PubMed Health⌕ Search

Biomedical subjects

D T Yue

Publications and source records attributed to D T Yue.

At least 19 recordsLinked to original sources
PubMed1992

Molecular localization of an ion-binding site within the pore of mammalian sodium channels.

Sodium channels are the major proteins that underlie excitability in nerve, heart, and skeletal muscle. Chemical reaction rate theory was used to analyze the blockage of single wild-type and mutant sodium channels by cadmium ions. The affinity of cadmium for the native tetrodotoxin (TTX)-resistant cardiac channel was much higher than its affinity for the TTX-sensitive skeletal muscle isoform of the channel (microliters). Mutation of Tyr401 to Cys, the corresponding residue in the cardiac sequence, rendered microliters highly susceptible to cadmium blockage but resistant to TTX. The binding site was localized approximately 20% of the distance down the electrical field, thus defining the position of a critical residue within the sodium channel pore.

Amino Acid Sequence↗
PubMed1992

Submicroscopic Ca2+ diffusion mediates inhibitory coupling between individual Ca2+ channels.

Dihydropyridine-sensitive Ca2+ channels in heart demonstrate an important negative feedback property: they close, or inactivate, in response to prior Ca2+ entry. We now find that Ca2+ influx through one channel can selectively contribute to the inactivation of another adjacent channel, without a generalized elevation of bulk intracellular Ca2+ concentration. Intracellular application of the Ca2+ chelator BAPTA greatly diminishes such negative interactions within Ca2+ channel pairs. These findings demonstrate that Ca2+ currents are controlled not only by intrinsic channel properties, but also by local diffusive interactions among neighboring channels. Such inhibitory coupling among channels provides a concrete example of localized Ca2+ signaling, long proposed to exist on the basis of theoretical calculations.

Animals↗
PubMed1991

Sodium channel inactivation from resting states in guinea-pig ventricular myocytes.

1. Unitary Na+ channel currents were recorded from isolated guinea-pig ventricular myocytes using the cell-attached patch-clamp technique with high [Na+] in the pipette to enhance the signal-to-noise ratio. 2. The probability that the channel enters the inactivated state (I) directly from resting states (C) was investigated over a wide range of membrane potentials. 3. At membrane potentials of -60 mV or more positive, Markov chain theory was used to estimate the probability of C----I from histograms of the number of channel openings per depolarizing period. Holding potentials at least as negative as -136 were required to ensure that all channels resided in C prior to depolarization. 4. At membrane potentials negative to -60 mV, a two-pulse protocol was employed to determine the probability of C----I from the fraction of blank sweeps during the pre-pulse with correction for missed events. 5. The probability of C----I was found to be steeply voltage dependent at negative potentials, falling from 0.87 +/- 0.03 (mean +/- S.D.) at -91 mV to 0.42 +/- 0.01 at -76 mV. At potentials positive to -60 mV, this probability was less steeply voltage dependent and decayed to near zero at 0 mV. 6. Under physiological conditions, C----I transitions may produce appreciable Na+ channel inactivation at diastolic potentials. At potentials above the action potential threshold, inactivation is much more likely to occur from the open state.

Action Potentials↗
PubMed1991

Delayed end ejection increases isovolumic ventricular relaxation rate in isolated perfused canine hearts.

We sought to determine the ejection variables that are principally responsible for increases in isovolumic ventricular relaxation rate observed with increases in stroke volume. In nine isolated canine hearts, left ventricular ejection was controlled by patterns specially designed to isolate the ejection parameters most critical to isovolumic relaxation rate. When stroke volume was augmented by increases in end-diastolic volume (EDV) with end-systolic volume (ESV) held constant, isovolumic ventricular relaxation rate was unchanged, as gauged by the time constants of single-exponential fits to decaying pressure. In contrast, when ESV was decreased with EDV held constant, isovolumic relaxation time constants decreased significantly, from approximately 100 to 70 msec (protocol I). The important difference in these two situations might have been that the time of end ejection was delayed in the case with faster isovolumic relaxation. To rule out other parameters that may have influenced isovolumic relaxation, ejection velocity was varied in another protocol (protocol II) by either delays in time of the onset of ejection or advances in end-ejection time, always with constant ESV and EDV. Here isovolumic relaxation was progressively slowed as end ejection occurred earlier, whereas isovolumic relaxation rate was insensitive to changes in the onset of ejection, consistent with the unique importance of end ejection to isovolumic relaxation. In fact, our analysis reveals the remarkable finding that changes in isovolumic relaxation time constant produced by either protocol I or protocol II could be related quantitatively to end ejection by a single curve.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Calcium-sensitive inactivation in the gating of single calcium channels.

Voltage-activated calcium channels open and close, or gate, according to molecular transition rates that are regulated by transmembrane voltage and neurotransmitters. Here evidence for the control of gating by calcium was found in electrophysiological records of single, L-type calcium channels in heart cells. Conditional open probability analysis revealed that calcium entry during the opening of a single channel produces alterations in gating transition rates that evolve over the course of hundreds of milliseconds. Such alteration of calcium-channel gating by entry of a favored permeant ion provides a mechanism for the short-term modulation of single-ion channels.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1990

Beta-adrenergic stimulation of calcium channels occurs by potentiation of high-activity gating modes.

cAMP-dependent phosphorylation clearly increases current through cardiac L-type Ca channels, but the molecular manifestation of this effect remains controversial. Previous work implicates either an increase in the number of functional channels or graded changes in the gating of individual channels. We now find that single cardiac Ca channels display three patterns of activity ("modes") and that isoproterenol or 8-bromoadenosine 3',5'-cyclic monophosphate redistributes the relative proportions of modes such that the two most active (mode 1, bursts of brief openings; mode 2, very long-lasting openings) are favored (P less than 0.05; n = 7). Conversely, a pattern of sparse brief openings (mode 0a) is selectively inhibited (P less than 0.01). Despite differences in the relative frequencies of the various modes before and during drug exposure, the gating within each mode is not detectably changed. We conclude that potentiation of highly active modes of Ca channel gating underlies the enhancement of calcium influx by beta-adrenergic stimulation.

1-Methyl-3-isobutylxanthine↗
PubMed1990

Permeation in the dihydropyridine-sensitive calcium channel. Multi-ion occupancy but no anomalous mole-fraction effect between Ba2+ and Ca2+.

We investigated the mechanism whereby ions cross dihydropyridine-sensitive (L-type) Ca channels in guinea pig ventricular myocytes. At the single-channel level, we found no evidence of an anomalous mole-fraction effect like that reported previously for whole-cell currents in mixtures of Ba and Ca. With the total concentration of Ba + Ca kept constant at 10 (or 110) mM, neither conductance nor absolute unitary current exhibits a paradoxical decrease when Ba and Ca are mixed, thereby weakening the evidence for a multi-ion permeation scheme. We therefore sought independent evidence to support or reject the multi-ion nature of the L-type Ca channel by measuring conductance at various permeant ion concentrations. Contrary to the predictions of models with only one binding site in the permeation pathway, single-channel conductance does not follow Michaelis-Menten kinetics as Ba activity is increased over three orders of magnitude. Two-fold variation in the Debye length of permeant ion solutions has little effect on conductance, making it unlikely that local surface charge effects could account for these results. Instead, the marked deviation from Michaelis-Menten behavior was best explained by supposing that the permeation pathway contains three or more binding sites that can be occupied simultaneously. The presence of three sites helps explain both a continued rise in conductance as [Ba2+] is increased above 110 mM, and the high single-channel conductance (approximately 7 pS) with 1 mM [Ba2+] as the charge carrier; the latter feature enables the L-type channel to carry surprisingly large currents at physiological divalent cation concentrations. Thus, despite the absence of an anomalous mole-fraction effect between Ba and Ca, we suggest that the L-type Ca channel in heart cells supports ion flux by a single-file, multi-ion permeation mechanism.

Animals↗
PubMed1990

Quantification of [Ca2+]i in perfused hearts. Critical evaluation of the 5F-BAPTA and nuclear magnetic resonance method as applied to the study of ischemia and reperfusion.

Calcium has been implicated as a mediator of cell injury in ischemia and reperfusion, but direct measurements of Ca2+ are required to refine this idea. We used nuclear magnetic resonance spectroscopy and the Ca2+ indicator 5F-BAPTA to measure [Ca2+]i in perfused ferret hearts. Several lines of evidence are presented to show that loading with the acetoxymethyl ester of 5F-BAPTA is not significantly complicated by accumulation of partially de-esterified metabolites, compartmentalization into mitochondria, or disproportionate uptake into endothelial cells. During 20 minutes of total global ischemia at 30 degrees C, time-averaged [Ca2+]i increased significantly, reaching peak values roughly three times control at 15-20 minutes. Reperfusion resulted in a persistent elevation of [Ca2+]i during the first 5 minutes, but not afterward. Although the nonlinear response of 5F-BAPTA to [Ca2+] leads to underestimation of the true time-averaged [Ca2+]i, the measured alterations of intracellular Ca2+ homeostasis during ischemia are large compared with the likely errors in quantification. Phosphorus nuclear magnetic resonance spectroscopy of 5F-BAPTA-loaded hearts reveals changes during ischemia similar to those recorded previously in hearts not containing a Ca2+ indicator. Developed pressure recovers to only 50% of control values during reflow, indicating that the presence of 5F-BAPTA in the cytosol does not protect against stunning, at least when the extracellular calcium concentration has been raised to 8 mM. We conclude that 5F-BAPTA provides useful measurements that reveal that time-averaged [Ca2+]i rises during ischemia and returns to control levels soon after reperfusion.

Animals↗
PubMed1989

Two molecular transitions influence cardiac sodium channel gating.

Sodium channels from diverse excitable membranes are very similar in their structure, yet surprisingly heterogeneous in their behavior. The processes that govern the opening and closing of sodium channels have appeared difficult to describe in terms of a single, unifying molecular scheme. Now cardiac sodium channels have been analyzed by high-resolution single-channel recordings over a broad range of potentials. Channels exhibited both complex and simple gating patterns at different voltages. Such behavioral diversity can be explained by the balance between two molecular transitions whereby channels can exit the open state.

Electric Conductivity↗
PubMed1989

Mechanically induced action potential changes and arrhythmia in isolated and in situ canine hearts.

Stretch of excised myocardial tissue causes electrophysiological and potentially arrhythmogenic changes in transmembrane action potentials but corresponding data of the intact mammalian heart are lacking. The effects of increases in ventricular volume and pressure on epicardial monophasic action potentials were therefore investigated in isolated, cross circulated and in situ canine hearts. In seven isolated hearts, increases in ventricular volume and pressure resulted in (1) a linearly related decrease in action potential amplitude (r = 0.988; slope = 0.41% amplitude.ml-1; volume intercept = 17.6 ml), mainly due to a decrease in maximum diastolic potential; (2) a decrease in action potential plateau duration (at 20% repolarisation) by 19 (SD 8)%; and (3) appearance of early afterdepolarizations, reaching up to 18% of total action potential amplitude. Afterdepolarizations occurred only when ventricular outflow was obstructed at end diastole but not at end systole. In eight in situ hearts, increase in left intraventricular pressure produced by transient occlusions of the ascending aorta was also accompanied by decrease in maximum diastolic potential and action potential plateau duration, and by appearance of early afterdepolarizations. In both isolated and in situ intact ventricles, the loading induced electrophysiological changes were associated with occurrence of ectopic ventricular beats. These data show that mechanical overload produces significant electrophysiological changes in the intact canine ventricle which may lead to arrhythmia.

Action Potentials↗
PubMed1988

A novel cardiac potassium channel that is active and conductive at depolarized potentials.

We report the existence of a novel potassium channel revealed in single-channel recordings from guinea-pig ventricular heart cells. The channel, observed in approximately 10% of patches, demonstrates a 14 pS conductance at physiological potassium concentrations, does not rectify over the voltage range of the action potential, and is quite selective for K ions. The channel activates with depolarization, but does not require intracellular Ca2+ ions to open. Open channel probability increases rapidly (less than 10 ms) to a plateau in response to depolarizing voltage steps, and demonstrates no detectable inactivation (greater than 600 ms). These features clearly distinguish this channel from other known K channels in cardiac muscle. Because of its high activity at plateau potentials, we propose the name iKp.

Animals↗
PubMed1988

In vitro studies of isolated supported human hearts.

We developed methods to revive human hearts, obtained at the time of cardiac transplantation, and study them in the physiology laboratory. The hearts were arrested with cardioplegic solution at the time of explanation and transported to the laboratory at 4 degrees C. The hearts were perfused with a human blood based solution whose flow rate, temperature, and ionic concentration were controlled. Six hearts with various endstage cardiomyopathies were revived in this manner. Once perfusion was started, the hearts maintained a steady contractile state for approximately 30 min during which time data could be collected. Within this time period we could measure end-systolic and end-diastolic pressure-volume relations, the time courses of contraction and relaxation, and the influence of heart rate and premature stimulation on contractile state. The results suggest that evidence of specific cellular abnormalities in human heart disease might be obtained from measurements of global ventricular performance. Furthermore, the type of abnormality identified, namely sarcoplasmic reticulum dysfunction, in several forms of cardiomyopathy was in concordance with results obtained in muscle bath studies of similarly diseased human and animal myocardium.

Cardiomyopathy, Dilated↗
PubMed1988

Effect of isoproterenol on force transient time course and on stiffness spectra in rabbit papillary muscle in barium contracture.

To determine whether catecholamines produce alterations in myocardial myosin-actin cycling kinetics, we investigated the effects of isoproterenol upon mechanical characteristics of constantly activated heart muscle thought to reflect crossbridge behavior. In isolated rabbit right ventricular papillary muscles in barium contracture at 24 degrees C, we found that 10 microM isoproterenol caused: (a) a 23% reduction of the 10 to 90% rise time of slow tension recovery in force transients induced by rapid, small amplitude stretches; and (b) a 23% increase in the frequency of sinusoidal length perturbation at which stiffness amplitude exhibited a minimum. Based upon previous mechanistic interpretations of force transients, and on an analysis developed here to relate crossbridge events to the frequency-dependence of stiffness, we argue that our observations provide evidence that isoproterenol induces an acceleration of crossbridge cycling rate. This raises the intriguing prospect that beta-adrenergic stimulation regulates contraction, not only by well-known alterations in calcium metabolism, but also by intrinsic modulation of the force-generating machinery itself.

Animals↗
PubMed1987

Influence of ventricular contractility on non-work-related myocardial oxygen consumption.

The relationship between myocardial oxygen consumption (MVO2) and the total pressure-volume area (PVA), which represents the total mechanical work performed during a cardiac cycle, has been shown to be linear and independent of loading conditions: MVO2 = aPVA + b. When inotropic state is enhanced, the MVO2-PVA relation shifts upward (increase in b), and when inotropic state is depressed the relation shifts downward (decrease in b). However, the quantitative relationship between contractility and b (the non-work-related myocardial oxygen consumption) determined over a wide range of contractilities is not known. In seven isolated blood perfused canine hearts, left ventricular (LV) contractility was increased by dobutamine and decreased with nifedipine or reduction of coronary blood flow. At each level of contractility, the end-systolic pressure-volume relationship (ESPVR) and the MVO2-PVA relation were determined. For each heart, the resulting values of b (ml O2/beat) were plotted as a function of Emax (mmHg/ml), an index of contractility defined as the slope of the ESPVR. There was a linear relation between Emax and b over a wide range of contractilities; on average, b (ml O2/beat) = 0.0036 Emax (mmHg/ml) + 0.0101 [r = 0.929-0.978 (95% confidence interval)], when Emax was varied over an average range of 2.8-9.6 mmHg/ml. These results suggest a common underlying determinant of contractility and non-work-related oxygen consumption.

Animals↗
PubMed1987

Intracellular free calcium concentration measured with 19F NMR spectroscopy in intact ferret hearts.

Changes in the intracellular free Ca2+ concentration, [Ca2+]i, mediate excitation-contraction coupling in the heart and contribute to cellular injury during ischemia and reperfusion. To study these processes directly, we measured [Ca2+]i in perfused ferret (Mustela putorius furo) hearts using 19F NMR spectroscopy to detect the 5,5'-difluoro derivative of the Ca2+ chelator 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA). To load cells, hearts were perfused with the acetoxymethyl ester derivative of 5,5'-F2-BAPTA. We measured 19F NMR spectra and left ventricular pressure simultaneously, at rest and during pacing at various external Ca concentrations [( Ca]o). Although contractile force was attenuated by the Ca2+ buffering properties of 5,5'-F2-BAPTA, the decrease in pressure could be overcome by raising [Ca]o. Our mean value of 104 nM for [Ca2+]i at rest in the perfused heart agrees well with previous measurements in isolated ventricular muscle. During pacing at 0.6-4 Hz, time-averaged [Ca2+]i increased; the effect of pacing was augmented by increasing [Ca]o. [Ca2+]i more than tripled during 10-20 min of global ischemia, and returned toward control levels upon reperfusion. This approach promises to be particularly useful in investigating the physiology of intact hearts and the pathophysiology of alterations in the coronary circulation.

Animals↗
PubMed1987

Intracellular [Ca2+] related to rate of force development in twitch contraction of heart.

The relation between the rate of rise of tension (dF/dt) and intracellular free Ca2+ concentration ([Ca2+]i) during twitch contraction was investigated in mammalian ventricular myocardium. [Ca2+]i was assessed from luminescence emitted by ferret papillary muscles microinjected with the calcium-regulated photoprotein aequorin. Evidence was found that during the phase of rising tension following maximum positive dF/dt, there was an approximately linear relationship between dF/dt at a given instant and the estimated [Ca2+]i at that same instant. A single such instantaneous relationship held true for physiological contractions of widely varying strength (n = 5 preparations), up to 65.3 +/- 6.0% (means +/- SE) of maximal Ca2+-activated force, as assessed from maximally activated cardiac tetani. Furthermore, the identical relationship determined from physiological contractions also held true for virtually the entire rising phase of tension in contractions with [Ca2+]i transients slowed (approximately 4- to 5-fold) by exposure of muscles to 5 microM ryanodine (n = 5 preparations). That a unique relation applies to contractions of both vastly different strength and time course provides evidence that the correlation between instantaneous dF/dt and [Ca2+]i is not merely fortuitous but indicates a fundamental property of myocardium. Such a property provides considerable insight into many features of physiological contraction and may represent a central clue as to the mechanism of activation in mammalian cardiac muscle.

Aequorin↗
PubMed1987

Contractility-dependent curvilinearity of end-systolic pressure-volume relations.

The shape of the end-systolic tension-length relationship (ESTLR) changes when contractile state is changed, whereas the end-systolic pressure-volume relationship (ESPVR) remains linear despite changes in contractility. To investigate this disparity, the ESPVR was determined with contractility altered extensively by dobutamine, BAY K 8644, nifedipine, lowering coronary blood flow, and the introduction of extrasystolic and postextrasystolic stimulations. The ESPVRs were fitted by nonlinear regression analysis to the parabolic equation Pes = aVes2 + bVes + c, where Pes is end-systolic pressure, Ves is end-systolic volume, and a, b, and c are parameters. There was a negative, statistically significant correlation between a, which serves as a shape index of the ESPVR, and E'max, the slope of the ESPVR in a low volume range. When E'max was large a was negative, indicating increasing concavity of the ESPVR to the volume axis at high contractility. When E'max was small a was positive, indicating convexity of the ESPVRs to the volume axis at low contractility. Within the average range of E'max between 3.4 and 7.8 mmHg/ml, however, the parabolic fit to the data was not statistically better than a linear fit over the range of volumes testable in the isolated heart. We conclude that the shape of the ESPVR measured in the isolated canine heart changes with contractile state. In accordance with previous interpretations of shape changes in the muscle ESTLR, these results are consistent with the existence of length-dependent activation of cardiac muscle in the intact heart.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗