PubMed · 8631433
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G J Chiche. 1995. Double-string technique for final impressions--practical applications.. https://pubmed.ncbi.nlm.nih.gov/8631433/
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Biocompatibility of mineral trioxide aggregate and ethoxybenzoic acid cement was investigated by subcutaneous and intraosseous implantation of the materials in rats. Tissue reactions were studied at 15, 30, and 60 days after implantation. Subcutaneous implantation of mineral trioxide aggregate initially elicited severe reactions with coagulation necrosis and dystrophic calcification; the reactions, however, subsided to mostly moderate with time. Subcutaneous implantation of ethoxybenzoic acid cement initially elicited mostly moderate reactions that subsided to mild in time. Osteogenesis was not observed with either material upon subcutaneous implantation indicating that neither material is osteoinductive. Reactions to intraosseous implants of both materials were less intense than with subcutaneous implantation. Osteogenesis occurred in association with intraosseous implants indicating that both materials are osteoconductive.
To investigate how G protein alpha subunit localization is regulated under basal and activated conditions, we inserted green fluorescent protein (GFP) into an internal loop of Galpha(q). alpha(q)-GFP stimulates phospholipase C in response to activated receptors and inhibits betagamma-dependent activation of basal G protein-gated inwardly rectifying K(+) currents as effectively as alpha(q) does. Association of alpha(q)-GFP with the plasma membrane is reduced by mutational activation and eliminated by mutation of the alpha(q) palmitoylation sites, suggesting that alpha(q) must be in the inactive, palmitoylated state to be targeted to this location. We tested the effects of activation by receptors and by AlF(4)(-) on the localization of alpha(q)-GFP in cells expressing both alpha(q)-GFP and a protein kinase Cgamma-red fluorescent protein fusion that translocates to the plasma membrane in response to activation of G(q). In cells that clearly exhibit protein kinase Cgamma-red fluorescent protein translocation responses, relocalization of alpha(q)-GFP is not observed. Thus, under conditions associated with palmitate turnover and betagamma dissociation, alpha(q)-GFP remains associated with the plasma membrane. These results suggest that upon reaching the plasma membrane alpha(q) receives an anchoring signal in addition to palmitoylation and association with betagamma, or that during activation, one or both of these factors continues to retain alpha(q) in this location.
Small G proteins of the Rab family are regulators of intracellular vesicle traffic. Their intrinsic rate of GTP hydrolysis is very low but is enhanced by specific GTPase-activating proteins (GAPs) that switch G proteins to their inactive form. We have characterized the activity of recombinant Rab3-GAP on Rab3A in solution. The K(m) and K(d) values (75 microm) indicate a low affinity of Rab3-GAP for its substrate. The affinity is higher for the transition state analog Rab3A:GDP:AlF(x) (15 microm). The k(cat) (1 s(-)(1)) is within the range of values reported for other GAPs. A mutation in the switch I region of Rab3A disrupted the interaction with Rab3-GAP. Furthermore, Rabphilin, a putative target of Rab3, inhibited the activity of Rab3-GAP on Rab3. Therefore, the Rab3-GAP-binding site involves the switch I region of Rab3 and overlaps with the Rabphilin-binding domain. Substitution of a single arginine residue (Arg-728) of Rab3-GAP disrupted its catalytic activity but not its interaction with Rab3A. We propose that Rab3-GAP, like Ras- and Rho-GAPs, stabilizes the transition state of Rab3 and provides a critical arginine residue to accelerate the GTPase reaction.