No abstract

No abstract

No abstract

No abstract

The 70-kilodalton family of heat shock proteins (Hsp 70) has been implicated in posttranslational protein assembly and translocation. Binding of cytosolic forms of Hsp 70 (Hsp 72,73) with nascent proteins in the normal cell was investigated and found to be transient and adenosine triphosphate (ATP)-dependent. Interaction of Hsp 72,73 with newly synthesized proteins appeared to occur cotranslationally, because nascent polypeptides released prematurely from polysomes in vivo can be isolated in a complex with Hsp 72,73. Moreover, isolation of polysomes from short-term [35S]Met-labeled cells (pulsed) revealed that Hsp 72,73 associated with nascent polypeptide chains. In cells experiencing stress, newly synthesized proteins coimmunoprecipitated with Hsp 72,73; however, in contrast to normal cells, interaction with Hsp 72,73 was not transient. A model consistent with these data suggests that under normal growth conditions, cytosolic Hsp 72,73 interact transiently with nascent polypeptides to facilitate proper folding, and that metabolic stress interferes with these events.

Abstract-Superoxide radical (O 2Ϫ ) is increased in the vessel wall of spontaneously hypertensive rats (SHR) where its blockade potentiates endothelium-dependent vasodilation. The purpose of this study was to determine the role of O 2 Ϫ in the hypertension and renal vasoconstriction of SHR and its interaction with nitric oxide (NO). Baseline mean arterial pressure (MAP) and renal vascular resistance were markedly elevated in SHR (nϭ6)

Tubular-fluid reabsorption by specialized cells of the nephron at the junction of the ascending limb of the loop of Henle and the distal convoluted tubule, termed the macula densa, releases compounds causing vasoconstriction of the adjacent afferent arteriole. Activation of this tubuloglomerular feedback response reduces glomerular capillary pressure of the nephron and, hence, the glomerular filtration rate. The tubuloglomerular feedback response functions in a negative-feedback mode to relate glomerular capillary pressure to tubular-fluid delivery and reabsorption. This system has been implicated in renal autoregulation, renin release, and longterm body fluid and blood-pressure homeostasis. Here we report that arginine-derived nitric oxide, generated in the macula densa, is an additional intercellular signaln molecule that is released during tubular-fluid reabsorption and counters the vasoconstriction of the afferent arteriole. Antibody to rat cerebellar constitutive nitric oxide synthase stained rat macula densa cells specifically. Microperfusion of the macula densa segment of single nephrons with N'-methyl-L-arginlne (an inhibitor of nitric oxide synthase) or with pyocyanin (a lipidsoluble inhibitor of endothelium-derived relaxation factor) showed that generation of nitric oxide can vasodilate the afferent arteriole and increase glomerular capillary pressure; this effect was blocked by drugs that prevent tubular-fluid reabsorption. We conclude that nitric oxide synthase in macula densa cells is activated by tubular-fluid reabsorption and mediates a vasodilating component to the tubuloglomerular feedback response. These finding imply a role for argininederived nitric oxide in body fluid-volume and blood-pressure homeostasis, in addition to its established roles in modulation of vascular tone by the endothelium and in neurotransmission.Goormaghtigh (1) suggested that the macula densa is the sensor for a stimulus from tubular fluid that is conveyed to the glomerulus. Subsequently, Thurau and Schnermann (2) identified that the stimulus was the delivery and reabsorption of NaCl by this segment. This tubuloglomerular feedback response functions as a negative-feedback control mechanism, whereby glomerular filtration of NaCI, with delivery to and reabsorption by the macula densa, induces release of mediator(s) that cause afferent-arteriolar vasoconstriction and a reduction in glomerular capillary pressure and glomerular filtration rate (2). Although the signaling mechanisms or molecules inducing afferent-arteriolar vasoconstriction have not been clearly defined, the response is promoted by adenosine acting on adenosine type 1 receptors (3), angiotensin II (4), and thromboxane A2 (5)-Previous studies have established that L-arginine-derived nitric oxide (NO) is produced by several cells within the kidney, including isolated glomerular mesangial (6) and endothelial cells (7), and a renal epithelial cell line (8), but its integrative role in the control ofrenal function is not yet clear (9). In the vessel wall, ...

The molecular chaperone proteins, particularly Hsp60 and Hsp70, have been implicated in essential cell functions under both normal and stress conditions (reviewed in refs 1-5). Members of the family of heat-shock proteins of M(r) 70K, Hsp70, bind to unfolded proteins and short peptides. Addition of Mg-ATP results in the dissociation of the substrate polypeptides from the chaperone, but as ATP-gamma S (an ATP analogue that is only slowly hydrolysable) cannot substitute for ATP in this reaction, it has been concluded that ATP hydrolysis is necessary to dissociate Hsp70-substrate protein complexes. By independently measuring the rates of ATP hydrolysis and substrate protein dissociation, we show here that Mg-ATP binding but not Mg-ATP hydrolysis is essential for substrate dissociation. We also show that there is an absolute requirement for K+ for the effect of Mg-ATP: only the combination of K+ and Mg-ATP will cause the conformational change in Hsp70 that is necessary for substrate dissociation. Moreover, in the absence of K+, Mg-ATP favours complex formation. We consider these results in terms of a G-protein-like model.