Effects of action potential duration on excitation-contraction coupling in rat ventricular myocytes. Action potential voltage-clamp measurements.

Although each of the fundamental processes involved in excitation-contraction coupling in mammalian heart has been identified, many quantitative details remain unclear. The initial goal of our experiments was to measure both the transmembrane Ca2+ current, which triggers contraction, and the Ca2+ extrusion due to Na(+)-Ca2+ exchange in a single ventricular myocyte. An action potential waveform was used as the command for the voltage-clamp circuit, and the membrane potential, membrane current, [Ca2+]i, and contraction (unloaded cell shortening) were monitored simultaneously. Ca(2+)-dependent membrane current during an action potential consists of two components: (1) Ca2+ influx through L-type Ca2+ channels (ICa-L) during the plateau of the action potential and (2) a slow inward tail current that develops during repolarization negative to approximately -25 mV and continues during diastole. This slow inward tail current can be abolished completely by replacement of extracellular Na+ with Li+, suggesting that it is due to electrogenic Na(+)-Ca2+ exchange. In agreement with this, the net charge movement corresponding to the inward component of the Ca(2+)-dependent current (ICa-L) was approximately twice that during the slow inward tail current, a finding that is predicted by a scheme in which the Ca2+ that enters during ICa is extruded during diastole by a 3 Na(+)-1 Ca2+ electrogenic exchanger. Action potential duration is known to be a significant inotropic variable, but the quantitative relation between changes in Ca2+ current, action potential duration, and developed tension has not been described in a single myocyte. We used the action potential voltage-clamp technique on ventricular myocytes loaded with indo 1 or rhod 2, both Ca2+ indicators, to study the relation between action potential duration, ICa-L, and cell shortening (inotropic effect). A rapid change from a "short" to a "long" action potential command waveform resulted in an immediate decrease in peak ICa-L and a marked slowing of its decline (inactivation). Prolongation of the action potential also resulted in slowly developing increases in the magnitude of Ca2+ transients (145 +/- 2%) and unloaded cell shortening (4.0 +/- 0.4 to 7.6 +/- 0.4 microns). The time-dependent nature of these effects suggests that a change in Ca2+ content (loading) of the sarcoplasmic reticulum is responsible. Measurement of [Ca2+]i by use of rhod 2 showed that changes in the rate of rise of the [Ca2+]i transient (which in rat ventricle is due to the rate of Ca2+ release from the sarcoplasmic reticulum) were closely correlated with changes in the magnitude and the time course of ICa-L.(ABSTRACT TRUNCATED AT 400 WORDS)

[1]  L. Blatter,et al.  Intracellular diffusion, binding, and compartmentalization of the fluorescent calcium indicators indo-1 and fura-2. , 1990, Biophysical journal.

[2]  E. Haber,et al.  The heart and cardiovascular system , 1986 .

[3]  D. T. Yue,et al.  Submicroscopic Ca2+ diffusion mediates inhibitory coupling between individual Ca2+ channels , 1992, Neuron.

[4]  D. Eisner,et al.  The effects of inhibitors of sarcoplasmic reticulum function on the systolic Ca2+ transient in rat ventricular myocytes. , 1993, The Journal of physiology.

[5]  M. Morad,et al.  Role of Ca2+ channel in cardiac excitation‐contraction coupling in the rat: evidence from Ca2+ transients and contraction. , 1991, The Journal of physiology.

[6]  D. Fedida,et al.  Mechanisms for the positive inotropic effect of alpha 1-adrenoceptor stimulation in rat cardiac myocytes. , 1992, Circulation research.

[7]  R. Tsien,et al.  A new generation of Ca2+ indicators with greatly improved fluorescence properties. , 1985, The Journal of biological chemistry.

[8]  J. Berlin,et al.  Ca2+ transients in cardiac myocytes measured with high and low affinity Ca2+ indicators. , 1993, Biophysical journal.

[9]  A. Zygmunt,et al.  Properties of the calcium-activated chloride current in heart , 1992, The Journal of general physiology.

[10]  M. F. Schneider,et al.  Inactivation of calcium release from the sarcoplasmic reticulum in frog skeletal muscle. , 1988, The Journal of physiology.

[11]  D. Allen On the relationship between action potential duration and tension in cat papillary muscle. , 1977, Cardiovascular research.

[12]  W. Lederer,et al.  Cellular and subcellular heterogeneity of [Ca2+]i in single heart cells revealed by fura-2. , 1987, Science.

[13]  W. Giles,et al.  Alpha‐adrenergic modulation of the transient outward current in rabbit atrial myocytes. , 1990, The Journal of physiology.

[14]  C W Balke,et al.  Processes that remove calcium from the cytoplasm during excitation‐contraction coupling in intact rat heart cells. , 1994, The Journal of physiology.

[15]  E. Lakatta,et al.  Excitation‐contraction coupling in the heart: the state of the question 1 , 1992, FASEB journal : official publication of the Federation of American Societies for Experimental Biology.

[16]  W. Giles,et al.  Heterogeneity of action potential waveforms and potassium currents in rat ventricle. , 1993, Cardiovascular research.

[17]  C W Balke,et al.  Local control of excitation‐contraction coupling in rat heart cells. , 1994, The Journal of physiology.

[18]  Akinori Noma,et al.  Na-Ca exchange current in mammalian heart cells , 1986, Nature.

[19]  J. Sutko Ryanodine Alteration of the Contractile State of Rat Ventricular Myocardium: Comparison with Dog, Cat, and Rabbit Ventricular Tissues , 1980, Circulation research.

[20]  W. Trautwein,et al.  Does the Calcium Current Modulate the Contraction of the Accompanying Beat?: A Study of E‐C Coupling in Mammalian Ventricular Muscle using Cobalt Ions , 1981, Circulation research.

[21]  E. Lakatta,et al.  Beta 1-adrenoceptor stimulation and beta 2-adrenoceptor stimulation differ in their effects on contraction, cytosolic Ca2+, and Ca2+ current in single rat ventricular cells. , 1993, Circulation research.

[22]  A. Zygmunt,et al.  Calcium-activated chloride current in rabbit ventricular myocytes. , 1991, Circulation research.

[23]  G. Brierley,et al.  Calcium accumulation and release by the sarcoplasmic reticulum of digitonin-lysed adult mammalian ventricular cardiomyocytes. , 1990, The Journal of biological chemistry.

[24]  S. Györke,et al.  Role of local Ca2+ domains in activation of Ca(2+)-induced Ca2+ release in crayfish muscle fibers. , 1993, The American journal of physiology.

[25]  A. Fabiato,et al.  Myoplasmic free calcium concentration reached during the twitch of an intact isolated cardiac cell and during calcium-induced release of calcium from the sarcoplasmic reticulum of a skinned cardiac cell from the adult rat or rabbit ventricle , 1981, The Journal of general physiology.

[26]  M. Morad,et al.  Excitation-contraction coupling in heart muscle: Membrane control of development of tension , 1973 .

[27]  V. Schouten The negative correlation between action potential duration and force of contraction during restitution in rat myocardium. , 1986, Journal of molecular and cellular cardiology.

[28]  S. Györke,et al.  Calcium‐induced calcium release in crayfish skeletal muscle. , 1992, The Journal of physiology.

[29]  R. Tsien,et al.  Fluorescent indicators for cytosolic calcium based on rhodamine and fluorescein chromophores. , 1989, The Journal of biological chemistry.

[30]  G. M. Briggs,et al.  Role of intracellular sodium in the regulation of intracellular calcium and contractility. Effects of DPI 201-106 on excitation-contraction coupling in human ventricular myocardium. , 1988, The Journal of clinical investigation.

[31]  G. Isenberg,et al.  Ca2+ load of guinea‐pig ventricular myocytes determines efficacy of brief Ca2+ currents as trigger for Ca2+ release. , 1994, The Journal of physiology.

[32]  K. Spitzer,et al.  A video system for measuring motion in contracting heart cells , 1988, IEEE Transactions on Biomedical Engineering.

[33]  A. J. Williams,et al.  Sheep cardiac sarcoplasmic reticulum calcium‐release channels: modification of conductance and gating by temperature. , 1991, The Journal of physiology.

[34]  W. Wier,et al.  Mechanism of release of calcium from sarcoplasmic reticulum of guinea‐pig cardiac cells. , 1988, The Journal of physiology.

[35]  G. Isenberg,et al.  Total and free myoplasmic calcium during a contraction cycle: x‐ray microanalysis in guinea‐pig ventricular myocytes. , 1991, The Journal of physiology.

[36]  B. Wohlfart Relationships between peak force, action potential duration and stimulus interval in rabbit myocardium. , 1979, Acta physiologica Scandinavica.

[37]  W. Lederer,et al.  Spatial non-uniformities in [Ca2+]i during excitation-contraction coupling in cardiac myocytes. , 1994, Biophysical journal.

[38]  D. Noble 6 – Sodium–Calcium Exchange and Its Role in Generating Electric Current , 1986 .

[39]  D. Bers,et al.  Intracellular Ca transients in rat cardiac myocytes: role of Na-Ca exchange in excitation-contraction coupling. , 1990, The American journal of physiology.

[40]  M. Pinter,et al.  Time courses of calcium and calcium-bound buffers following calcium influx in a model cell. , 1993, Biophysical journal.

[41]  A. Brown,et al.  A Comparison of Calcium Currents in Rat and Guinea Pig Single Ventricular Cells , 1984, Circulation research.

[42]  W. Giles,et al.  Role of sodium‐calcium exchange in activation of contraction in rat ventricle. , 1993, The Journal of physiology.

[43]  E. Neher,et al.  Calcium gradients and buffers in bovine chromaffin cells. , 1992, The Journal of physiology.

[44]  W. Lederer,et al.  Calcium sparks: elementary events underlying excitation-contraction coupling in heart muscle. , 1993, Science.

[45]  W. Wier,et al.  Flux of Ca2+ across the sarcoplasmic reticulum of guinea‐pig cardiac cells during excitation‐contraction coupling. , 1991, The Journal of physiology.

[46]  R. D. Nathan Cardiac muscle : the regulation of excitation and contraction , 1986 .

[47]  H. T. ter Keurs,et al.  Force-interval relations of twitches and cold contractures in rat cardiac trabeculae. Effect of ryanodine. , 1991, Circulation research.

[48]  W. Rose,et al.  Macroscopic and unitary properties of physiological ion flux through L‐type Ca2+ channels in guinea‐pig heart cells. , 1992, The Journal of physiology.

[49]  E. Lakatta,et al.  Single adult rabbit and rat cardiac myocytes retain the Ca2+- and species-dependent systolic and diastolic contractile properties of intact muscle , 1986, The Journal of general physiology.

[50]  D M Bers,et al.  Diffusion around a cardiac calcium channel and the role of surface bound calcium. , 1991, Biophysical journal.

[51]  P. Lipp,et al.  Modulation of Ca2+ release in cultured neonatal rat cardiac myocytes. Insight from subcellular release patterns revealed by confocal microscopy. , 1994, Circulation research.

[52]  W. Lederer,et al.  Na-Ca exchange: stoichiometry and electrogenicity. , 1985, The American journal of physiology.

[53]  P. Sulakhe,et al.  Excitation-contraction coupling in heart. VII. Calcium accumulation in subcellular particles in congestive heart failure. , 1971, The Journal of clinical investigation.

[54]  I. Imanaga,et al.  Calcium modulation of single SR potassium channel currents in heart muscle. , 1994, Journal of molecular and cellular cardiology.

[55]  W. Giles,et al.  Contributions of a transient outward current to repolarization in human atrium. , 1989, The American journal of physiology.

[56]  J. Arreola,et al.  Ca2+ current and Ca2+ transients under action potential clamp in guinea pig ventricular myocytes. , 1991, The American journal of physiology.

[57]  L. Stehno-Bittel,et al.  Spontaneous sarcoplasmic reticulum calcium release and extrusion from bovine, not porcine, coronary artery smooth muscle. , 1992, The Journal of physiology.

[58]  W. Giles,et al.  Regulation of unloaded cell shortening by sarcolemmal sodium‐calcium exchange in isolated rat ventricular myocytes. , 1993, The Journal of physiology.

[59]  M. Morad,et al.  Role of Ca2+ channel in development of tension in heart muscle. , 1987, Journal of molecular and cellular cardiology.

[60]  A. Fabiato,et al.  Time and calcium dependence of activation and inactivation of calcium- induced release of calcium from the sarcoplasmic reticulum of a skinned canine cardiac Purkinje cell , 1985, The Journal of general physiology.

[61]  Donald M. Bers,et al.  Excitation-Contraction Coupling and Cardiac Contractile Force , 1991, Developments in Cardiovascular Medicine.

[62]  D. Eisner,et al.  The relative contributions of different intracellular and sarcolemmal systems to relaxation in rat ventricular myocytes. , 1993, Cardiovascular research.

[63]  R A Bassani,et al.  Relaxation in rabbit and rat cardiac cells: species‐dependent differences in cellular mechanisms. , 1994, The Journal of physiology.

[64]  D. Bers,et al.  Intrinsic cytosolic calcium buffering properties of single rat cardiac myocytes. , 1994, Biophysical journal.

[65]  U. Ravens,et al.  Comparison of the action potential prolonging and positive inotropic activity of DPI 201-106 and BDF 9148 in human ventricular myocardium. , 1994, Journal of molecular and cellular cardiology.

[66]  A. Noma,et al.  Calcium‐activated non‐selective cation channel in ventricular cells isolated from adult guinea‐pig hearts. , 1988, The Journal of physiology.

[67]  J. R. Monck,et al.  Localization of the site of Ca2 + release at the level of a single sarcomere in skeletal muscle fibres , 1994, Nature.

[68]  D. Noble,et al.  Effects of rapid changes of external Na+ concentration at different moments during the action potential in guinea‐pig myocytes. , 1994, The Journal of physiology.

[69]  A. Fabiato Simulated calcium current can both cause calcium loading in and trigger calcium release from the sarcoplasmic reticulum of a skinned canine cardiac Purkinje cell , 1985, The Journal of general physiology.

[70]  E H Wood,et al.  Inotropic Effects of Electric Currents , 1969, Circulation research.

[71]  M. Morad,et al.  Regulation of calcium release is gated by calcium current, not gating charge, in cardiac myocytes. , 1989, Science.

[72]  W. Wier Cytoplasmic [Ca2+] in mammalian ventricle: dynamic control by cellular processes. , 1990, Annual review of physiology.

[73]  T. Mcdonald,et al.  Regulation and modulation of calcium channels in cardiac, skeletal, and smooth muscle cells. , 1994, Physiological reviews.

[74]  C. Luo,et al.  A dynamic model of the cardiac ventricular action potential. I. Simulations of ionic currents and concentration changes. , 1994, Circulation research.

[75]  U. Ravens,et al.  Transient outward current in human ventricular myocytes of subepicardial and subendocardial origin. , 1994, Circulation research.

[76]  M. Stern,et al.  Theory of excitation-contraction coupling in cardiac muscle. , 1992, Biophysical journal.

[77]  D M Bers,et al.  Passive Ca buffering and SR Ca uptake in permeabilized rabbit ventricular myocytes. , 1993, The American journal of physiology.

[78]  E Page,et al.  Quantitative ultrastructural analysis in cardiac membrane physiology. , 1978, The American journal of physiology.

[79]  B. R. Jewell,et al.  Analysis of the effects of changes in rate and rhythm upon electrical activity in the heart. , 1980, Progress in biophysics and molecular biology.

[80]  W. Barry,et al.  Intracellular Calcium Homeostasis in Cardiac Myocytes , 1993, Circulation.

[81]  J. Hancox,et al.  A role for depolarisation induced calcium entry on the Na-Ca exchange in triggering intracellular calcium release and contraction in rat ventricular myocytes. , 1993, Cardiovascular research.

[82]  B. London,et al.  Contraction in voltage-clamped, internally perfused single heart cells , 1986, The Journal of general physiology.

[83]  B. Hille,et al.  Calcium homeostasis in identified rat gonadotrophs. , 1994, The Journal of physiology.

[84]  D. Noble,et al.  The Role of Sodium ‐ Calcium Exchange during the Cardiac Action Potential a , 1991, Annals of the New York Academy of Sciences.

[85]  J. Meldolesi,et al.  Molecular and cellular physiology of intracellular calcium stores. , 1994, Physiological reviews.

[86]  R. Zucker,et al.  Aequorin response facilitation and intracellular calcium accumulation in molluscan neurones , 1980, The Journal of physiology.

[87]  E. Lakatta,et al.  Buffering of calcium influx by sarcoplasmic reticulum during the action potential in guinea‐pig ventricular myocytes. , 1993, The Journal of physiology.

[88]  J. Jalife,et al.  Cardiac Electrophysiology: From Cell to Bedside , 1990 .

[89]  S. Györke,et al.  Ca(2+)‐dependent negative control mechanism for Ca(2+)‐induced Ca2+ release in crayfish muscle. , 1994, The Journal of physiology.