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ATP released from damaged cells or by controlled secretion could be an important factor in the formation or remodeling of bone. In a variety of other tissues ATP has been shown to control cellular processes by acting on P2-purinoceptors and activating the calcium signaling pathway. Here we demonstrate for the first time that extracellular ATP increases the intracellular free calcium [Ca2+]i concentration in normal human osteoblasts and in SaOS-2 cells, a human osteosarcoma-derived cell line, but not in ROS 17/2.8 cells. The ATP-induced increase in [Ca2+]i was dose dependent, and the concentrations of ATP required were similar to those reported to regulate cellular functions in other cell types. Although ATP is metabolized rapidly by bone cells, the effects on [Ca2+]i appeared to be mediated directly by ATP rather than one of its metabolites. Adenosine 3-thiotriphosphate, a nonhydrolyzable analog of ATP, induced similar changes in [Ca2+]i. This indicates that P2-purinoceptors are present on osteoblast-like cells and that extracellular ATP from various sources might be an important factor in the regulation of osteoblast functions.

Summary A prospective study of 128 adult cardiac surgical patients was undertaken in order to quantify net magnesium loss and its relationship to serum magnesium levels and postoperative problems, particularly arrhythmias. Peri-operative magnesium flux on the first day was calculated from the administered magnesium (in cardioplegia solution and intravenous infusion) and urinary magnesium loss. Magnesium input ranged from 24 mmol to 40 mmol, resulting in a net magnesium gain in 94% of patients. Hypomagnesaemia, identified in 34% of patients pre-operatively and 30% of patients postoperatively, had no significant correlation with the measured peri-operative magnesium flux or the electrocardiograph corrected-QT interval. Fifty-three patients developed postoperative arrhythmias, but there was no significant correlation with the serum total magnesium concentration, or with the peri-operative change in serum magnesium level, magnesium flux, or QT interval. The data suggest that serum total magnesium is not a useful measurement upon which to base preventive or therapeutic measures in cardiac surgical patients.

Fast muscles of the rat hind limb were stimulated continuously at 10 or 20 Hz for periods of 55–61 days by means of an implantable neuromuscular stimulator. Gel electrophoresis clearly demonstrated the presence in stimulated muscles of slow myosin light and heavy chains, although fast isoforms were still present in all cases. Thus, contrary to previous reports, induction of slow myosin isoforms does occur in this, as in other, mammalian species. The time course of the response to stimulation appears to be more extended than that seen in the rabbit.