Abstract-Hydroxyl radicals (OH) are involved in the development of reperfusion injury and myocardial failure. In the acute phase of the OH-mediated diastolic dysfunction, increased intracellular Ca 2ϩ levels and alterations of myofilaments may play a role, but the relative contribution of these systems to myocardial dysfunction is unknown. Intact contracting cardiac trabeculae from rabbits were exposed to OH, resulting in an increase in diastolic force (F dia ) by 540%. Skinned fiber experiments revealed that OH-exposed preparations were sensitized for Ca 2ϩ (EC 50 : 3.27Ϯ0.24ϫ10Ϫ6 versus 2.69Ϯ0.15ϫ10 Ϫ6 mol/L; PϽ0.05), whereas maximal force development was unaltered. Western blots showed a proteolytic degradation of troponin T (TnT) with intact troponin I (TnI). Blocking of calpain I by MDL-28.170 inhibited both TnT-proteolysis and Ca 2ϩ sensitization, but failed to prevent the acute diastolic dysfunction in the intact preparation. The OH-induced diastolic dysfunction was similar in preparations with intact (540Ϯ93%) and pharmacologically blocked sarcoplasmic reticulum (539Ϯ77%), and was also similar in presence of the L-type Ca 2ϩ -channel antagonist verapamil. In sharp contrast, inhibition of the reverse-mode sodium-calcium exchange by KB-R7943 preserved diastolic function completely. Additional experiments were performed in rat myocardium; the rise in diastolic force was comparable to rabbit myocardium, but Ca 2ϩ sensitivity was unchanged and maximal force development was reduced. This was associated with a degradation of TnI, but not TnT. Electron microscopic analysis revealed that OH did not cause irreversible membrane damage. We conclude that OH-induced acute diastolic dysfunction is caused by Ca 2ϩ influx via reverse mode of the sodium-calcium exchanger. Degradation of troponins appears to be species-dependent but does not contribute to the acute diastolic dysfunction.

Auto-antibodies against purified human calreticulin were determined by an ELISA in sera from patients with systemic lupus erythematosus (SLE) and from healthy persons or patients without an autoimmune disease. More than 80% of patients with SLE had titers exceeding the highest value obtained in the group without SLE. Almost 30% of the patients had also elevated auto-antibody titers against purified rat grp94, another resident ER-protein of the KDEL-protein family, but not against rat ERp72 (CaBP2), an ER-resident protein of the proteindisulfide isomerase family. It could, however, be excluded that calreticulin is the Ro/SS-A antigen on the basis of the following observations: 1) Calreticulin purified from rat, bovine or human liver contained far less than 1 mol of phosphate per mol of calreticulin, showed an E280/E260-absorption ratio of about 2.0, and did not contain extractable RNA; 2) Sera from patients with SLE did not react with or precipitate endogenous calreticulin from Hep G2 cells; they did, however, precipitate hY-RNA from these cells; 3) Sera from SLE-patients, but not anti-calreticulin antisera precipitated [32P]-hY-RNA from [32P]-labelled Hep G2 cells.

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We investigated the hypothesis that increased intracellular [Na + ] i in heart failure contributes to preservation of SR Ca 2+ load which may become particularly evident at slow heart rates.[Na + ] i in SBFI-loaded myocytes from rabbits with pacing-induced heart failure (PHF) was significantly higher at each frequency as compared to Sham-operated animals. Furthermore, PHF rabbits demonstrated reduced SR Ca 2+ -ATPase protein levels (À 37%, p < 0.04) but unchanged Na + /Ca 2+ exchanger protein levels. At 0.25 Hz, isometric force was similar in cardiac trabeculae from PHF rabbits as compared to control (PHF, 3.6 T 1.3; Sham, 4.4 T 0.6 mN/mm 2 ). Rapid cooling contractures (RCCs) were unchanged indicating preserved SR Ca 2+ load at this frequency. In Sham, isometric twitch force increased with rising frequencies to 29.0 T 2.8 mN/mm 2 at 3.0Hz ( p < 0.05) as compared to 0.25 Hz. RCCs showed a parallel increase by 186 T 47% ( p < 0.01). In PHF, frequency-dependent increase in force (15.8 T 4.7 mN/mm 2 at 3.0 Hz) and RCCs (increase by 70 T 40%) were significantly blunted.Thus, in PHF in rabbits SR Ca 2+ load is preserved at low frequencies despite decreased SR Ca 2+ -ATPase expression. This may result from [Na + ] i -dependent changes in Na + /Ca 2+ exchanger activity.