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Biomedical subjects

J W Trank

Publications and source records attributed to J W Trank.

14 recordsLinked to original sources
PubMed1989

Intracellular magnesium affects I(K) in single frog atrial cells.

Voltage-clamp experiments on single frog (Rana pipiens) atrial cells using whole cell recording techniques revealed that the addition of MgCl2 to the 150 mM KCl patch pipette solution influenced the voltage- and time-dependent potassium current (IK). After rupture of the membrane patch under the tip of the pipette, IK increased with time when the pipette solution was magnesium free, but decreased slightly when the solution contained 1.5 mM MgCl2. More dramatic decreases in IK occurred when the solution contained 3.0 or 10 mM MgCl2. In addition to suppressing the magnitude of IK, the activation rate of this current was enhanced by 10 mM MgCl2 but was not affected by 1.5 or 3 mM MgCl2. Other chloride salts containing mono-, di-, or trivalent cations were used to demonstrate that the effects of MgCl2 on IK were not related to alterations in ionic strength, osmolality, or chloride concentration produced by adding MgCl2 to the pipette solution. Our results suggest that changes in the intracellular magnesium concentration influence IK as the pipette solution exchanges with the intracellular fluid.

Animals↗
PubMed1986

Voltage-tension relations in single frog atrial cardiac cells.

Voltage-clamp experiments were performed on isolated single frog (Rana catesbeiana or Rana pipiens) atrial cells to determine the voltage-contraction relations of the single cardiac cell. The contractile responses of the single cell associated with long duration (3 second) depolarizing steps consisted of a rise to peak (phasic) followed by a decay to a sustained contraction (tonic). These phasic-tonic type contractile responses could be obtained under conditions where membrane potential was well controlled along the entire length of the cell. Thus, the data obtained on the single cell indicate that the phasic-tonic contractile response is the characteristic contractile response of frog atrial tissue. The voltage dependence of the extent of relaxation to the tonic component following the peak of the contraction was affected dramatically by the intracellular sodium concentration. This result indicates that both the relaxation following peak contraction as well as the tonic contraction are related to calcium control via the sodium-calcium exchanger. The data also indicate that calcium entry via the inward calcium current is required for the contractile response to have a phasic component. These data indicate that calcium entry via the inward calcium current followed by the sodium-calcium exchanger first reducing and then maintaining the intracellular calcium level produces the characteristic phasic-tonic contractile response.

Animals↗
PubMed1985

Implementation of a movement paradigm using the Commodore 64 microcomputer.

Implementation of an alternating movement paradigm for monkeys was achieved using an inexpensive but versatile microcomputer, the Commodore 64. During task performance, the computer monitors one of three user selectable input signals (e.g. joint position) and continuously displays this signal as a moving cursor on a video monitor along with a user positioned target box. Other user defined parameters include in-target holding time and reinforcement ratio. The system also provides two sound cues to signal entry of the cursor into the target box and successful completion of a trial. Extensive use is made of the computer's intrinsic hardware features for implementation of movement paradigm functions. Use of external components is limited to digitizing and interface hardware. A two part software package consisting of a BASIC and a machine language program performs all task and hardware related functions. Acquisition and display of analog input signals, display of target positions, and delivery of auditory cues and applesauce rewards are all controlled by the machine language program. All user defined parameters are specified from the BASIC menu program. The specific programs described in this paper should be applicable to the control of tasks requiring alternation of a behavioral parameter between two target zones.

Animals↗
PubMed1984

Depression of contractility following stretches and releases applied during contraction to single frog atrial cardiac cells.

The effects of stretches and releases on the contractile performance of isolated single frog atrial cells (Rana catesbeiana) were investigated. A stretch or release was imposed on the cell--either during a contraction (test) or before the onset of contraction (control)--and the contractile performance (length, velocity and force) of the test contraction was compared with that of the control contraction to determine whether the stretch or release imposed on the contracting cell altered the contractility of the cell. We found that the velocity of cell (and sarcomere) shortening for the remainder of the test contraction following either a stretch or release was markedly less than that occurring at the same time in the control contraction. This decreased velocity occurred even though the force in the test contraction was less than that in the control contraction and the sarcomere length was longer in the test contraction than in the control contraction. These results indicate that after a stretch or release imposed on the contracting cell, the force-velocity relationship at any given length and time is depressed than had the stretch or release not been imposed on the contracting cell. Thus, stretches and releases applied to the contracting single cardiac cell either produce a long-term depression in the contractility of the cell, or that the contractility at any given time and sarcomere length depends markedly on the history of the contraction.

Animals↗
PubMed1983

Arterial baroreceptor reflex control of heart rate in two species of turtle.

Attempts were made to stimulate an arterial baroreceptor reflex in anesthetized and conscious pond turtles. In turtles anesthetized with either alpha-chloralose or pentobarbital, occlusion of the ascending or descending aortas produced no reflex heart rate (HR) changes. In pentobarbital-anesthetized turtles, direct electrical or mechanical stimulation of potential baroreceptor sites along the central aortic arches and carotid arteries produced no significant changes in either HR or blood pressure (BP). Occlusion of the common carotid arteries also produced no HR or BP changes. Intravenously administered nitroglycerin lowered BP but caused no reflex tachycardia in anesthetized turtles. Phenylephrine and angiotensin elevated BP in the anesthetized turtle but caused no reflex bradycardia. In conscious turtles phenylephrine increased BP and nitroglycerin decreased BP. Neither response produced a statistically significant HR change, although HR tended to decrease transiently with phenylephrine and increase with nitroglycerin. These HR changes were abolished by atropine. Rapid intra-arterial infusion of 6% dextran transiently raised BP but caused no reflex bradycardia. These experiments suggest that cardiovascular regulation in the turtle is accomplished without a major contribution from arterial baroreceptor reflexes.

Anesthesia, General↗
PubMed1983

Effect of external force on relaxation kinetics in single frog atrial cardiac cells.

The effects of external force on relaxation kinetics were investigated in isolated single frog (Rana catesbeiana) atrial cells. We found that force decay occurred at a maximum and constant rate for a significant portion of auxotonic relaxation, and this rate was linearly related to the peak force developed during auxotonic contraction. The slope of the linear relationship between the maximum rate of auxotonic force decay and peak auxotonic force was not affected by changes in the level of contractile activation produced by activating the cell with different stimulus durations. The rate of force change during auxotonic contraction and relaxation in the isolated cell is directly related to the average sarcomere velocity within the cell. Thus, the results indicate that during auxotonic relaxation the velocity of sarcomere extension is directly related to the peak auxotonic force, and sarcomere extension, during relaxation, is therefore affected by external force. The direct effect of external force on relaxation kinetics was confirmed by the observation that force changes imposed on the cell during relaxation immediately altered the velocity of the extending cell from any given length. However, data are also presented which demonstrate that rapid sarcomere extension occurs during relaxation under conditions where external forces are negligible. Thus, rapid sarcomere extension during relaxation does not require large external forces, and internal forces must play a role in sarcomere extension during relaxation. An explanation is given for these apparently contradictory results.

Animals↗
PubMed1979

Sarcomere length-resting tension relation in single frog atrial cardiac cells.

It generally has been thought that the relatively high resting tension characteristic of cardiac tissue resides in structures (collagen, elastin) external to the individual cardiac cells, but the evidence to support this conclusion has been indirect, since the resting tension of intact single cardiac cells has not been determined previously. The purpose of the present investigation was to determine the resting tension (stress)-sarcomere length relationships of single intact frog atrial cells. For tension determinations, a single cell was attached between two poly-L-lysine coated glass beams; one beam served as a compliant calibrated cantilevered force beam, and length changes were imposed on the cell by movement of the other beam. Coventional bright-field light microscope techniques were used to view the cell, the sarcomere pattern within the cell, and the position of the force beam. The resting tension of the intact cell increased from a value of about 10 nN at a sarcomere length of 2.35 microns to a value of about 130 nN at a sarcomere length of 3.45 microns. Lagrangian and Eulerian resting stress-sarcomere length relationships were computed from the resting tension-sarcomere length relationships. The Lagrangian stress increased from a value of about 0.6 mN/mm2 at a sarcomere length of 2.35 microns to a value of about 7 mN/mm2 at a sarcomere length of 3.45 microns. These values of stress are about 8- to 30-fold less than those previously reported for intact frog atrial tissue and indicate that the resting tension of intact frog atrial preparations resides primarily in structures external to the individual cardiac cell.

Animals↗
PubMed1976

Preparation of isolated single cardiac cells from adult frog atrial tissue.

Isolated cardiac cells from bullfrog atrial tissue can be readily prepared by digestion of intact fragments of atrial tissue with trypsin and collagenase. These isolated cells have dimensions of about 5 mum in width and range in length from 300 mum to over 500 mum. Such isolated cells may prove useful for the investigation of contractile activity of cardiac muscle at the single cell level and at the sarcomere level within the single cell.

Animals↗
PubMed1976

Limitations of the double sucrose gap voltage clamp technique in tension-voltage determinations on frog atrial muscle.

The purpose of this study was to evaluate the limitations of the double sucrose gap voltage clamp technique in the determination of tension-voltage relationships for frog atrial muscle. Tension-voltage relationships were determined under two conditions. In one case we determined both the tension response and slow inward current associated with an apparent step depolarization (step-clamp) as a function of the magnitude of the step depolarization. In the second case, an action potential was elicited, the voltage clamp was applied early during the plateau phase of the action potential, and the tension response was determined as a function of the clamp potential (action potential-clamp). Under both step-clamp and action potential-clamp conditions, the waveform of the tension response rose to a peak value (Tp) and then decayed with time to a tension that was maintained for the duration of the depolarization. The Tp-clamp potential relationships obtained under step-clamp and action potential-clamp conditions were similar. Microelectrode measurements of transmembrane potential of cells in the "voltage-clamped" region of the preparation demonstrated the lack of temporal and spatial voltage control under both step-clamp and action potential-clamp conditions, and also demonstrated that acquisition of spatial voltage control occurred at about the same time that the tension response reached its peak value. These data indicate that this voltage clamp technique does not allow an accurate determination of the so-called phasic tension-voltage relationship in frog atrial muscle because of a lack of temporal and spatial control of voltage during the rising phase of the tension response.

Action Potentials↗
PubMed1974

An assessment of the double sucrose-gap voltage clamp technique as applied to frog atrial muscle.

The homogeneity of voltage clamp control in small bundles of frog atrial tissue under double sucrose-gap voltage clamp conditions was assessed by intracellular microelectrode potential measurements from cells in the test node region. The microelectrode potential measurements demonstrated that (1) good voltage control of the impaled cell existed in the absence of the excitatory inward currents (e.g., during small depolarizing clamp pulses of 10-15 mV), (2) voltage control of the impaled cell was lost during either the fast or slow excitatory inward currents, and (3) voltage control of the impaled cell was regained following the inward excitatory currents. Under nonvoltage clamp conditions the transgap recorded action potential had a magnitude and waveform similar to the intracellular microelectrode recorded action potentials from cells in the test node. Transgap impedance measured with a sine-wave voltage of 1,000 Hz was about 63% of that measured either by a sine-wave voltage of 10 Hz or by an action potential method used to determine the longitudinal resistance through the sucrose-gap region. The action potential data in conjunction with the impedance data indicate that the extracellular resistance (R(s)) through the sucrose gap is very large with respect to the longitudinal intracellular resistance (R(i)); the frequency dependence of the transgap impedance suggests that at least part of the intracellular resistance is paralleled by a capacitance. The severe loss of spatial voltage control during the excitatory inward current raises serious doubts concerning the use of the double sucrose-gap technique to voltage clamp frog atrial muscle.

Action Potentials↗