Ca2+ current and Ca2+ transients under action potential clamp in guinea pig ventricular myocytes

Arreola, Jorge; Dirksen, Robert T.; Shieh, Ru‐Chi; Williford, Daniel J.; Sheu, Shey‐Shing

doi:10.1152/ajpcell.1991.261.2.c393

Cited by 102 publications

(41 citation statements)

References 28 publications

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“…The use of the AP clamp technique has provided some unique insight into the time course of I Ca under more physiological conditions. [11][12][13] 21,23 Initially, standard I-V curves were assessed with square voltage-clamp pulses (holding potential, E H ϭϪ70 mV, 200-ms steps to Ϫ20 to ϩ40 mV). Then, AP waveforms recorded in current clamp were used for trains of AP clamps.…”

Section: Abstract-camentioning

confidence: 99%

Ca ²⁺ Influx Through Ca ²⁺ Channels in Rabbit Ventricular Myocytes During Action Potential Clamp

Puglisi

Yuan

Bassani

et al. 1999

Circulation Research

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Abstract-Ca2ϩ influx via Ca 2ϩ current (I Ca ) during the action potential (AP) was determined at 25°C and 35°C in isolated rabbit ventricular myocytes using AP clamp. Contaminating currents through Na ϩ and K ϩ channels were eliminated by using Na ϩ -and K ϩ -free solutions, respectively. DIDS (0.2 mmol/L) was used to block Ca 2ϩ -activated chloride current (I Cl(Ca) ). When the sarcoplasmic reticulum (SR) was depleted of Ca 2ϩ by preexposure to 10 mmol/L caffeine, total Ca 2ϩ entry via I Ca during the AP was Ϸ12 mol/L cytosol (at both 25°C and 35°C). Similar Ca 2ϩ influx at 35°C and 25°C resulted from a combination of higher and faster peak I Ca , offset by more rapid I Ca inactivation at 35°C. During repeated AP clamps, the SR gradually fills with Ca 2ϩ , and consequent SR Ca 2ϩ release accelerates I Ca inactivation during the AP. During APs and contractions in steady state, total Ca 2ϩ influx via I Ca was reduced by Ϸ50% but was again unaltered by temperature (5.6Ϯ0.2 mol/L cytosol at 25°C, 6.0Ϯ0.2 mol/L cytosol at 35°C). Thus, SR Ca 2ϩ release is responsible for sufficient I Ca inactivation to cut total Ca 2ϩ influx in half. However, because of the kinetic differences in I Ca , the amount of Ca 2ϩ influx during the first 10 ms, which presumably triggers SR Ca 2ϩ release, is much greater at 35°C. I Ca during a first pulse, given just after the SR was emptied with caffeine, was subtracted from I Ca during each of 9 subsequent pulses, which loaded the SR. These difference currents reflect I Ca inactivation due to SR Ca 2ϩ release and thus indicate the time course of local [Ca 2ϩ ] in the subsarcolemmal space near Ca 2ϩ channels produced by SR Ca 2ϩ release (eg, maximal at 20 ms after the AP activation at 35°C). Furthermore, the rate of change of this difference current may reflect the rate of SR Ca 2ϩ release as sensed by L-type Ca 2ϩ channels. These results suggest that peak SR Ca 2ϩ release occurs within 2.5 or 5 ms of AP upstroke at 35°C and 25°C, respectively. I Cl(Ca) might also indicate local [Ca 2ϩ ], and at 35°C in the absence of DIDS (when I Cl(Ca) is prominent), peak I Cl(Ca) also occurred at a time comparable to the peak I Ca difference current. We conclude that SR Ca 2ϩ release decreases the Ca 2ϩ influx during the AP by Ϸ50% (at both 25°C and 35°C) and that changes in I Ca (and I Cl(Ca) ), which depend on SR Ca 2ϩ release, provide information about local subsarcolemmal [Ca 2ϩ ]. The full text of this article is available at http://www.circresaha.org. (Circ Res. 1999;85:e7-e16.)

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Section: Abstract-camentioning

confidence: 99%

Ca ²⁺ Influx Through Ca ²⁺ Channels in Rabbit Ventricular Myocytes During Action Potential Clamp

Puglisi

Yuan

Bassani

et al. 1999

Circulation Research

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“…This technique has been successfully applied to the study of I Ca in guinea pig ventricular myocytes [2] and the role of I K1 in the plateau and repolarization phases of the rabbit AP [32]. Bouchard et al [9] used this ap- proach to investigate the effect of AP prolongation upon I Ca .…”

Section: The Ap Voltage-clamp Techniquementioning

confidence: 99%

Influence of postnatal changes in action potential duration on Na-Ca exchange in rabbit ventricular myocytes

Haddock

Artman

Coetzee

1998

Pfl�gers Archiv European Journal of Physiology

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Cardiac Na-Ca exchanger (NCX) expression and current density are significantly greater in newborn rabbit hearts compared with adults. However, the relatively short action potential (AP) at birth may limit the impact of increased NCX expression by diminishing Ca2+ entry via Na-Ca exchange current (INaCa). To address the interdependence of AP duration and NCX activity, we voltage-clamped newborn (NB, 1-5 day), juvenile (JV, 10-14 day) and adult (AD) rabbit myocytes with a series of APs of progressively increasing duration (APD90: 108-378 ms) under nominally chloride-free conditions. In each age group we quantified an increase in outward (QExout) and inward (QExin) Ni2+-sensitive charge movement in response to AP prolongation. QExout and QExin measured during age-appropriate APs declined postnatally [QEXout: NB (2 day) 0.19 +/- 0.02, JV (10 day) 0.10 +/- 0.01, AD 0.04 +/- 0.002; QEXin: NB -0. 2 +/- 0.01, JV -0.11 +/- 0.02; AD -0.04 +/- 0.003 pC/pF] despite the significantly shorter APD90 of newborn myocytes (NB 122 +/- 10; AD 268 +/- 22 ms). When Ca2+ fluxes by other transport pathways were blocked with nifedipine, ryanodine and thapsigargin, age-appropriate APs elicited contractions in NB and JV but not AD myocytes (NB 4.8 +/- 0.5, JV 1.2 +/- 0.3% resting length). These data demonstrate that a shorter AP does not negate the impact of increased NCX expression at birth.

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“…In the present study, we have used the "AP clamp" technique (e.g. [1,5,9,15]) to measure directly the time course and voltage dependence of HERG current during the ventricular AP. We had two additional aims: first, to investigate the underlying basis for the voltage dependence of HERG current during the AP.…”

Section: Introductionmentioning

confidence: 99%

Time course and voltage dependence of expressed HERG current compared with native ”rapid" delayed rectifier K current during the cardiac ventricular action potential

Hancox¹,

Levi²,

Witchel³

1998

Pfl�gers Archiv European Journal of Physiology

114

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It is widely believed that HERG (human ether-a-go-go-related gene) encodes the major subunit of the cardiac "rapid" delayed rectifier K channel. The aims of the present study were threefold: (1) to record directly the time course and voltage dependence of expressed HERG current in a mammalian cell line, during an imposed ventricular action potential (AP); (2) to compare this with native rapid delayed rectifier current (IKr) elicited by applying an AP command to isolated guinea-pig ventricular myocytes; (3) to provide mechanistic information regarding the profile of HERG/IKr during the AP. We used the AP clamp technique and conventional whole-cell patch-clamp recordings at 32-34 degreesC. HERG was transiently expressed in Chinese hamster ovary (CHO) cells. There was an outward current in transfected CHO cells, which developed progressively during the AP plateau and slow repolarisation phase. The instantaneous current-voltage (I-V) relation for both leak-subtracted HERG current (n=10) and E-4031-sensitive current (n=6) during AP repolarisation was maximal between -30 mV and -40 mV. The conductance-voltage (G-V) relation was maximal at potentials between -60 and -75 mV. A similar voltage dependence for HERG current was observed during a descending ramp from +60 to -80 mV (n=5), but not during either an ascending ramp (n=5), or a reversed AP waveform (n=8). These data suggest that instantaneous HERG current during the AP does not depend on the instantaneous command voltage alone, but upon the previous voltages during the applied waveform. The time course of activation of HERG current at potentials near the AP plateau was rapid. Tail currents recorded on premature repolarisation at different time points in the AP showed directly that HERG also activates rapidly during the AP. The I-V profiles of fully activated HERG and of current during the AP were very similar. IKr from guinea-pig ventricular myocytes was measured as E-4031-sensitive current during the AP clamp command. The current had a similar I-V and G-V profile to HERG current in CHO cells. These data indicate that HERG current and native IKr are similar during an applied AP waveform. Activation of HERG is rapid during the AP. However, due to rapid inactivation relatively little current flows until the potential becomes less positive than 0 mV. The removal of inactivation then allows more current to flow, giving rise to the distinct instantaneous I-V profile during the AP. The correlation between the voltage dependence of HERG during the AP and the fully activated I-V relation indicates that the contribution of HERG/IKr to AP repolarisation is more significantly determined by the open-channel I-V relation, than the precise activation time course of the current.

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Ca2+ current and Ca2+ transients under action potential clamp in guinea pig ventricular myocytes

Cited by 102 publications

References 28 publications

Ca ²⁺ Influx Through Ca ²⁺ Channels in Rabbit Ventricular Myocytes During Action Potential Clamp

Ca ²⁺ Influx Through Ca ²⁺ Channels in Rabbit Ventricular Myocytes During Action Potential Clamp

Influence of postnatal changes in action potential duration on Na-Ca exchange in rabbit ventricular myocytes

Time course and voltage dependence of expressed HERG current compared with native ”rapid" delayed rectifier K current during the cardiac ventricular action potential

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Ca2+ current and Ca2+ transients under action potential clamp in guinea pig ventricular myocytes

Cited by 102 publications

References 28 publications

Ca 2+ Influx Through Ca 2+ Channels in Rabbit Ventricular Myocytes During Action Potential Clamp

Ca 2+ Influx Through Ca 2+ Channels in Rabbit Ventricular Myocytes During Action Potential Clamp

Influence of postnatal changes in action potential duration on Na-Ca exchange in rabbit ventricular myocytes

Time course and voltage dependence of expressed HERG current compared with native ”rapid" delayed rectifier K current during the cardiac ventricular action potential

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About

Ca ²⁺ Influx Through Ca ²⁺ Channels in Rabbit Ventricular Myocytes During Action Potential Clamp

Ca ²⁺ Influx Through Ca ²⁺ Channels in Rabbit Ventricular Myocytes During Action Potential Clamp