BACKGROUND AND PURPOSE The Ca2+ paradox is an important phenomenon associated with Ca2+ overload‐mediated cellular injury in myocardium. The present study was undertaken to elucidate molecular and cellular mechanisms for the development of the Ca2+ paradox. EXPERIMENTAL APPROACH Fluorescence imaging was performed on fluo‐3 loaded quiescent mouse ventricular myocytes using confocal laser scanning microscope. KEY RESULTS The Ca2+ paradox was readily evoked by restoration of the extracellular Ca2+ following 10–20 min of nominally Ca2+‐free superfusion. The Ca2+ paradox was significantly reduced by blockers of transient receptor potential canonical (TRPC) channels (2‐aminoethoxydiphenyl borate, Gd3+, La3+) and anti‐TRPC1 antibody. The sarcoplasmic reticulum (SR) Ca2+ content, assessed by caffeine application, gradually declined during Ca2+‐free superfusion, which was further accelerated by metabolic inhibition. Block of SR Ca2+ leak by tetracaine prevented Ca2+ paradox. The Na+/Ca2+ exchange (NCX) blocker KB‐R7943 significantly inhibited Ca2+ paradox when applied throughout superfusion period, but had little effect when added for a period of 3 min before and during Ca2+ restoration. The SR Ca2+ content was better preserved during Ca2+ depletion by KB‐R7943. Immunocytochemistry confirmed the expression of TRPC1, in addition to TRPC3 and TRPC4, in mouse ventricular myocytes. CONCLUSIONS AND IMPLICATIONS These results provide evidence that (i) the Ca2+ paradox is primarily mediated by Ca2+ entry through TRPC (probably TRPC1) channels that are presumably activated by SR Ca2+ depletion; and (ii) reverse mode NCX contributes little to the Ca2+ paradox, whereas inhibition of NCX during Ca2+ depletion improves SR Ca2+ loading, and is associated with reduced incidence of Ca2+ paradox in mouse ventricular myocytes.

We applied a dialysis technique to the hearts of anesthetized cats and examined whether the concentration of dialysate norepinephrine (NE) reflected NE disposition at the cardiac sympathetic nerve terminals. Dialysis probes were implanted in the left ventricular wall, and dialysate NE concentrations were measured as an index of myocardial interstitial NE levels. Stimulation of stellate ganglia significantly increased dialysate NE responses that were suppressed by local administration of an NE-releasing inhibitor (omega-conotoxin GVIA, 10 microM). Increments in basal dialysate NE levels were correlated with concentrations of a locally administered neuronal uptake blocker (desipramine; 1, 10, and 100 microM). Desipramine (100 microM) augmented stimulation-induced dialysate NE responses. Local administration of a neuronal vesicle uptake blocker (reserpine, 1 and 10 microM) did not alter dialysate NE levels but increased dialysate dihydroxyphenylglycol levels. An NE-releasing amine (tyramine, 100 microg/ml) was locally administered to examine NE storage capacity at the nerve terminal. The tyramine-induced NE-releasing response was completely abolished by pretreatment with reserpine (1 mg/kg i.p.). Thus cardiac dialysis with local administration of a pharmacological tool offers a new, concise approach to assessment of neuronal NE release, uptake, vesicle uptake, and storage capacity by cardiac sympathetic nerve terminals.

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Intraoperative pulmonary fat and bone-marrow embolism is a serious complication of bone and joint surgery. We have investigated the occurrence and incidence of intraoperative embolism in patients undergoing elective lumbar spinal surgery with or without instrumentation. Sixty adult patients with lumbar degenerative disease were examined by intraoperative transoesophageal echocardiography while undergoing posterior lumbar surgery. Of these, 40 underwent surgery with instrumentation and 20 without. Moderate to severe (grade 2 or 3 according to the grading scale of Pitto et al) embolic events were seen in 80% of the instrumented patients but in none of the non-instrumented patients (p < 0.001). The insertion of pedicle screws was particularly associated with large numbers of pulmonary emboli, while the surgical approach, laminectomy, disc removal and bone harvesting were associated with small numbers of emboli. We consider that, as in arthroplasty and intramedullary fixation of fractures, these embolic events are relevant to the development of potentially fatal fat embolism during spinal surgery.

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