Lipopolysaccharide prolongs action potential duration in HL-1 mouse cardiomyocytes

Abstract

Wondergem R, Graves BM, Li C, Williams DL. Lipopolysaccharide prolongs action potential duration in HL-1 mouse cardiomyocytes. Am J Physiol Cell Physiol 303: C825-C833, 2012. First published August 15, 2012; doi:10.1152/ajpcell.00173.2012.-Sepsis has deleterious effects on cardiac function including reduced contractility. We have shown previously that lipopolysaccharides (LPS) directly affect HL-1 cardiac myocytes by inhibiting Ca 2ϩ regulation and by impairing pacemaker "funny" current, I f. We now explore further cellular mechanisms whereby LPS inhibits excitability in HL-1 cells. LPS (1 g/ml) derived from Salmonella enteritidis decreased rate of firing of spontaneous action potentials in HL-1 cells, and it increased their pacemaker potential durations and decreased their rates of depolarization, all measured by whole cell current clamp. LPS also increased action potential durations and decreased their amplitude in cells paced at 1 Hz with 0.1 nA, and 20 min were necessary for maximal effect. LPS decreased the amplitude of a rapidly inactivating inward current attributed to Na ϩ and of an outward current attributed to K ϩ ; both were measured by whole cell voltage clamp. The K ϩ currents displayed a resurgent outward tail current, which is characteristic of the rapid delayed-rectifier K ϩ current, IKr. LPS accordingly reduced outward currents measured with pipette Cs ϩ substituted for K ϩ to isolate IKr. E-4031 (1 M) markedly inhibited IKr in HL-1 cells and also increased action potential duration; however, the direct effects of E-4031 occurred minutes faster than the slow effects of LPS. We conclude that LPS increases action potential duration in HL-1 mouse cardiomyocytes by inhibition of IKr and decreases their rate of firing by inhibition of INa. This protracted time course points toward an intermediary metabolic event, which either decreases available mouse ether-a-go-go (mERG) and Na ϩ channels or potentiates their inactivation.delayed rectifier K ϩ current; patch-clamp electrophysiology; Salmonella enteritidis; E-4031 SEPSIS IS A COMPLEX CLINICAL problem that can progress into multiorgan dysfunction syndrome (MODS) and death. At least one-half of the high mortality rates of severe-sepsis, sepsis, and MODS result from cardiovascular failure (27). Approximately 40% of patients in septic shock also experience myocardial dysfunction (36, 44), which comprises reduced systolic contractility, impaired diastolic relaxation, and ventricular dilatation. The initial clinical pattern, however, ironically is termed "hyperdynamic," because it often presents with high cardiac output, elevated heart rate, and vasodilatation of the dermis (27). This is attributable in part to the volume loading that is frequently the initial treatment for septic shock patients to maintain cardiac output and organ perfusion (15, 28). As is often the case in the complexity of sepsis, the prevailing symptoms can mask organ and system failure occurring at a deeper level in the clinical spectrum.The most prevalent sign of myocardial depressio...

The Sick and the Weak: Neuropathies/Myopathies in the Critically Ill

“…Reduction in the rate of action potential rise suggested the etiology of reduced cardiac excitability was a reduction in sodium current. The in vivo data fit well with an earlier in vitro study in which application of LPS to mouse cardiomyocytes reduced excitability (785). Although the mechanism underlying the reduction in sodium current is not known, these data are consistent with an acquired sodium channelopathy in heart that affects the Na v 1.5 Na ϩ channel isoform.…”

Overexpression of the Large-Conductance, Ca2+-Activated K+ (BK) Channel Shortens Action Potential Duration in HL-1 Cardiomyocytes

“…We used the HL-1 cell model in this study because it displays a combination of important assets. HL-1 cells are a stable expression model, exhibit ease of transfection unlike primary cardiac myocytes, are amenable to patch-clamp and current-clamp studies, and express a complement of ion channels on the cell surface including voltage gated Na + , Ca 2+ and K + channels that resemble the ion channel types found in primary cultures of mammalian cardiac cells [ 7 , 9 , 13 , 24 , 34 , 35 ]. Nonetheless, we acknowledge that there are significant limitations related to our choice of the HL-1 cell line.…”

9-Phenanthrol and flufenamic acid inhibit calcium oscillations in HL-1 mouse cardiomyocytes

“…The latter has long been attributed to the “funny current,” I f , and associated HCN channels in HL-1 cells [21] as well as well as isolated sinoatrial node cells [37]. However, our prior study of HL-1 cells [22] demonstrated I f to be activated primarily at membrane potentials more negative than the -60 to -65 mV found to be the maximal diastolic potential in the HL-1 cells [22, 23]. TRPM4 on the other hand is activated by depolarization [4] and is expressed in mouse sinoatrial node cells [10].…”

“…About 30-40% of HL-1 cells display [Ca 2+ ] i oscillations that result in part from spontaneous action potentials, which are generated by the depolarizing I f attributed to hyperpolarization-activated cyclic nucleotide-gate (HCN) ion channels [21, 22]. We have shown that lipopolysaccharides directly inhibit HL-1 cell [Ca 2+ ] i oscillations as well as I f [22] and extend duration of the action potential [23]. We also have shown that activation of I f in HL-1 cells occurs typically at voltages more negative than the resting membrane potential of -60 mV [22].…”