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PubMedDate not supplied

The effects of cadmium on a clonal osteogenetic cell, MC3T3-E1: inhibition of calcification and induction of metallothionein-like protein by cadmium.

To clarify the effects of cadmium (Cd) on bone formation, a clonal osteogenetic cell, MC3T3-E1, was used in the present study. After 24 h of culture, Cd at 1 ppm and above decreased DNA synthesis and alkaline phosphatase activity, but Cd at 1.5 ppm caused no significant decrease in collagen content. The cells treated with Cd (0.03-1.0 ppm) for 24 h showed the dose-dependent effects on metallothionein-like protein synthesis. The marked increase of Cd content unbound to metallothionein (MT)-like protein with cadmium at 1 ppm may be responsible for the toxic effects of cadmium. After 10 days of culture, the accumulation of 45Ca to the cell layer decreased with increasing level of cadmium at 0.03 and 0.1 ppm. The cadmium-treated cell layer showed a weaker reaction to histochemical staining for mineral compared with control culture. This result suggests that Cd inhibits an initial process of calcification.

Alkaline Phosphatase↗

PubMedDate not supplied

Propylbenzilylcholine mustard discriminates between two subtypes of muscarinic cholinoceptors in guinea-pig taenia caecum.

A 10-min treatment of isolated guinea-pig taenia caecum with propylbenzilylcholine mustard (PrBCM; 3 x 10(-7) M) inhibited concentration-response curves of 5 full agonists used. A 50-min treatment with PrBCM produced a further inhibition of their curves. However, a 90-min treatment with PrBCM had no further significant inhibitory effect on their curves. Concentration-response curves of 5 partial agonists were completely inhibited by the 50-min treatment with PrBCM (3 x 10(-7) M). The limiting effect of PrBCM observed on the concentration-response curves of the full agonists was not found on the curves of the partial agonists. These results suggest that there are 2 subtypes of muscarinic cholinoceptors, PrBCM-sensitive and -resistant muscarinic receptors, which are discriminated by PrBCM but not by atropine, pirenzepine or AF-DX 116. The pKA value (a negative logarithm of dissociation constant) of carbachol to PrBCM-sensitive receptors is smaller than that to PrBCM-resistant ones, suggesting that the full agonists may be more sensitive to PrBCM-resistant receptors than to PrBCM-sensitive ones. The partial agonists produced contractions of the taenia caecum predominantly through an activation of PrBCM-sensitive receptors, while the full agonists contracted the taenia caecum through the interaction of two subtypes. The responses to nicotine and to electrical stimulation were inhibited by the 50-min treatment with PrBCM, suggesting that PrBCM-sensitive receptors might play a physiological role.

Animals↗