The amyloid precursor protein (APP) is proteolytically processed by ␤-and ␥-secretases to release amyloid ␤, the main component in senile plaques found in the brains of patients with Alzheimer disease. Alternatively, APP can be cleaved within the amyloid ␤ domain by ␣-secretase releasing the non-amyloidogenic product sAPP␣, which has been shown to have neuroprotective properties. Several G protein-coupled receptors are known to activate ␣-secretase-dependent processing of APP; however, the role of G protein-coupled nucleotide receptors in APP processing has not been investigated. Here it is demonstrated that activation of the G proteincoupled P2Y 2 receptor (P2Y 2 R) subtype expressed in human 1321N1 astrocytoma cells enhanced the release of sAPP␣ in a time-and dose-dependent manner. P2Y 2 Rmediated sAPP␣ release was dependent on extracellular calcium but was not affected by 1,2-bis(2-aminophenoxy)ethane-N,N,N,-trimethylammonium salt, an intracellular calcium chelator, indicating that P2Y 2 R-stimulated intracellular calcium mobilization was not involved. Inhibition of protein kinase C (PKC) with GF109203 or by PKC down-regulation with phorbol ester pre-treatment had no effect on UTP-stimulated sAPP␣ release, indicating a PKC-independent mechanism. U0126, an inhibitor of the mitogen-activated protein kinase pathway, partially inhibited sAPP␣ release by UTP, whereas inhibitors of Src-dependent epidermal growth factor receptor transactivation by P2Y 2 Rs had no effect. The metalloprotease inhibitors phenanthroline and TAPI-2 and the furin inhibitor decanoyl-ArgVal-Lys-Arg-chloromethylketone also diminished UTPinduced sAPP␣ release. Furthermore, small interfering RNA silencing of an endogenous adamalysin, ADAM10 or ADAM17/TACE, partially suppressed P2Y 2 R-activated sAPP␣ release, whereas treatment of cells with both ADAM10 and ADAM17/TACE small interfering RNAs completely abolished UTP-activated sAPP␣ release. These results may contribute to an understanding of the non-amyloidogenic processing of APP.P2 nucleotide receptors modulate a wide range of physiological responses following their activation by extracellular nucleotides (1, 2). The G protein-coupled P2Y 2 receptor (P2Y 2 R) 1 subtype is fully activated by equivalent concentrations of ATP or UTP (3-5) and is up-regulated in salivary gland models of stress and disease (6 -8) as well as in blood vessels after balloon angioplasty and in collared carotid arteries, where it induces intimal hyperplasia and inflammation by increasing smooth muscle cell proliferation and leukocyte infiltration (9, 10). Moreover, nucleotides are released from damaged cells of all tissues and from excited neurons, aggregating platelets, and contracting smooth muscle under physiological conditions (2, 11).The diversity of cellular responses mediated by P2Y 2 Rs is due in part to unique structural features that enable these receptors to stimulate a variety of signal transduction pathways. In addition to the classical stimulation of G␣ q -dependent phospholipase C (12, 13), the P2Y 2 R c...

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Ligation of the main excretory duct of the rat submandibular gland (SMG) produces a pronounced atrophy that is reversed upon ligature removal. Based on previous studies by our group and others suggesting that P2Y(2) nucleotide receptors are upregulated in response to tissue damage, we hypothesized that P2Y(2) receptor activity and mRNA levels would increase after duct ligation and return to control levels after ligature removal. Our results support this hypothesis. Intracellular Ca(2+) mobilization in response to the P2Y(2) receptor agonist UTP in SMG cells was increased significantly after ligation periods of 1.5 to 7 days, whereas no significant response was observed in the contralateral, nonligated gland. P2Y(2) receptor mRNA, as measured by semiquantitative RT-PCR, increased about 15-fold after 3 days of ligation. These increases reverted to control levels by 14 days after ligature removal. In situ hybridization revealed that the changes in P2Y(2) receptor mRNA abundance occurred mostly in acinar cells, which also were more adversely affected by ligation, including an increase in the appearance of apoptotic bodies. These findings support the idea that P2Y(2) receptor upregulation may be an important component of the response to injury in SMG and that recovery of normal physiological function may signal a decreased requirement for P2Y(2) receptors.

The protonephridia of Protodrilus rubropharyngeus are described. They consist of a terminal cell, one nephridiopore cell, and different types of duct cells (proximal, medial, distal) with the duct running intracellularly. Reabsorption takes place in the duct by means of very unique lamellar foldings. An interesting characteristic of the nephridial system in P. rubropharyngeus is the presumed double filtration of the primary urine that occurs in the walls of both the lateral blood lacunae and the terminal cell. The structure of excretory organs in relation to the particular coelomatic conditions found in different groups of polychaetes is discussed.9 Biologische Anstalt Helgoland, Hamburg