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Biomedical subjects

M Hencek

Publications and source records attributed to M Hencek.

16 recordsLinked to original sources
PubMed1990

Effects of ruthenium red on excitation and contraction in muscle fibres with Ca2+ electrogenesis.

The effect of ruthenium red (RR) on the electrical and contractile responses, membrane Ca currents, staining patterns of the external and internal membrane system were tested in intact and mechanically skinned muscle fibres of the crayfish Astacus fluviatilis. The following results were obtained: 1. Depression of the contractile responses following membrane depolarization (twitch, tetanus, potassium contractures). 2. Caffeine contractures were unaffected in intact (100 mumol/l - 1 mmol/l RR) and blocked in skinned fibres (30 mumol/l RR). 3. Mechanical threshold and mechanical latency were increased and/or prolonged. 4. The rate of depolarization of the action potentials (AP) was decreased and decremental spread of AP was recorded. 5. Both fast and slowly inactivating Ca ionic currents were decreased and the time constants of activation (tau(m] and inactivation (tau(h] were prolonged after RR (100 mumol/l) pretreatment. 6. The penetration of RR into the T-system was inversely related to its binding to the sarcolemma. The depression of depolarization-induced contractions was most pronounced in fibres with unstained sarcolemma and stained T-tubules. In intact fibres, neither terminal cisternae nor other elements of SR were stained. On the contrary, all internal membrane structures were stained in skinned fibres. There was a gradient of staining intensity from surface toward the interior.

Animals↗
PubMed1990

[Excitation-contraction coupling in isolated muscle fibers with calcium electrogenesis preserved in a culture medium].

The aim of the present work was to check changes in functional characteristics of isolated muscle cells, operating on the calcium electrogenesis principle, while kept in culture media for several days. Skeletal muscle cells of the crayfish Astacus fluviatilis were used to study potassium/caffeine contractures and single/tetanic contractions; simultaneous electrical and mechanical responses were recorded by the microelectrode technique, and kinetics of calcium ionic currents was studied under vaseline-gap voltage clamp. In cultured fibers, active membrane responses and calcium current kinetics remained unchanged, or slightly increased, whereas contractile responses were substantially reduced. A gradual excitation-contraction decoupling was observed. The fiber maintained the ability to respond to direct activation (by caffeine) of the contractile apparatus. Subthreshold caffeine concentrations (0.2-0.5 mmol/l) and adrenaline (6.0(-6), 6.10(-5) mol/l) enhanced the inhibited (due to the culturing) single contractile responses.

Action Potentials↗
PubMed1989

Calcium channels in skeletal muscle fibres of the frog.

The vaseline gap voltage clamp technique was used to study slow and fast calcium currents in phasic and tonic muscle fibres of the frogs Rana temporaria (R.t.) and Xenopus laevis (X.l.). At physiological Ca2+ and Na+ concentrations three inward currents could be recorded in R.t. twitch muscle fibres: a fast Ca current, a slow Ca current, and a non-specific (INS) current carried by Na ions. The last current appeared as a sole component at a low threshold membrane potential (MP -55 mV) and was present until the slow Ca current appeared. In tonic R.t. muscle and twitch X. laevis fibres only the fast and the slow Ca currents could be recorded; however the inactivation of the slow Ca current was very prolonged in the presence of Na ions. A modulatory effect of Na ions on Ca2+ currents was observed. In phasic fibres the fast Ca currents inactivated either very slowly or rapidly.

Animals↗
PubMed1978

Operational amplifier with adjustable frequency response.

The authors describe an operational amplifier with an adjustable frequency response and its use in membrane physiology, using the voltage clamp and current clamp method. The amplifier eliminates feedback poles causing oscillation. It consists of a follower with a high input resistance in the form of a tube and of an actual amplifier with an adjustable frequency response allowing the abolition of clicks by one pole and of oscillation by two poles in the 500 Hz divided by infinity range. Further properties of the amplifier: a long-term voltage drift of 1 mv, a temperature voltage drift of 0.5 mv/degrees K, input resistance greater than 1 GOhm, amplification greater than 80 dB, output +/- 12 v, 25 ma, noise, measured from the width of the oscilloscope track in the presence of a ray of normal brightness, not exceeding 50 muv in the 0-250 kHz band, f1 = 1 MHz. A short report on the amplifier was published a few years ago (Gulísek and Hencek 1973).

Amplifiers, Electronic↗
PubMed1978

Membrane currents in a calcium type muscle membrane under voltage clamp.

Four ionic current components were identified in the total membrane current recorded under voltage clamp conditions from the muscle membrane of the crayfish (Astacus fluviatilis). The early inward current component is dependent on the presence of Ca2+ ions, disappears in Ca2+ free solutions and is insensitive to variaton of external Na+ ions and to tetrodotoxin. The outward current consists of at least three components, an early, a late and a slow outward current. The outward currents are sensitive to TEA and their reversal potentials differ. The early potassium current may be separated in a proportion of fibres by a hump from the later potassium current. An insufficient space clamp as a cause of the hump was excluded by comparing the size of the clamped membrane area with the distribution of large membrane clefts in the fibre. The early outward current is critically dependent on the presence of Ca2+ ions and is relatively more sensitive to TEA ions and to conditioning depolarisation than the late outward current.

Action Potentials↗
PubMed1977

Calcium currents and conductances in the msucle membrane of the crayfish.

1. Membrane currents in calcium type muscle membrane of the cray-fish Astacus fluviatilis were analysed by a method in which a membrane microarea was isolated by circulating sucrose rings contacting the fibre perpendicular to the fibre surface.2. The early calcium inward currents were separated from the total membrane currents by subtraction of the early and delayed potassium currents from the total membrane current.3. The isolated calcium currents show a time course characteristic for a transient change of calcium conductance. The presence of inactivation was further checked by the time course of the tail currents at the end of voltage clamp pulses of variable duration.4. The reversal potential of the early calcium currents determined from the current-voltage relations was +85 +/- 4.2 mV. The calcium potentials were used to express the calcium currents in the form of chord conductances.5. Calcium conductances (g(Ca)) as functions of time and voltage were found to be described quantitatively on the assumption that g(Ca) is determined by two variables (m and h), according to the equation g(Ca) = m(6)hg(Ca), where g(Ca) is a constant and m and h obey first order differential equations of the Hodgkin-Huxley type.6. The activation parameters of the g(Ca) were determined by fitting the solutions of the above equations to the experimental values of the g(Ca). This method was also used to check the inactivation parameters.7. The inactivation parameters of the g(Ca) were obtained from the inactivation curves, which were determined for several membrane potentials by variation of the duration of the conditioning step.8. The average calcium conductance constants were tabulated and compared with sodium conductance constants in excitable membranes.

Animals↗