Effects of sarcoplasmic reticulum Ca2+ load on the gain function of Ca2+ release by Ca2+ current in cardiac cells

1995 ◽  
Vol 268 (2) ◽  
pp. H916-H920 ◽  
Author(s):  
A. M. Janczewski ◽  
H. A. Spurgeon ◽  
M. D. Stern ◽  
E. G. Lakatta
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Voltage Clamp ◽  
Ventricular Myocytes ◽  
Cell Voltage ◽  
Cardiac Cells ◽  
Gain Function ◽  
Whole Cell ◽  
Rat Ventricular Myocytes

We studied the effects of variable sarcoplasmic reticulum (SR) Ca2+ loading on changes in the gain index of Ca2+ release from the SR, measured as the ratio of the amount of Ca2+ released to the magnitude of the Ca2+ current (ICa) integrated for the initial 20 ms of the depolarization, in whole cell voltage-clamped rat ventricular myocytes dialyzed with the Ca2+ indicator indo 1 salt at 23 degrees C. Changes in ICa were measured directly, and changes in the SR Ca2+ release were indexed by changes in the amplitudes and rates of rise of cytosolic Ca2+ (Ca2+i) transients. The SR Ca2+ load was graded by the duration of conditioning voltage-clamp steps and verified by caffeine-dependent Ca2+i transients. A train of abbreviated (from 100 to 20 ms) voltage-clamp depolarizations, which triggers SR Ca2+ release but fails to replenish the SR with Ca2+, diminished the SR Ca2+ load by 56 +/- 5%, did not alter peak ICa but reduced the amplitudes of the ICa-dependent Ca2+i transients by 52 +/- 3%, and decreased the gain index by 60 +/- 3% (SE; n = 5 or 6). Changes in the amplitudes of Ca2+i transients elicited by ICa and changes in the gain index were linearly correlated (r2 = 0.83 and 0.79, respectively; P < 0.001 for each) with changes in amplitudes of Ca2+i transients elicited by caffeine pulses applied in lieu of the respective voltage-clamp pulses.(ABSTRACT TRUNCATED AT 250 WORDS)

Steady-state twitch Ca2+ fluxes and cytosolic Ca2+ buffering in rabbit ventricular myocytes

1996 ◽  
Vol 270 (1) ◽  
pp. C192-C199 ◽  
Author(s):  
L. M. Delbridge ◽  
J. W. Bassani ◽  
D. M. Bers
Keyword(s):  
Steady State ◽  
Sarcoplasmic Reticulum ◽  
Voltage Clamp ◽  
Ventricular Myocytes ◽  
Cell Voltage ◽  
Whole Cell ◽  
Rabbit Ventricular Myocytes ◽  
The Mean ◽  
State Contraction ◽  
Caffeine Contractures

Intracellular Ca2+ ([Ca2+]i) transients and transsarcolemmal Ca2+ currents were measured in indo 1-loaded isolated rabbit ventricular myocytes during whole cell voltage clamp to quantitate the components of cytosolic Ca2+ influx and to describe the dynamic aspects of cytosolic Ca2+ buffering during steady-state contraction (0.5 Hz, 22 degrees C). Sarcolemmal Ca2+ influx was directly measured from the integrated Ca2+ current (Ica) recorded during the clamp (158 +/- 10 attomoles; amol). Sarcoplasmic reticulum (SR) Ca2+ content was determined from the integrated electrogenic Na+/Ca2+ exchange current (Ix) induced during rapid application and sustained exposure of cells to caffeine to elicit the release of the SR Ca2+ load (1,208 +/- 170 amol). The mean steady-state SR Ca2+ load was calculated to be 87 +/- 13 microM (mumol/l nonmitochondrial cytosolic volume). Ca2+ influx via Ica represented approximately 14% of the stored SR Ca2+ and 23% of the total cytosolic Ca2+ flux during a twitch (47 +/- 6 microM). Comparison of electrophysiologically measured Ca2+ fluxes with Ca2+ transients yields apparent buffering values of 60 for caffeine contractures and 110 for twitches (delta Ca2+ total/delta Ca2+ free). This is consistent with the occurrence of "active" buffering of cytosolic Ca2+ by SR Ca2+ uptake during the twitch.

Effects of endothelin 1 on calcium and sodium currents in isolated human cardiac myocytes

1995 ◽  
Vol 73 (12) ◽  
pp. 1774-1783 ◽  
Author(s):  
Tzu-Hurng Cheng ◽  
Chung-Yi Chang ◽  
Jeng Wei ◽  
Cheng-I Lin
Keyword(s):  
Voltage Clamp ◽  
Cardiac Myocytes ◽  
Ventricular Myocytes ◽  
Cell Voltage ◽  
Cardiac Cells ◽  
Sodium Currents ◽  
Atrial Myocytes ◽  
Whole Cell ◽  
Voltage Clamp Technique ◽  
Endothelin 1

We have used the whole-cell voltage-clamp technique to study the effects of endothelin 1 (ET-1, 10 nM) on L-type Ca2+ currents and voltage-dependent Na+ inward currents in human cardiac cells. Myocytes were enzymatically isolated from atrial specimens obtained during open-heart surgery and from human ventricular tissues of explanted hearts. Extracellular application of ET-1 decreased the peak amplitude of Ca2+ currents by 26 ± 6% (n = 13) in atrial myocytes and by 19 ± 3% (n = 8) in ventricular myocytes. In three atrial cells, treatment with 1 μM BQ123 prevented the decrease in Ca2+ currents induced by ET-1. When GTP (0.2 mM) was added to the dialyzing pipette solution, ET-1 still caused a small decline by 12 ± 5% (n = 16), in peak Ca2+ currents, in atrial myocytes. When Ca2+ currents were increased (+210 ± 19%) by a β-adrenoceptor agonist (0.1 μM isoproterenol) or by the phosphodiesterase inhibitor isobutylmethylxanthine (10 μM), ET-1 reduced Ca2+ currents by 35 ± 6% (n = 4) and 30 ± 4% (n = 5), respectively. In human ventricular myocytes in the presence of 1 μM isoproterenol, which increased the peak Ca2+ currents by 150 ± 30%, ET-1 also induced a drastic reduction in Ca2+ currents, by 40 ± 11% (n = 5). The tetrodotoxin-sensitive Na+ currents measured in the presence of 5 mM [Na]o were significantly enhanced (+28 ± 7%) by ET-1 in five atrial myocytes. The stimulatory effect of ET-1 on Na+ currents was partially reversible. The present findings in human cardiac cells show that ET-1 did not enhance the Ca2+ currents in the absence or presence of internal GTP. The positive inotropic actions induced by ET-1 in human heart may be mediated mainly by signal-transduction pathways other than the G-protein – adenylyl cyclase – cAMP system.Key words: endothelin 1, human cardiac myocytes, whole-cell voltage-clamp technique, calcium currents, sodium currents.

α1-Adrenergic activation of L-type Ca current in rat ventricular myocytes: perforated patch-clamp recordings

1998 ◽  
Vol 274 (6) ◽  
pp. H2203-H2207 ◽  
Author(s):  
Shi J. Liu ◽  
Richard H. Kennedy
Keyword(s):  
Ventricular Myocytes ◽  
Cell Voltage ◽  
Adrenergic Stimulation ◽  
Whole Cell ◽  
Rat Ventricular Myocytes ◽  
Perforated Patch ◽  
Adult Rat ◽  
Transient Decrease ◽  
Adrenergic Antagonist ◽  
Patch Configuration

α1-Adrenergic stimulation has little effect on L-type Ca2+channel current ( I Ca,L) in adult cardiac myocytes measured using conventional whole cell voltage-clamp techniques. In this study using perforated-patch techniques, we reevaluated the effect of α1-adrenergic stimulation on I Ca,L in adult rat ventricular myocytes. Action potentials and I Ca,L were examined in the presence of 1 μM nadolol, a β-adrenergic antagonist, in myocytes internally dialyzed with Na+- and K+-free solutions (Cs+ and tetraethylammonium as substitutes). Phenylephrine (PE; 30 μM) increased the action potential duration measured at 25 and 70% of repolarization by 104 and 86%, respectively. In the perforated-patch configuration, PE elicited a transient decrease followed by a ∼60% increase in I Ca,L, whereas only the transient decrease in I Ca,L was observed in myocytes when the conventional whole cell configuration was used. The PE-induced increase in I Ca,L was reversibly blocked by 1 μM prazosin, an α1-adrenergic antagonist. These results suggest that α1-adrenergic stimulation enhances cardiac I Ca,L and that obligatory intracellular mediators for this action are lost during whole cell recordings.

scholarly journals Low-voltage triggering of Ca2+ release from the sarcoplasmic reticulum in cardiac muscle cells

2003 ◽  
Vol 285 (6) ◽  
pp. C1544-C1552 ◽  
Author(s):  
Fabien Brette ◽  
Jean-Yves Le Guennec ◽  
Ian Findlay
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Guinea Pig ◽  
Cardiac Muscle ◽  
Small Amplitude ◽  
Ventricular Myocytes ◽  
Low Voltage ◽  
Cell Voltage ◽  
Slip Mode ◽  
Cardiac Muscle Cells ◽  
Whole Cell

This study investigated the interaction between L-type Ca2+ current (ICaL) and Ca2+ release from the sarcoplasmic reticulum (SRCR) in whole cell voltage-clamped guinea pig ventricular myocytes. Quasiphysiological cation solutions (Nao+:KI+) were used for most experiments. In control conditions, there was no obvious interaction between ICaL and SRCR. In isoproterenol, activation of ICaL from voltages between -70 and -50 mV reduced the amplitude and accelerated the decay of the current. Short (50 ms), small-amplitude voltage steps applied 60 or 510 ms before stimulating ICaL inhibited and facilitated the current, respectively. These changes were blocked by ryanodine. Low-voltage activated currents such as T-type Ca2+ current, TTX-sensitive ICa (ICaTTX), or “slip mode” Ca2+ conductance via INa+ were not responsible for low-voltage SRCR. However, L-type Ca2+ currents could be distinguished at voltages as negative as -45 mV. It is concluded that in the presence of isoproterenol, Ca2+ release from the SR at negative potentials is due to activation of L-type Ca2+ channels.

L-type Ca2+ currents in ventricular myocytes from neonatal and adult rats

1998 ◽  
Vol 76 (9) ◽  
pp. 873-881 ◽  
Author(s):  
Yasuhiro Katsube ◽  
Hisashi Yokoshiki ◽  
Lam Nguyen ◽  
Masao Yamamoto ◽  
Nicholas Sperelakis
Keyword(s):  
Steady State ◽  
Voltage Clamp ◽  
Single Channel ◽  
Ventricular Myocytes ◽  
Cell Voltage ◽  
Fast Component ◽  
Whole Cell ◽  
Single Channel Recordings ◽  
Mode 2 ◽  
Adult Cells

Postnatal changes in the slow Ca2+ current (ICa(L)) were investigated in freshly isolated ventricular myocytes from neonatal (1-7 days old) and adult (2-4 months old) rats, using whole-cell voltage clamp and single-channel recordings. The membrane capacitance (mean ± SEM) averaged 23.2 ± 0.5 pF in neonates (n = 163) and 140 ± 4.1 pF in adults (n = 143). ICa(L) was measured as the peak inward current at a test potential of +10 mV (or +20 mV) by applying a 300-ms pulse from a holding potential of -40 mV; 1.8 mM Ca2+ was used as charge carrier. The basal ICa(L) density was 6.7 ± 0.2 pA/pF in neonatal and 7.8 ± 0.2 pA/pF in adult cells (p < 0.05). The time course of inactivation of the fast component (at +10 ms) was significantly longer in the neonatal (10.7 ± 1.4 ms) than in the adult (6.6 ± 0.4 ms) cells (p < 0.05). Ryanodine (10 muM) significantly increased this value to 18.0 ± 1.9 in neonate (n = 8) and to 17.7 ± 2.0 in adult (n = 9). For steady-state inactivation, the half-inactivation potential (Vh) was not changed in either group. For steady-state activation, Vh was 5.1 mV in the neonatal (n = 6) and -7.9 mV in the adult cells (n = 7). Single-channel recordings revealed that long openings (mode-2 behavior) were occasionally observed in the neonatal cells (11 events from 1080 traces / 11 cells), but not in the adult cells (400 traces / 4 cells). Slope conductance was 24 pS in both the neonatal and adult cells. Results in rat ventricular myocytes suggest the following: (i) the peak Ca2+ current density is already well developed in the neonatal period (being about 85% of the adult value); (ii) the fast component of inactivation is slower in neonates than in adults; and (iii) naturally occurring long openings are occasionally observed in the neonatal stage but not in the adult. Thus, the L-type Ca2+ channels of the neonate were slightly lower in density, were inactivated more slowly, and occasionally exhibited mode-2 behavior as compared with those of the adult.Key words: Ca2+ channels; neonatal heart cells; whole-cell voltage clamp; single-channel recordings; long openings of Ca2+ channels.

Reexamination of the Stoichiometry of Na+/Ca2+ Exchange with Whole-Cell Voltage Clamp of Guinea Pig Ventricular Myocytes

2006 ◽  
Vol 976 (1) ◽  
pp. 154-156 ◽  
Author(s):  
MASAMITSU HINATA ◽  
HISAO YAMAMURA ◽  
LIBING LI ◽  
YASUHIDE WATANABE ◽  
TOMOKAZU WATANO ◽  
...  
Keyword(s):  
Guinea Pig ◽  
Voltage Clamp ◽  
Ventricular Myocytes ◽  
Cell Voltage ◽  
Whole Cell ◽  
Whole Cell Voltage Clamp

scholarly journals Altered Na/Ca exchange distribution in ventricular myocytes from failing hearts

2016 ◽  
Vol 310 (2) ◽  
pp. H262-H268 ◽  
Author(s):  
Hanne C. Gadeberg ◽  
Simon M. Bryant ◽  
Andrew F. James ◽  
Clive H. Orchard
Keyword(s):  
Heart Failure ◽  
Ventricular Myocytes ◽  
Cell Voltage ◽  
Coronary Artery Ligation ◽  
Sham Operation ◽  
Ca Current ◽  
Artery Ligation ◽  
Whole Cell ◽  
Rat Hearts ◽  
T Tubules

In mammalian cardiac ventricular myocytes, Ca efflux via Na/Ca exchange (NCX) occurs predominantly at T tubules. Heart failure is associated with disrupted t-tubular structure, but its effect on t-tubular function is less clear. We therefore investigated t-tubular NCX activity in ventricular myocytes isolated from rat hearts ∼18 wk after coronary artery ligation (CAL) or corresponding sham operation (Sham). NCX current ( INCX) and l-type Ca current ( ICa) were recorded using the whole cell, voltage-clamp technique in intact and detubulated (DT) myocytes; intracellular free Ca concentration ([Ca]i) was monitored simultaneously using fluo-4. INCX was activated and measured during application of caffeine to release Ca from sarcoplasmic reticulum (SR). Whole cell INCX was not significantly different in Sham and CAL myocytes and occurred predominantly in the T tubules in Sham myocytes. CAL was associated with redistribution of INCX and ICa away from the T tubules to the cell surface and an increase in t-tubular INCX/ ICa density from 0.12 in Sham to 0.30 in CAL myocytes. The decrease in t-tubular INCX in CAL myocytes was accompanied by an increase in the fraction of Ca sequestered by SR. However, SR Ca content was not significantly different in Sham, Sham DT, and CAL myocytes but was significantly increased by DT of CAL myocytes. In Sham myocytes, there was hysteresis between INCX and [Ca]i, which was absent in DT Sham but present in CAL and DT CAL myocytes. These data suggest altered distribution of NCX in CAL myocytes.

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