Equivalent Circuit of Frog Atrial Tissue as Determined by Voltage Clamp-Unclamp Experiments

Tarr, Merrill; Trank, J W

doi:10.1085/jgp.58.5.511

Cited by 36 publications

(29 citation statements)

References 10 publications

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“…The rapid jumps on the electrode trace during the on and off of the current transients were not present in the optical trace. The rapid jump in the intracellular recordings observed during the passage of current is caused by a voltage drop across the extracellular resistance in series with the membrane resistance (Beeler & Reuter, 1970;Tarr & Trank, 1971;Goldman & Morad, 1977). That the optical signal does not detect this extracellular voltage component suggests that the dye molecules respond only to the transmembrane potential rather than to the potential changes in the extracellular clefts.…”

Section: Resultsmentioning

confidence: 99%

Optical probes of membrane potential in heart muscle.

Morad¹,

Salama²

1979

The Journal of Physiology

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SUMMARY1. The fluorescent dye Merocyanine-540 and the two weakly fluorescent dyes Merocyanine-rhodanine and Merocyanine-oxazolone are shown to respond as optical probes of membrane potential in heart muscle.2. In frog hearts stained with Merocyanine-540, the absorption at 540 nm decreases by 0-1-1.0% and increases at 570nm by 0.01-0.5% during the action potential. With either a 540 or a 570 nm excitation wave-length, the fluorescence increases by 1-2 %. The time course of all three optical measurements follows the kinetics of the action potential. 3. Merocyanine-rhodanine exhibits potential-dependent optical responses through a 0-5 % decrease in absorption at 750 nm, and Merocyanine-oxazolone has a 1I0 % decrease in absorption at 720 nm. Their optical responses have a signal-to-noise ratio of 100/1 and 500/1, respectively. 4. The action spectrum of Merocyanine-rhodanine is triphasic in frog heart with an increase in transmittance from 780 to 700, a decrease from 700 to 600, and an increase from 600 to 450 nm. Merocyanine-oxazolone shows only increases in transmittance during membrane depolarization.5. The optical responses of these probes are linear with respect to changes in membrane potential.6. Pharmacological agents or ionic interventions do not alter the membrane potential sensitivity of 7. Rapid spectrophotometric measurements at various phases of the action potential indicate that the potential dependent optical signals of Merocyanine-540 are produced by changes in amplitude of fluorescence and absorption bands. The lack of wave-length displacement as a function of membrane potential, i.e. electrochromism, is not the mechanism governing the voltage sensitivity of Merocyanine-540.8. The data suggest that these Merocyanine dyes bind to the plasma membrane and serve as linear optical probes of membrane potential in heart muscle.

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Section: Resultsmentioning

confidence: 99%

Optical probes of membrane potential in heart muscle.

Morad¹,

Salama²

1979

The Journal of Physiology

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“…From this we expect the slow components of membrane current to be measured without appreciable error whereas the record of fast inward current may be subject to some distortion (cf. Tarr & Trank, 1971 In the sucrose gap arrangement of Fig. 1, mechanical activity, like electrical activity, was restricted to the central portion of the preparation.…”

Section: Methodsmentioning

confidence: 95%

Membrane current and contraction in frog atrial fibres

Einwächter¹,

Haas²,

Kern³

1972

The Journal of Physiology

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SUMMARY1. Membrane current and mechanical activity were recorded from short segments of frog atrial muscle strips using a double sucrose gap voltage clamp arrangement. Experiments were performed at 4-7O C. Two types of contraction were observed dependent upon the duration of the clamp.2. Short-lasting depolarizations caused a flow of Ca inward current, ICa, and development of a phasic contraction. Time to peak tension approximated 400 msec. Both ICa and contraction, as functions of membrane potential, had a threshold of about -40 mV and were maximal at inside positive potentials in normal Ringer fluid. Peak tension decreased at strong depolarizations. 3. The minimum time of depolarization required for initiation of a phasic contraction was 40-70 msec. The time necessary for full activation of contraction was 200-300 msec and comparable to the period of time covered by the flow of ICa-4. There was no marked change in peak tension upon repetitive depolarization to the same membrane potential.5. Restoration of (phasic) contractility after a preceding contraction was strongly dependent on the level of membrane potential between conditioning and test pulse. Restoration was half complete at potentials around -45 mV.6. Long-lasting depolarizations generated tonic (sustained) contractions superimposed on the phasic (transient) ones. Threshold potential for initiation of tonic contractions was usually positive to the threshold of phasic contractions. The time taken to attain the final level of tension ranged between 0 7 and 3 sec. Plateau tension, as a function of membrane potential, increased with increasing depolarization and reached a flat maximum at about + 50 mV in normal Ringer fluid. 7. At membrane potentials near zero level, plateau tension developed by the tonic mechanism was about twice peak tension due to phasic contraction.

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“…It has been reported previously that the capacitive current decayed with a single exponential in dog ventricular fibres (r = 1-3 msec, Beeler & Reuter, 1970a), in cat ventricular fibres (T = 02-2 msec, New & Trautwein, 1972a), and in sheep or calf ventricular fibres (T = 5.4 msec, McGuigan, 1974). It seems likely that this reflects measurement errors rather than tissue or experimental differences and a more detailed look at capacitive currents in sheep or calf preparations has in fact indicated the presence of two Rougier et al (1968) and Tarr & Trank (1971) among others have reported capacitive currents decaying mono-exponentially while a recent detailed study (Connor, Barr & Jakobsson, 1975) indicates the presence of one to three components. Although other interpretations are possible (see Connor et al 1975), the slow capacitive phase may well reflect the discharge of some capacity in the sucrose region (McGuigan, 1974).…”

Section: Methodsmentioning

confidence: 99%