a nicotinic ion channel to a subconductance state.

Nicotinic acetylcholine channels show bursts of activity where open channel currents are separated from each other by short closed periods called flickers. These flickers presumably represent transitions from the open state to the state preceding the first opening of a burst (doubly liganded, closed state). Using tissue cultured chick pectoral muscle, we have examined the amplitude distribution of flickers. Of those events sufficiently long to permit accurate measurement of the amplitude (approximately 25% of all flickers), approximately two-thirds had a mean current equal to 10% of the fully open channel. The remaining one-third did appear to close completely. The subconducting flicker state is not a requisite step preceding channel opening. We conclude that there are three types of flicker events: a short event (time constant approximately 0.1 ms) whose current distribution is uncertain and two longer events (time constant approximately 1 ms), one of which has a current approximately 10% of the main open state and the other of which has a current indistinguishable from zero. In contrast, the amplitude of flickers induced by the local anesthetic QX-222 is indistinguishable from zero.

Animals↗
PubMed1983

Single-channel electrophysiology: use of the patch clamp.

The patch clamp technique affords unparalleled resolution of the detailed properties of ion channel currents. Patch clamping is not difficult and has been used to record single-channel currents from many cell types. The number of artifacts associated with the method appears to be rather small. The main experimental difficulties arise from the need to process large amounts of data. With the development of inexpensive computers and mass storage devices, these problems should be alleviated. The study of membrane excitability is expanding rapidly owing to the introduction of high-resolution patch clamp techniques. The conceptual revolution that will inevitably follow is just beginning.

Animals↗
PubMed1982

The automated analysis of data from single ionic channels.

The development of single channel recording has brought with it the need to analyse enormous amounts of data. The data analysis is time consuming and subject to observer biases since the events are random in time and are contaminated with uncorrelated noise. We have developed a heuristic pattern recognition program which identifies with high precision single channel currents and rejects contaminating noise. The program interactively provides for a variety of amplitude and duration measures. Analysis is flexible and rapid: a file containing over 10,000 events can be analysed in under 2 h. Specific detection features include variable lowpass filtering, automatic baseline restoration, and adaptive amplitude thresholds. A record is analysed through duration histograms, binomial estimates of the number of active channels present, cross-correlation estimates between parameters, spectral analysis of events and background noise, and stationarity of mean channel current. The graphic output facilities can plot raw data (after filtering and baseline restoration) with the idealized signal superimposed or with detected events underlined. A batch processing facility has been included to allow processing of data during periods of low computer demand.

Animals↗