The Role of Intracellular Sodium in the Control of Cardiac Contraction<sup><i>a</i></sup>

Lee, Chin O.; Levi, Allan J.

doi:10.1111/j.1749-6632.1991.tb17329.x

Cited by 26 publications

(5 citation statements)

References 22 publications

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“…The apparatus used for fluorescence measurement has been described previously [23]. The wheel (Cairn Research) carrying the 340 and 380 nm filters was rotated at 165 Hz to improve time resolution of the Fura-2 signal (this gave one Fura-2 ratio measurement every 6 ms).…”

Section: Fluorescence Measurementmentioning

confidence: 99%

Voltage dependence of the Fura-2 transient in rabbit left atrial myocytes at 37°C

Mitcheson

Hancox

Levi

1997

Pfl�gers Archiv European Journal of Physiology

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We used the whole-cell patch-clamp technique and monitoring of Fura-2 fluorescence to investigate the voltage dependence of the L-type Ca current (ICa,L) and intracellular Ca (Cai) transient in rabbit atrial myocytes at 37 degrees C. Imaging the atrial cell membrane with Di-4-ANNEPS showed (in contrast to ventricular cells) that atrial cells had very few transverse tubules. We measured ICa,L using a Cs-based internal dialysis solution to eliminate interfering K currents. The voltage dependence of peak ICa,L amplitude was bell-shaped: ICa,L was maximal at +10 mV and declined at more negative and positive potentials. For measuring the Fura-2 (Cai) transient, we used a K-based internal dialysis solution to preserve normal excitation-contraction coupling. Ryanodine (20 microM) plus thapsigargin (2 microM) (blockers of the sarcoplasmic reticulum, SR) abolished the phasic component of the Fura-2 transient (n = 5), demonstrating that the phasic Fura-2 transient provided an index of the magnitude of SR release. The Fura-2 transient also showed bell-shaped voltage dependence, but this was different from that for ICa,L. The Fura-2 transient peaked at +30 mV and partially declined at more positive potentials; but at potentials where inward ICa,L was small (if not absent), the phasic Fura-2 transient still attained a significant amplitude. We used a rapid application of nifedipine (32 microM), and of nifedipine plus 5 mM Ni, to assess the ability of ICa,L and reverse-mode Na-Ca exchange to trigger SR Ca release. With test pulses to +10 mV and +60 mV, a rapid switch to nifedipine (which blocked ICa,L) produced no significant reduction in phasic Fura-2 transient amplitude. This suggests that in the absence of ICa,L, another mechanism was able to trigger SR release. With pulses to +10 and +60 mV, a single beat switch to nifedipine plus 5 mM Ni almost completely abolished the phasic transient. Since 5 mM Ni inhibits Na-Ca exchange, this suggests that, in the absence of ICa,L, trigger Ca entry via reverse Na-Ca exchange was able to activate SR Ca release in atrial cells at 37 degrees C. The mechanisms underlying the Fura-2 transient in atrial cells, and differences with pre-existing data from rabbit ventricular cells, are discussed.

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Section: Fluorescence Measurementmentioning

confidence: 99%

Voltage dependence of the Fura-2 transient in rabbit left atrial myocytes at 37°C

Mitcheson

Hancox

Levi

1997

Pfl�gers Archiv European Journal of Physiology

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“…Preparation of cardiac myocytes from guinea pig and rat Cardiac myocytes were isolated from rat and guinea-pig hearts by a combination of enzymic and mechanical dispersion as described previously (Lee and Levi, 1991), but with the modifications described below. For both rat and guinea-pig, the perfusion flow rate was kept constant at 9 ml/min per g of heart tissue.…”

Section: Experimental Materialsmentioning

confidence: 99%

Characterization of the inhibition by stilbene disulphonates and phloretin of lactate and pyruvate transport into rat and guinea-pig cardiac myocytes suggests the presence of two kinetically distinct carriers in heart cells

Wang

Poole

Halestrap

et al. 1993

Biochemical Journal

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1. The kinetics of transport of pyruvate (Km 0.20 mM), L-lactate (Km 2.2 mM) and D-lactate (Ki 10.2 mM) into rat cardiac myocytes were studied and compared with those for guinea-pig heart cells [Poole, Halestrap, Price and Levi (1989) Biochem. J. 264, 409-418] whose equivalent values were 0.07, 2.3 and 6.6 mM respectively. Maximal rates of transport were about 5-fold higher in the rat heart cells. 2. 4,4'-Dibenzamidostilbene-2,2'-disulphonate (DBDS), a powerful inhibitor of monocarboxylate transport into erythrocytes [Poole & Halestrap (1991) Biochem. J. 275, 307-312], was found to be a potent but apparently partial inhibitor of lactate and pyruvate transport, with an apparent Ki value at 0.5 mM L-lactate of about 16 microM in both species. Maximal inhibition was 50% and 80% in rat and guinea-pig cells respectively. 3. The maximal extent of inhibition and apparent Ki values were dependent on both the substrate transported and its concentration. Maximum inhibition was less and the Ki was greater at higher substrate concentrations. 4. A variety of other stilbene disulphonates were studied which showed different Ki values and maximal extents of inhibition. 5. Phloretin was a significantly less potent inhibitor of transport into both rat (Ki 25 microM) and guinea-pig (Ki 16 microM) heart cells than into rat erythrocytes (Ki 1.4 microM). In the rat but not the guinea-pig heart cells, inhibition appeared partial (maximal inhibition 84%). 6. We demonstrate that our results can be explained by the presence of two monocarboxylate carriers in heart cells, both with Km values for L-lactate of about 2 mM and inhibited by alpha-cyano-4-hydroxycinnamate, but with different affinities for other substrates and inhibitors. One carrier is sensitive to inhibition by stilbene disulphonates and has lower Km values for pyruvate (0.05-0.10 mM) and D-lactate (5 mM), whereas the other has higher Km values for pyruvate (0.30 mM) and D-lactate (25 mM), and is relatively insensitive to stilbene disulphonates. Rat heart cells possess more of the latter carrier and guinea-pig heart cells more of the former. 7. The significance of these results for the study of lactate transport in the perfused heart is discussed.

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“…The apparatus used for fluorescence measurement has been described previously by Lee and Levi [23]. Only one change was made: the filter wheel (Cairn Research) carrying the 340 and 380 nm filters was rotated at 165 Hz to improve the time resolution of the Fura-2 signal (this gave one Fura-2 ratio measurement every 6 ms).…”

Section: Electrical Recordingmentioning

confidence: 99%

The Fura-2 transient can show two types of voltage dependence at 36°C in ventricular myocytes isolated from the rat heart

Hancox

Evans

Levi

1996

Pflugers Arch - Eur J Physiol

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We used the whole-cell patch-clamp method to investigate the voltage dependence of the L-type Ca current (ICa,L) and intracellular Ca (Cai) transient in ventricular myocytes isolated from the rat heart. Intracellular Ca was monitored using Fura-2 and the experiments were carried out at 36 degrees C. We measured ICa,L by using a caesium-based internal dialysis solution to eliminate interfering K currents. The voltage dependence of peak ICa,L amplitude was bell-shaped: ICa,L was maximal at +10 mV and declined at more positive potentials. When ICa,L was integrated over the first 25 ms to estimate the magnitude of Ca entry, this had a very similar voltage dependence to peak ICa,L. In all cells, phasic Fura-2 transients were abolished by 5 microM ryanodine (a blocker of the sarcoplasmic reticulum, SR) showing that the Fura-2 transient provided an index of the magnitude of SR Ca release. For experiments measuring the Cai transient, we used a K-based internal dialysis solution to preserve normal excitation-contraction coupling. In 30-40% of cells, we found that the Fura-2 transient had a bell-shaped voltage dependence. This suggests that, in these cells, the primary trigger mechanism for Ca-induced Ca-release might have been Ca entry via ICa,L. In the remaining 60-70% of cells, the voltage dependence of the Fura-2 transient was not bell-shaped. The Fura-2 transient reached a maximum with a pulse to +10 mV, and the amplitude of the transient did not decline significantly at more positive potentials to this. In cells with a non-bell-shaped voltage dependence of the Fura-2 transient, pulses to potentials as far positive as +140 mV elicited phasic Fura-2 transients. Since this potential exceeded the Nernst potential for Ca, it was unlikely there was any trigger Ca entry via ICa,L at this potential. This would suggest that, in these cells, another trigger for SR Ca release (in addition to ICa,L) might be present. We conclude that rat ventricular myocytes, produced using a standard isolation technique and under standard recording conditions, can show either a bell-shaped or a sigmoidal voltage dependence of the Fura-2 transient.

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The Role of Intracellular Sodium in the Control of Cardiac Contraction^a

Cited by 26 publications

References 22 publications

Voltage dependence of the Fura-2 transient in rabbit left atrial myocytes at 37°C

Voltage dependence of the Fura-2 transient in rabbit left atrial myocytes at 37°C

Characterization of the inhibition by stilbene disulphonates and phloretin of lactate and pyruvate transport into rat and guinea-pig cardiac myocytes suggests the presence of two kinetically distinct carriers in heart cells

The Fura-2 transient can show two types of voltage dependence at 36°C in ventricular myocytes isolated from the rat heart

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The Role of Intracellular Sodium in the Control of Cardiac Contractiona

Cited by 26 publications

References 22 publications

Voltage dependence of the Fura-2 transient in rabbit left atrial myocytes at 37°C

Voltage dependence of the Fura-2 transient in rabbit left atrial myocytes at 37°C

Characterization of the inhibition by stilbene disulphonates and phloretin of lactate and pyruvate transport into rat and guinea-pig cardiac myocytes suggests the presence of two kinetically distinct carriers in heart cells

The Fura-2 transient can show two types of voltage dependence at 36°C in ventricular myocytes isolated from the rat heart

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The Role of Intracellular Sodium in the Control of Cardiac Contraction^a