Effects of norepinephine, calcium, and rate of discharge on 42K movements in canine cardiac Purkinje fibers

Ionized calcium level at emergency department arrival is associated with return of spontaneous circulation in out-of-hospital cardiac arrest

BACKGROUND

Calcium level is associated with sudden cardiac death based on several cohort studies. However, there is limited evidence on the association between ionized calcium, active form of calcium, and resuscitation outcome. This study aimed to evaluate the potential role of ionized calcium in predicting resuscitation outcome in patients with out-of-hospital cardiac arrest.

METHODS

We analyzed the Korean Cardiac Arrest Research Consortium data (KoCARC) registry, a web-based multicenter registry that included 65 participating hospitals throughout the Republic of Korea. The patients with out-of-hospital cardiac arrest over 19 years old and acquired laboratory data including calcium, ionized calcium, potassium, phosphorus, creatinine, albumin at emergency department (ED) arrival were included. The primary outcome was successful rate of return of spontaneous circulation (ROSC) and the secondary outcomes were survival hospital discharge and favorable neurological outcome (cerebral performance category 1 or 2) at hospital discharge.

RESULTS

Eight-hundred and eighty-three patients were enrolled in the final analysis and 448 cases (54%) had ROSC. In multivariable logistic regression analysis, ionized calcium level was associated with ROSC (odds ratio, 1.77; 95% CI1.28-2.45; p = 0.001) even though calcium level was not associated with ROSC (odds ratio, 0.87; 95% CI 0.70-1.08; p = 0.199). However, ionized calcium level was not associated with survival discharge (odds ratio, 0.99; 95% CI 0.72-1.36; p = 0.948) or favorable neurologic outcome (odds ratio, 0.45; 95% CI 0.03-6.55, p = 0.560).

CONCLUSION

A high ionized calcium level measured during cardiopulmonary resuscitation was associated with an increased likelihood of ROSC.

Cardiac ionic currents and acute ischemia: from channels to arrhythmias

The aim of this review is to provide basic information on the electrophysiological changes during acute ischemia and reperfusion from the level of ion channels up to the level of multicellular preparations. After an introduction, section II provides a general description of the ion channels and electrogenic transporters present in the heart, more specifically in the plasma membrane, in intracellular organelles of the sarcoplasmic reticulum and mitochondria, and in the gap junctions. The description is restricted to activation and permeation characterisitics, while modulation is incorporated in section III. This section (ischemic syndromes) describes the biochemical (lipids, radicals, hormones, neurotransmitters, metabolites) and ion concentration changes, the mechanisms involved, and the effect on channels and cells. Section IV (electrical changes and arrhythmias) is subdivided in two parts, with first a description of the electrical changes at the cellular and multicellular level, followed by an analysis of arrhythmias during ischemia and reperfusion. The last short section suggests possible developments in the study of ischemia-related phenomena.

Mechanisms by which calcium modulates diastolic depolarization in sheep cardiac Purkinje fibers

The mechanisms by which calcium modulates diastolic depolarization (DD) in sheep cardiac Purkinje fibers were studied in vitro. Increasing [Ca]o from 2.7 mM to 10.8 mM increased both the slope and amplitude of DD, induced oscillatory potentials (V(os)), and prolonged depolarization (V(ex)). The steepening of DD occurred even in the absence of an obvious V(os). The increase in DD amplitude was due both to an increase in the maximum diastolic potential and to a less negative steady-state level. At constant [Ca]o, increasing the driving rate had effects similar to those induced by increasing [Ca]o. The increase in DD slope and amplitude was least at the slowest rates and leveled off at the fastest rates in high [Ca]o. Lowering [Ca]o decreased DD slope and amplitude, but spontaneous activity could be present during interruption of the drive. In slowly driven fibers, increasing [Ca]o to 10.8 mM initially shifted the maximum diastolic potential and steady state DD to more negative values, and subsequently shifted the latter (but not the former) to less negative values. On recovery, a transient depolarization occurred. Quiescent fibers exposed to high [Ca]o also underwent a transient hyperpolarization and a subsequent depolarization, whereas reciprocal effects occurred when [Ca]o was lowered. It is concluded that [Ca]o modulates DD through several different mechanisms and that most (but not all) modifications induced are brought about by changes in [Ca]i.

Do calcium-activated potassium channels exist in the heart?

Changes of intracellular Ca concentration in cardiac muscle have significant effects on transmembrane currents and many of these effects can be accounted for by postulating the existence of Ca-activated K channels in the heart. However, the evidence that such channels exist is equivocal. This is partly because of technical problems, for example the difficulty of identifying an individual ionic current amongst the many currents that exist in the heart. An additional problem, however, is posed by the fact that other currents may also be modulated by Ca ions. It is important therefore to distinguish between these currents and those caused by Ca-activated, K-specific channels. In this review we consider the evidence for Ca activated currents in the heart and, in particular, we discuss whether or not these currents are carried exclusively by K ions.

Effects of epinephrine on the electrophysiologic properties of Purkinje fibers surviving myocardial infarction

The electrophysiologic effects of epinephrine on canine subendocardial Purkinje fibers were examined 24 hours after two-stage ligation of the left anterior descending coronary artery. Transmembrane action potential were monitored simultaneously in noninfarcted (NZ) and infarcted (IZ) zones during epinephrine superfusion at 37 degrees C. Epinephrine (10(-8) M to 10(-5) M) induced dose-dependent increases in maximum rate of phase O depolarization (Vmax), action potential amplitude (APA), and maximum diastolic potential (MDP) in both NZ and IZ. Epinephrine consistently shortened effective refractory period (ERP) in both regions No significant change in action potential duration (APD) was noted at either 50% or 90% repolarization. Impulse conduction through the NZ and into the IZ was significantly improved, as indicated by an increased maximum follow-rate in each region at 10(-6) and 10(-5) M epinephrine. The IZ fibers showed a marked hypersensitivity to this agent, in that responses were particularly pronounced in the IZ vs the NZ in terms of both absolute and percentage changes. The effects of epinephrine on Vmax, MDP, APA, and ERP were generally reversed by propranolol, while remaining relatively unaffected by phentolamine, suggesting a beta-adrenergic mechanism. Increased stimulation of ventricular beta-adrenoceptors in the period 16 to 72 hours after myocardial infarction may influence ventricular vulnerability to "late-phase" arrhythmias through nonuniform effects in Purkinje fibers.

Actions of prenalterol, a new cardioselective beta1-agonist, terbutaline and isoprenaline on electrophysiological and mechanical parameters of guinea pig atrial and papillary muscles

The electrophysiological and mechanical effects of prenalterol on the isolated guinea pig atrial trabeculae and papillary muscles were compared with those of terbutaline and isoprenaline. Isoprenaline was the most potent of the drugs tested on all parameters studied. Prenalterol, on the other hand, failed to induce any changes in the atrial action potentials. The action potential duration was shortened in the atrial trabeculae by terbutaline and isoprenaline. All three substances shortened the action potential in the papillary muscles. In addition, isoprenaline increased the plateau height, and like terbutaline, increased the rate of repolarization during phase 3. Neither prenalterol nor terbutaline changed the effective refractory period in the atrial trabeculae whereas isoprenaline shortened it. All three substances shortened this parameter in the papillary muscles. The developed force and the rate of developed force were increased by all three substances. In addition, the total twitch duration was decreased.

Changes in 42K efflux produced by alterations in transmembrane calcium movements in turtle cardiac pace-maker tissue

1. 42K efflux has been measured from small strips of turtle sinus venosus which were electrically paced. Three different procedures for altering transmembrane calcium influx have been utilized to test whether changes in 42K efflux may be modulated by changes in intracellular calcium levels. 2. No significant changes in the 42K fractional escape rate (FER) were observed when external calcium was reduced to O mM or increased to 4 x normal (10 mM). In these experiments extracellular divalent cation concentration was held constant by adding or removing magnesium ions. 3. Application of 10 mM-Ba2+ also failed to alter 42K FER consistently. In red blood cells and snail neurones addition of barium ions has been shown to reduce significantly the calcium-mediated potassium current. 4. A tenfold increase in pacing rate (0.5-5 Hz) resulted in an augmented 42K FER, but repetition of this rate change in O mM-Ca2+ indicated that this increase in 42K FER was not strongly dependent on the amount of calcium entry. 5. Attempts to load the pace-maker cells with calcium by using the ionophore A23187 (10 micrograms ml . -1 of 2.0 x 10(-5) M) consistently resulted in very large increases in 42K FER. However, this effect (i) was blocked by atropine and (ii) was markedly reduced by pretreating the tissues with hemicholinium, indicating that A23187-induced release of acetylcholine from the endogenous nerve terminals was responsible for the observed increase in 42K FER. 6. In summary, three different experimental tests indicate that the majority of the 42K efflux is not tightly linked to transmembrane calcium movement in sinus venosus pace-maker tissue.

Voltage-clamp investigations of membrane currents underlying pace-maker activity in rabbit sino-atrial node

1. Small preparations of spontaneously beating rabbit sino-atrial node have been investigated using the two micro-electrode voltage-clamp technique. 2. Hyperpolarizing clamp pulses given from holding potentials of about -45 mV reveal a time-dependent change of a membrane current, if, which is shown to overlap the pace-maker range (-65 mV to -45 mV) for these preparations. 3. The changes in if are shown to be quite distinct from the de-activation of the time-dependent outward current, iK. 4. The time-dependent changes of the if system increase during adrenaline application and therefore contribute to the chronotropic action of adrenaline on the heart. 5. Evidence for a link between slow inward current (iSi) and time-dependent outward current (iK) in rabbit sino-atrial node is presented and assessed.