Electrophysiological insights into the relationship between calcium dynamics and cardiomyocyte beating function in chronic hemodialysis treatment.

For patients in which the Ca2+ concentration of dialysis fluid is lower than that in plasma, chronic hemodialysis treatment often leads to cardiac beating dysfunction. By applying these conditions to an electrophysiological mathematical model, we evaluated the impact of body fluid Ca2+ dynamics during treatment on cardiomyocyte beating and, moreover, explored measures that may prevent cardiomyocyte beating dysfunction. First, Ca2+ concentrations in both plasma and interstitial fluid were decreased with treatment time, which induced both a slight decline in beating rhythm on a sinoatrial nodal cell and a wane in contraction force on a ventricular cell. These simulated results were in agreement with clinical observations. Next, a relationship between the intracellular Ca2+ concentration and ion current dynamics of ion transporters were examined to elucidate the mechanism underlying cardiomyocyte beating dysfunction. The inward current of the Na/Ca exchanger (NCX) increased with a decrease in Ca2+ concentration in interstitial fluid and induced a reduction in intracellular Ca2+ concentration during treatment. Furthermore, the decline in intracellular Ca2+ concentration reduced the contraction force. These findings implied that ion transport through the NCX is a dominant factor that induces cardiomyocyte beating dysfunction during hemodialysis. Finally, the replenishment of Ca2+ or application of an NCX inhibitor during treatment suppressed the decrease in intracellular Ca2+ concentration and contributed to the stabilization of cardiomyocyte beating function. In summary, the clinical implementation of hepatically cleared NCX inhibitor may be a suitable approach to improving the quality of life for patients on chronic hemodialysis.

The Impact of Potassium Dynamics on Cardiomyocyte Beating in Hemodialysis Treatment.

Background: Observational studies of intermittent hemodialysis therapy have reported that the excess decrease in K+ concentration in plasma (KP) during treatment is associated with the destabilization of cardiac function. Elucidating the mechanism by which the decrease in KP impairs myocardial excitation is indispensable for a deeper understanding of prescription design. Methods: In this study, by using an electrophysiological mathematical model, we investigated the relationship between KP dynamics and cardiomyocyte excitability for the first time. Results: The excess decrease in KP during treatment destabilized cardiomyocyte excitability through the following events: (1) a decrease in KP led to the prolongation of the depolarization phase of ventricular cells due to the reduced potassium efflux rate of the Kr channel, temporarily enhancing contraction force; (2) an excess decrease in KP activated the transport of K+ and Na+ through the funny channel in sinoatrial nodal cells, disrupting automaticity; (3) the excess decrease in KP also resulted in a significant decrease in the resting membrane potential of ventricular cells, causing contractile dysfunction. Avoiding an excess decrease in KP during treatment contributed to the maintenance of cardiomyocyte excitability. Conclusions: The results of these mathematical analyses showed that it is necessary to implement personal prescription or optimal control of K+ concentration in dialysis fluid based on predialysis KP from the perspective of regulatory science in dialysis treatment.

Experience with the JMS fully automated dialysis machine.

A fully automated dialysis machine has been developed and evaluated clinically. It uses highly pure dialysate (produced by a new dialysate cleaning system) instead of the conventional physiologic saline for the processes of priming, guiding blood to the dialysis machine, replenishing fluid, and returning the blood to the body. The piping for the dialysate is in the shape of a loop, and the dialyzer coupler has no mechanical parts that might become contaminated. As a result of these and certain other improvements in machine design, it is now possible to obtain reasonably clean dialysate. For the priming process, the machine uses a volume of up to 4 L of the dialysate after reverse filtration from the dialyzer. Most foreign matter or eluates can be removed from the dialyzer and the blood channels. Before blood is guided out of the body into the dialysis system, the needles inserted in the artery and vein are simultaneously connected to the blood channel, and the dialysate remaining in the channel is removed from the dialyzer. If the patient's blood pressure falls during dialysis, the dialysate can be replenished at any desired flow rate for reverse filtration. Blood return can be started automatically when the planned dialysis time has elapsed and the target water volume has been removed. The cleaned dialysate is infused from the dialyzer into the blood channel by reverse filtration to allow the blood to be returned to the body via both the artery and the vein at the same time. A total of 216 units of this fully automated dialysis machine have been placed in service at two of our facilities. During the 6 month period beginning in July 2001, they were used for 40,000 hemodialysis sessions in 516 patients. During the dialysate preparation process, the endotoxin levels in the reverse osmosis (RO) water, prefilter dialysate, and reverse filtered dialysate were all less than 1 EU/L. The time required to guide blood into the dialyzer (n = 39) decreased from the 4.6 +/- 1.4 minutes with the conventional machines to 3.2 +/- 0.6 minutes with the new machine (p < 0.01). The time required to return blood to the body also decreased from 8.6 +/- 2.2 minutes with the conventional machines to 6.8 +/- 0.7 minutes with the new machine (n = 34). No mechanical trouble was encountered with the fully automated dialysis machine units during the 40,000 hemodialysis sessions, and the workload of the dialysis unit staff in terms of the time needed to guide out and return blood to the body was significantly reduced. Because the machine simplifies the maneuvers required during hemodialysis, it is expected to contribute greatly to preventing medical accidents and in hospital infections associated with hemodialysis.

A forskolin derivative, colforsin daropate hydrochloride, inhibits rat mesangial cell mitogenesis via the cyclic AMP pathway.

A forskolin derivative, colforsin daropate hydrochloride (CDH), has been introduced as an inotropic agent that acts directly on adenylate cyclase to increase intracellular cyclic AMP (cAMP) levels and ventricular contractility, resulting in positive inotropic activity. We investigated the effects of CDH on rat mesangial cell (MC) proliferation. CDH (10(-7)-10(-5) mol/l) inhibited [(3)H]thymidine incorporation into cultured rat MCs in a concentration-dependent manner. CDH (10(-7)-10(-5) mol/l) also decreased cell numbers in a similar manner, and stimulated cAMP accumulation in MCs in a concentration-dependent manner. A protein kinase A inhibitor, H-89, abolished the inhibitory effects of CDH on MC mitogenesis. These findings suggest that CDH would inhibit the proliferation of rat MCs via the cAMP pathway.

Flavoxobin, a serine protease from Trimeresurus flavoviridis (habu snake) venom, independently cleaves Arg726-Ser727 of human C3 and acts as a novel, heterologous C3 convertase.

We have recently shown that crude Trimeresurus flavoviridis (habu snake) venom has a strong capability for activating the human alternative complement system. To identify the active component, the crude venom was fractionated and purified by serial chromatography using Sephadex G-100, CM-cellulose C-52, diethylaminoethyl-Toyopearl 650M, and Butyl-Toyopearl, and the active fractions were evaluated by the C3a-releasing and soluble membrane attack complex-forming activities. Two peak fractions with the highest activities were detected after gel filtration and ion exchange chromatography, and the first fraction was purified to homogeneity. The homogeneous protein was examined for its N-terminal amino acid sequence by Edman degradation. The determined sequence of 25 amino acids completely coincided with that of a previously reported serine protease with coagulant activity, flavoxobin, purified from the same snake venom. To elucidate the molecular mechanism of the complement activation, the reactive products of the mixture of the purified human C3 and flavoxobin were examined by sodium dodecyl sulphate-polyacrylamide gel electrophoresis. The digesting pattern revealed that flavoxobin cleaves the alpha chain of the C3 molecule into two fragments. The N-terminal amino acid sequences for the remnant fragments of C3 disclosed that flavoxobin severs the human C3 at the Arg726-Ser727 site to form C3b and C3a the way C3bBb, the human alternative C3 convertase, does. In conclusion, flavoxobin acts as a novel, heterologous C3 convertase that independently cleaves human C3 and kick-starts the complement cascade.