No abstract

No abstract

We have exmined the effect of a synthetic analogue of human et-atrial natriuretic peptide (ANP), APH, on renin release in cultured renal juxtaglomerular cells (JGA cells). Using cell cultures containing 80-90% renal juxtaglomerular cells, we found that ANP (10-13-10-9 M) strongly inhibited renin release from the cells in a dose-dependent fashion (ki, 10 pM) to about 10% of control. Inhibition of renin release by ANP was paralleled by an increase in cellular cGMP levels; while in the presence of the cGMP-phosphodiesterase inhibitor M&B 22948 (1 mM), concentrations of ANP lower by a factor of 100 were required to obtain the same effects on renin release and cGMP levels. The guanylate cyclase inhibitor methylene blue (10 IAM), on the other hand, shifted the dose-response curves for renin release and cGMP levels to 100-fold higher concentrations of ANP. Neither the influx of 45Ca into the cells nor the intracellular quin-2 signal, which is a measure for changes of intracellular Ca concentration, was in any way altered by ANP. Our results suggest that ANP inhibits renin release from juxtaglomerular cells by a cGMP-dependent process that does not involve changes in intracellular calcium.Two major effects of atrial natriuretic peptide (ANP) on renal function have been described, namely the enhancement of sodium and water excretion (cf. refs. 1 and 2) and the suppression of renin release (3)(4)(5). Inhibition of renin release by ANP leading to a diminished formation of angiotensin II (AI) would result in decreased vascular tone and impaired aldosterone secretion. Both effects are of physiological importance during states of expanded extracellular volume, in which enhanced release of ANP from the atrium is observed (6, 7).The mechanism by which ANP inhibits renal renin release is as yet a matter of debate (2). In view of the increased filtration rate of NaCl caused by the ANP, which leads to an increased NaCl load at the macula densa, it has been speculated that ANP inhibits renin release fromjuxtaglomerular cells via the macula densa receptor (3, 4). However, a direct effect of ANP on juxtaglomerular cells could not be excluded on the basis of experimental evidence. Therefore, we wanted to investigate whether or not ANP directly inhibits renin release by renal juxtaglomerular cells.We have developed a cell culture system that contains around 50% juxtaglomerular cells (8, 9). We now have improved this method by including a Percoll-density gradient in the cell preparation procedure. As a result, cell cultures can be obtained that contain regularly between 80 and 90% juxtaglomerular cells.We found that ANP strongly inhibits renin release from these cultured cells and, furthermore, obtained strong evidence that the inhibitory effect of ANP is mediated by cGMP and does not involve an increase in intracellular calcium. MATERIALS AND METHODSCell Culture. Isolation ofjuxtaglomerular cells was essentially as described (8,9). In brief, rat kidneys were perfused in situ with citrate buffer. After exstirpation of the kidne...

Cell contacts between elements of the tunica media and the intima in the afferent and efferent glomerular arteriole and in the interlobular artery were studied and evaluated semiquantitatively in thin sections of rat and mouse kidney. In the afferent arterioles, including their juxtaglomerular portion, contacts were seen between endothelial and smooth muscle cells, and between endothelial and granulated (renin producing) cells. The form of these musculo-endothelial contacts varied from simple appositions of perikarya and cell processes to extensive club-shaped indentations of endothelial cells into media cells (common) or media cells into endothelial cells (rare). Most of these cell contacts seem to contain myoendothelial gap junctions. Fewer, mostly club-shaped myoendothelial contacts were found in the interlobular arteries of rats and mice than in their afferent arterioles. Simple membrane appositions predominated among the numerous myoendothelial contacts of efferent arterioles. Similar results (without quantitative analysis) were obtained in the kidney of Tupaia belangeri. The myoendothelial contacts may allow the detection and propagation of mechanical (autoregulatory) and humoral stimuli.

The juxtaglomerular apparatus (JGA) in the rabbit kidney was examined by transmission electron microscopy and by freeze fracturing. It was found, that the Goormaghtigh cells of the JGA are extensively coupled with the mesangial cells within the glomerular tuft by gap junctions. A broad band of gap junctions starting within the Goormaghtigh cells, traversing the transitional area at the root of the glomerular tuft and continuing along the mesangial cells has been revealed by freeze fracturing. No gap junctional connections to the macula densa cells have been found. In accordance with data from literature it may be stated that all smooth muscle derived cell groups at the vascular pole of the glomerulus (smooth muscle cells of the vas afferens and efferens, granular cells, Goormaghtigh cells, mesangial cells) are extensively coupled by gap junctions with each other. It is supposed that this cell system may act as a synchronized functional unit.