Postnatal developmental changes in the sensitivity of L-type Ca2+ channel to inhibition by verapamil in a mouse heart model.

BackgroundIn the clinical setting, verapamil is contraindicated in neonates and infants, because of the perceived risk of hypotension or bradyarrhythmia. However, it remains unclear whether there is an age-dependent difference in the sensitivity of cardiac L-type Ca2+ channel current (ICa,L) to inhibition by verapamil.MethodsVentricular myocytes were enzymatically dissociated from the hearts of six different age groups (0, 7, 14, 21, 28 days, and 10-15 weeks) of mice, using a similar Langendorff-perfusion method. Whole-cell patch-clamp technique was applied to examine the sensitivity of ICa,L to inhibition, by three classes of structurally different L-type Ca2+ channel antagonists.ResultsVerapamil, nifedipine, and diltiazem concentration-dependently blocked the ventricular ICa,L in all six age groups. However, although nifedipine and diltiazem blocked ventricular ICa,L with a similar potency in all age groups, verapamil more potently blocked ventricular ICa,L in day 0, day 7, day 14, and day 21 mice, than in day 28, and 10-15-week mice.ConclusionIn a mouse heart model, ventricular ICa,L before the weaning age (~21 days of age) exhibited a higher sensitivity to inhibition by verapamil than that after the weaning age, which may explain one possible mechanism associated with the development of verapamil-induced hypotension in human neonates and infants.

A simple antegrade perfusion method for isolating viable single cardiomyocytes from neonatal to aged mice.

The aim of this study was to establish a simple and reproducible antegrade perfusion method for isolating single viable mouse heart cells and to determine the standard practical protocols that are appropriate for mice of various ages. Antegrade perfusion was performed by injecting perfusate from near the apex of the left ventricle of the excised heart, the aorta of which was clamped, using an infusion pump. This could thoroughly perfuse the myocardium through the coronary circulation. All procedures were carried out on a prewarmed heater mat under a microscope, which allows for the processes of injection and perfusion to be monitored. With appropriate adjustment of the size of the injection needle, the composition and amount of enzyme solution and the perfusion flow rate, this antegrade perfusion method could be applied to the hearts of neonatal to aged mice. We examined the morphological characteristics and electrophysiological properties of the isolated ventricular and atrial myocytes and found that these cells were mostly identical to those obtained with the traditional Langendorff-based retrograde perfusion method. Interstitial nonmyocytes, such as cardiac progenitor cells, were also isolated simultaneously from the supernatant fraction of the centrifugation, similar to the retrograde perfusion method. The results suggest that single heart cells can be well isolated with high degree of quality by the present antegrade perfusion method, regardless of the age of the mouse.

Chondroitin sulfate protects vascular endothelial cells from toxicities of extracellular histones.

Extracellular histones induce lethal thrombosis by promoting platelet aggregation, neutrophil migration, and cell injuries. Heparin, which has negative charges, can bind to extracellular histones; however, heparin strongly inhibits the activation of coagulation. Since chondroitin sulfate (CS) shows less effect on the coagulation system than heparin does, CS has the potential to become an effective drug for lethal thrombosis with high risk of bleeding. To elucidate the therapeutic mechanisms of CS in lethal thrombosis, we investigated the interaction between CS and extracellular histones. Mouse vascular endothelial cells were incubated with histones in the presence of heparin or CS, and the expression of caspase-3/7 was measured. The interactions between histones and heparin or CS were measured by surface plasmon resonance analysis. Vascular permeability, platelet counts, liver and renal functions, and coagulation times were evaluated in an in vivo assay. The apoptosis induced by histones was inhibited by treatment with heparin or CS. Heparin and CS showed strong binding to histones and inhibited vascular hyperpermeability. The platelet counts as well as liver and renal functions were not decreased by the treatment with heparin or CS. Moreover, CS showed less effect on the coagulation system than heparin did. These results suggested that CS can be a novel agent for lethal thrombosis with the risk for hemorrhage. Since vascular endothelial cell injuries occur at an early stage of lethal thrombosis, administration of CS might be a useful approach.

Complement component 5 promotes lethal thrombosis.

Extracellular histones promote platelet aggregation and thrombosis; this is followed by induction of coagulation disorder, which results in exhaustion of coagulation factors. Complement component 5 (C5) is known to be associated with platelet aggregation and coagulation system activation. To date, the pathological mechanism underlying liver injury has remained unclear. Here, we investigated whether C5 promotes liver injury associated with histone-induced lethal thrombosis. C5-sufficient and C5-deficient mice received single tail vein injections of purified, unfractionated histones obtained from calf thymus (45-75 µg/g). Subsequently, the mice were monitored for survival for up to 72 h. Based on the survival data, the 45 µg/g dose was used for analysis of blood cell count, liver function, blood coagulation ability, and promotion of platelet aggregation and platelet/leukocyte aggregate (PLA) production by extracellular histones. C5-deficient mice were protected from lethal thrombosis and had milder thrombocytopenia, consumptive coagulopathy, and liver injury with embolism and lower PLA production than C5-sufficient mice. These results indicate that C5 is associated with coagulation disorders, PLA production, and embolism-induced liver injury. In conclusion, C5 promotes liver injury associated with histone-induced lethal thrombosis.