Two potential calmodulin-binding sequences in the ryanodine receptor contribute to a mobile, intra-subunit calmodulin-binding domain

Calmodulin (CaM), a 16 kDa ubiquitous calcium-sensing protein, is known to bind tightly to the calcium release channel/ryanodine receptor (RyR), and modulate RyR function. CaM binding studies using RyR fragments or synthetic peptides have revealed the presence of multiple, potential CaM-binding regions in the primary sequence of RyR. In the present study, we inserted GFP into two of these proposed CaM-binding sequences and mapped them onto the three-dimensional structure of intact cardiac RyR2 by cryo-electron microscopy. Interestingly, we found that the two potential CaM-binding regions encompassing, Arg3595 and Lys4269, respectively, are in close proximity and are adjacent to the previously mapped CaM-binding sites. To monitor the conformational dynamics of these CaM-binding regions, we generated a fluorescence resonance energy transfer (FRET) pair, a dual CFP- and YFP-labeled RyR2 (RyR2R3595-CFP/K4269-YFP) with CFP inserted after Arg3595 and YFP inserted after Lys4269. We transfected HEK293 cells with the RyR2R3595-CFP/K4269-YFP cDNA, and examined their FRET signal in live cells. We detected significant FRET signals in transfected cells that are sensitive to the channel activator caffeine, suggesting that caffeine is able to induce conformational changes in these CaM-binding regions. Importantly, no significant FRET signals were detected in cells co-transfected with cDNAs encoding the single CFP (RyR2R3595-CFP) and single YFP (RyR2K4269-YFP) insertions, indicating that the FRET signal stemmed from the interaction between R3595-CFP and K4269-YFP that are in the same RyR subunit. These observations suggest that multiple regions in the RyR2 sequence may contribute to an intra-subunit CaM-binding pocket that undergoes conformational changes during channel gating.

Localization of the dantrolene-binding sequence near the FK506-binding protein-binding site in the three-dimensional structure of the ryanodine receptor

Dantrolene is believed to stabilize interdomain interactions between the NH2-terminal and central regions of ryanodine receptors by binding to the NH2-terminal residues 590-609 in skeletal ryanodine receptor (RyR1) and residues 601-620 in cardiac ryanodine receptor (RyR2). To gain further insight into the structural basis of dantrolene action, we have attempted to localize the dantrolene-binding sequence in RyR1/RyR2 by using GFP as a structural marker and three-dimensional cryo-EM. We inserted GFP into RyR2 after residues Arg-626 and Tyr-846 to generate GFP-RyR2 fusion proteins, RyR2Arg-626-GFP and RyR2Tyr-846-GFP. Insertion of GFP after residue Arg-626 abolished the binding of a bulky GST- or cyan fluorescent protein-tagged FKBP12.6 but not the binding of a smaller, nontagged FKBP12.6, suggesting that residue Arg-626 and the dantrolene-binding sequence are located near the FKBP12.6-binding site. Using cryo-EM, we have mapped the three-dimensional location of Tyr-846-GFP to domain 9, which is also adjacent to the FKBP12.6-binding site. To further map the three-dimensional location of the dantrolene-binding sequence, we generated 10 FRET pairs based on four known three-dimensional locations (FKBP12.6, Ser-437-GFP, Tyr-846-GFP, and Ser-2367-GFP). Based on the FRET efficiencies of these FRET pairs and the corresponding distance relationships, we mapped the three-dimensional location of Arg-626-GFP or -cyan fluorescent protein, hence the dantrolene-binding sequence, to domain 9 near the FKBP12.6-binding site but distant to the central region around residue Ser-2367. An allosteric mechanism by which dantrolene stabilizes interdomain interactions between the NH2-terminal and central regions is proposed.

[The Cologne internet-manual of pain therapy--33 months online, experiences and evaluation]

OBJECTIVE

The improvement of ambulant treatment for patients with chronic headache or cancer pain.

METHODS

Distribution of accepted guidelines and standards by means of the internet in order to make this knowledge known among general practitioners and to give patients better access to this information.

RESULTS

We have built an internet manual about the treatment of chronic headache and cancer pain. About 9100 readers accessed the manual during a period of 33 months. The manual has been completely downloaded 279 times. Physicians and patients very often used search engines to access the manual in their search for information about headache. The terms "migraine" and "tension type headache" were looked up the most.

CONCLUSIONS

It is worthwhile editing medical information for use on the internet and thus making it available to the public.

Calming admins and managers--experiences from four years using thin client technology in a hospital environment

End user desktop computers in a hospital are often full-blown and rich featured PCs. But the distribution of this kind of "computing power" causes big efforts in administration and maintenance and--considering the total cost of owning a PC--is associated with high expenditures of financial and human resources. At the university hospital of Cologne thin client technology is used as an end user desktop device wherever possible. Experiences from four years using this technology are described in this paper.

["Notebook computer" in combination with WWW-technology in multicenter clinical trials and for chronic patient care]

Our purpose was to determine conditions, under which the use of hand-held computers in the diagnosis and therapy of patients with chronic diseases seems to be handy. Two scenarios are presented showing the employment of these computers in a doctor's office and in multicenter clinical trials. Security-related aspects involved in transferring medical data via the internet are discussed.

A high-speed gated baseline restorer and its implementation in a blood cell volume analyser

Accurate measurement of the height of individual pulses in a signal that is a.c.-coupled is dependent upon correcting a changing baseline to a constant value. A new fast baseline restorer, using internally triggered gated feedback with gain, has been designed and a version optimized for Gaussian-shaped pulses. Performance is dependent on the magnitudes of both the forward and the feedback gains. The design presented can achieve a 0.5% accuracy in pulse height for a minimum pulse width of 2.5 microseconds or for 5 microseconds overlapping pulses as long as the overlap is less than 50%. Typical applications for the baseline restorer include blood cell volume measurement systems, scintillation counters and radiation spectroscopy.

Continuous bioluminescent monitoring of cytoplasmic ATP in single isolated rat hepatocytes during metabolic poisoning

We have devised a technique for monitoring cytoplasmic ATP continuously in single hepatocytes. Single isolated rat hepatocytes were injected with the ATP-dependent luminescent protein firefly luciferase, and then superfused with 45 microM luciferin in air-equilibrated medium. Signals of approx. 10-200 photoelectron counts per second could be recorded from individual healthy cells for up to 3 h. The response of the luminescent signal to chemical hypoxia (2-5 mM CN- and 5-10 mM 2-deoxyglucose) was monitored. We found a great cell-to-cell variability in the time course of the ATP decline in response to CN-, 2-deoxyglucose or to their combination; the time for the signal to fall to 10% of the original (corresponding to approx. 100 microM ATP) ranged from approx. 20 to 75 min. This resistance of the cytoplasmic ATP concentration to depletion after blockade of oxidative phosphorylation and glycolysis could be abolished by pretreatment of the cells with etomoxir, which blocks mitochondrial beta-oxidation. Etomoxir alone had no effect on the luciferase signal, but etomoxir-pre-treated cells showed a prompt fall in the luciferase signal starting within 1-2 min of application of cyanide and 2-deoxyglucose and falling to 10% of the original signal in approx. 6-10 min. The technique allows cytoplasmic ATP changes to be monitored in single hepatocytes at concentrations of 1 mM or lower, but more precise calibration of the signal will require correction for the effects of cytoplasmic pH changes.

Mitochondrial ATP-synthase activity in cardiomyocytes after aerobic-anaerobic metabolic transition

It has been hypothesized that, in oxygen-depleted myocardial cells, mitochondria are depolarized and the F1,F0-proton adenosinetriphosphatase (ATPase) catalyzes net ATP hydrolysis when the cells exhibit the signs of an aerobic-anaerobic metabolic transition, which are increased lactate formation and decline in high-energy phosphate reserves [W. Rouslin, C. W. Broge, and I. L. Grupp. Am. J. Physiol. 259 (Heart Circ. Physiol. 28): H1759-H1766, 1990]. This hypothesis was tested by incubating isolated cardiomyocytes from the adult rat in substrate-free Tyrode solution (37 degrees C, pH 7.4) at a PO2 less than or equal to 0.1 Torr, i.e., 1,000-fold below the normal arterial level. At this deep hypoxia, the following results were found. 1) Lactate production was activated to maximal rates and high-energy phosphate contents decreased (aerobic-anaerobic metabolic transition). The inhibitor of the mitochondrial F1,F0-proton ATPase oligomycin, however, added upon establishment of hypoxia, did not slow down, as in the case of depolarized mitochondria, but moderately accelerated energy depletion. 2) Activation of mitochondrial ATP hydrolysis could be provoked in these hypoxic cells by addition of cyanide, antimycin A, and rotenone, i.e., specific inhibitors of certain sites of the respiratory chain. The enhancement of loss of ATP could be inhibited by oligomycin. The results demonstrate that states of deep hypoxia of the cardiomyocyte are possible in which it undergoes an aerobic-anaerobic metabolic transition, indicated by increased lactate formation and progressive loss of cellular energy reserves, and yet mitochondrial ATPase hydrolytic activity is not activated.

Protection of energy status of hypoxic cardiomyocytes by mild acidosis

The question was investigated whether mild acidosis can provide energetic protection on the hypoxic myocardial cell by mechanisms other than negative inotropy. The experimental model used was quiescent ventricular cardiomyocytes isolated from the adult rat. The extracellular pH (pHe) in modified hypoxic Tyrode's solution was varied by changing the concentration of bicarbonate at constant PCO2. The intracellular pH (pHi) was determined with 2',7'-bis-(carboxyethyl)5-(6')-carboxyfluorescein. When the pHe was varied between 6.6 and 7.4, the pHi varied only between 6.91 and 7.14. At pH 7.0, pHi and pHe were identical. Around pHe 7.0, the rate of hypoxic energy loss was lowest. Energetic differences were most prominent after 90 min hypoxia. At this time loss of ATP was 57.1 +/- 2.9% at pHe 6.95 vs. 83.5 +/- 4.1% at pHe 7.4 and 73.9 +/- 2.8% at pHe 6.6; the free energy change of ATP hydrolysis was reduced from 58.8 +/- 0.4 kJ/mol under control conditions to 52.0 +/- 1.1 kJ/mol at pHe 6.95 vs. 45.8 +/- 1.2 and 47.3 +/- 1.4 kJ/mol at pHe 7.4 and 6.6, respectively (means +/- S.D.). Anaerobic lactate production was not significantly altered in the investigated pHe range, indicating that glycolytic energy production remained constant. The results of the present study demonstrate that mild acidosis (pHe around 7.0) has a prominent energy-saving effect on the hypoxic cardiomyocyte due to a reduction in the demand of energy.

Sarcolemmal integrity and metabolic competence of cardiomyocytes under anoxia-reoxygenation

In tissue, mechanical cell-to-cell interactions may contribute to cardiomyocyte injury in anoxia-reoxygenation. In the present study, the disturbance of energy metabolism and cell injury were investigated in isolated cardiomyocytes, free of external mechanical constraints. Cardiomyocytes from adult rat, attached to culture dishes, were exposed to 120 min of anoxia and 15 min of reoxygenation in a substrate-free modified Tyrode solution. The energetic state of the cells in anoxia-reoxygenation was characterized by the free-energy change of ATP hydrolysis (delta GATP), amounting to 57 kJ/mol ATP in normoxia. After 120 min of anoxia, all cells were contracted to 65% of their length and delta GATP decreased to 41 kJ/mol. No lactate dehydrogenase was released. Reoxygenation caused a partial oxygen paradox: immediate hypercontracture of the cells, but no release of lactate dehydrogenase. delta GATP recovered to 51 kJ/mol within 15 min. The results demonstrate that anoxic cardiomyocytes can be energy depleted without losing sarcolemmal integrity. They can undergo hypercontracture, elicited by reoxygenation, and yet an almost normal delta GATP can be reestablished.

The use of the creatine kinase reaction to determine free energy change of ATP hydrolysis in anoxic cardiomyocytes

In isolated cardiomyocytes from adult rat heart the free energy change of ATP hydrolysis (dG) was determined under conditions of substrate-free anoxia. Changes of free cytosolic ADP concentrations, needed for the calculation of dG, were determined by two indirect methods since a direct measurement is not feasible: (i) via the mass action ratio of the creatine kinase reaction (CK) assuming near equilibrium conditions, and (ii) via quantification of the net hydrolysis of ATP to ADP by a detailed balancing of possible contribution to Pi production. Both approaches gave virtually identical results, showing that in anoxia only 6% of the ATP hydrolysed are hydrolysed to ADP and 94% completely to adenosine and further degradation products. The convergence of both methods also indicates that in this model the CK reaction is indeed catalysed near its equilibrium. Therefore estimations of free ADP and dG using its mass action ratio are valid. In anoxic cardiomyocytes dG values fell from 57 kJ/mol in normoxia to 42 kJ/mol after 120 min anoxia, corresponding to a decrease of ATP contents from 24 to 4 nmol/mg protein.