Skinned fibres from bovine ventricles exhibited spontaneous tension oscillations when MgADP and inorganic phosphate (Pi) were added to the solution bathing fibres in the relaxed state (ADP-SPOC). A similar type of oscillation was observed at intermediate concentrations of free Ca2+ in the absence of MgADP and Pi (Ca-SPOC). To investigate the correlation between ADP-SPOC and Ca-SPOC, we constructed two-dimensional state diagrams of cardiac muscle using different concentrations of Pi (0-20 mM) and free Ca2+ [pCa=around 5 (+Ca2+), pCa=5.15-6.9 and +EGTA (-Ca2+)], with varying concentrations of MgADP (0-10 mM), with 2 mM MgATP and 2 mM free Mg2+ maintaining ionic strength at 0.15+/-0.01 M, pH 7.0, 25 degrees C. The three-dimensional (pCa-Pi-MgADP) state diagram thus obtained was divided into three regions, i.e. the contraction region in which tension oscillation was undetectable, the spontaneous tension oscillation (SPOC) region and the relaxation region. We found that the regions of ADP-SPOC and Ca-SPOC were continuously connected by a single oscillation region sandwiched between the contraction and relaxation regions. The state diagram, which encompasses physiological conditions, shows that the probability of SPOC is higher in cardiac muscle than in skeletal muscle. From these results, we suggest that, despite distinct ionic conditions, the molecular state of cross-bridges during SPOC is common to both ADP-SPOC and Ca-SPOC.

Adenosine Diphosphate↗

PubMedDate not supplied

Modification of apoptosis-inducing activity of gallic acid by saliva.

Gallic acid, a structural unit of tannin, induced apoptotic cell death, characterized by nuclear condensation and caspase activation in human oral tumor cell lines (HSC-2, HSG). Agarose gel electrophoresis demonstrated that gallic acid produced large DNA fragments in these cells, as well as in T-cell leukemia (MOLT-4) and erythroleukemia (K-562) cells, whereas it induced internucleosomal DNA fragmentation in human myelogenous leukemic cell lines (HL-60, ML-1, U-937, THP-1). This indicates that induction of internucleosomal DNA fragmentation or production of large DNA fragments depends on both target cells and inducers. Addition of total saliva dose-dependently reduced the cytotoxicity induction by gallic acid. These data suggested that the biological action of gallic acid might be modified by physiological fluids.

Antioxidants↗