Inhibitory effects of sevoflurane on pacemaking activity of sinoatrial node cells in guinea‐pig heart

Abstract

BACKGROUND AND PURPOSEThe volatile anaesthetic sevoflurane affects heart rate in clinical settings. The present study investigated the effect of sevoflurane on sinoatrial (SA) node automaticity and its underlying ionic mechanisms. EXPERIMENTAL APPROACHSpontaneous action potentials and four ionic currents fundamental for pacemaking, namely, the hyperpolarization-activated cation current (If), T-type and L-type Ca 2+ currents (ICa,T and ICa,L, respectively), and slowly activating delayed rectifier K + current (IKs), were recorded in isolated guinea-pig SA node cells using perforated and conventional whole-cell patch-clamp techniques. Heart rate in guinea-pigs was recorded ex vivo in Langendorff mode and in vivo during sevoflurane inhalation. KEY RESULTSIn isolated SA node cells, sevoflurane (0.12-0.71 mM) reduced the firing rate of spontaneous action potentials and its electrical basis, diastolic depolarization rate, in a qualitatively similar concentration-dependent manner. Sevoflurane (0.44 mM) reduced spontaneous firing rate by approximately 25% and decreased If, ICa,T, ICa,L and IKs by 14.4, 31.3, 30.3 and 37.1%, respectively, without significantly affecting voltage dependence of current activation. The negative chronotropic effect of sevoflurane was partly reproduced by a computer simulation of SA node cell electrophysiology. Sevoflurane reduced heart rate in Langendorff-perfused hearts, but not in vivo during sevoflurane inhalation in guinea-pigs. CONCLUSIONS AND IMPLICATIONSSevoflurane at clinically relevant concentrations slowed diastolic depolarization and thereby reduced pacemaking activity in SA node cells, at least partly due to its inhibitory effect on If, ICa,T and ICa,L. These findings provide an important electrophysiological basis of alterations in heart rate during sevoflurane anaesthesia in clinical settings. AbbreviationsAPA, action potential amplitude; APD, action potential duration; APD50, action potential duration measured from the peak to 50% repolarization; APD90, action potential duration measured from the peak to 90% repolarization; DDR, diastolic depolarization rate;

Ionic mechanisms underlying the negative chronotropic action of propofol on sinoatrial node automaticity in guinea pig heart

“…I Ca,T and I Ca,L were separated and identified by using different holding potentials of −90 and −60 mV and by performing subtraction of the current traces (Hagiwara et al ., ; Mangoni et al ., ; Kojima et al ., 2012; 2014). Figure shows the superimposed current traces for the voltage‐dependent Ca 2+ current ( I Ca , composed of I Ca,T and I Ca,L ), I Ca,L and I Ca,T , recorded before and after 5 min of exposure to 50 μM propofol at various test potentials in the same sinoatrial node cell.…”

“…Single sinoatrial node cells were obtained from the hearts of guinea pigs that had been deeply anaesthetized by an overdose of sodium pentobarbital (120 mg·kg −1 , i.p. ), using an enzymatic dissociation procedure similar to that described previously (Matsuura et al ., ; Kojima et al ., 2012; 2013; 2014).…”

“…Spontaneous action potentials and membrane currents were recorded using the amphotericin B‐perforated and ruptured patch‐clamp techniques, respectively. All recordings were conducted at 36 ± 1°C using an EPC‐8 patch‐clamp amplifier controlled by Patchmaster software (HEKA Elektronik, Lambrecht, Germany), as previously described (Kojima et al ., 2012; 2013; 2014). The current amplitude was expressed as the current density (pA·pF −1 ), obtained by normalizing the current to the cell capacitance.…”

“…ECG was recorded from the Langendorff‐perfused guinea pig hearts using a PowerLab data acquisition system and LabChart 7 software (ADInstruments, Castle Hill, Australia), as previously described (Kojima et al ., 2012; 2013; 2014). QT intervals were corrected (QTc) for the heart rate using Bazett's formula (Brouillette et al ., ): …”

“…There are a number of clinical observations showing that various general anaesthetics including volatile and intravenous anaesthetics, and opioids have considerably different effects on the heart rate (Ebert et al ., ; Kanaya et al ., ; Komatsu et al ., ). We have conducted a series of studies to elucidate the ionic, cellular and neuronal mechanisms underlying changes in the heart rate during administration of sevoflurane, desflurane and remifentanil using experimental animals (Kojima et al ., 2012; 2013; 2014). The intravenous general anaesthetic propofol (2,6‐diisopropylphenol) is widely used in the induction and maintenance of general anaesthesia and conscious sedation because of its favourable pharmacokinetic properties associated with a controllable anaesthetic state, smooth induction and fast awakening (Smith et al ., ).…”