Effects of osmolality and oxygen availability on soluble cyclic AMP-dependent protein kinase activity of rat renal inner medulla.

Abstract

A B S T R A C T The renal inner medulla is ordinarily exposed to osmolalities that are much higher and to 02 tensions that are lower than those in other tissues. The effects of media osmolality and 02 availability on basal and arginine vasopressin(AVP)-responsive soluble cyclic (c)AMP-dependent protein kinase activity were examined in slices ofrat inner medulla. Increasing total media osmolality from 305 to 750 or 1,650 mosM by addition of urea plus NaCl to standard Krebs-Ringer bicarbonate buffer significantly reduced basal cAMP content and protein kinase activity ratios. This occurred in the presence or absence of 02. Incubation of slices in high osmolality buffer also blunted increases in inner medullary slice cAMP and protein kinase activity ratios induced by 02. These changes reflected predominantly an action of the urea rather than the NaCl content of high osmolality buffers. In contrast to effects on basal activity, high media osmolality significantly enhanced activation of inner medullary protein kinase by AVP. Conversely, increases in media 02 content suppressed AVP stimulation of enzyme activity. This inhibitory effect of 02 was best expressed at low osmolality. Naproxen and ibuprofen, inhibitors of prostaglandin biosynthesis, reduced basal kinase activity ratios and increased AVP responsiveness in the presence, but not in the absence, of 02. Exogenous prostaglandins (PG) modestly increased (PGE2 and PGE,) or did not change (PGFw) INTRODUCTIONUnder physiologic conditions the inner medulla of the kidney is routinely exposed to osmolalities that are much higher and to oxygen tensions that are much lower than those that normally pertain in other mammalian tissues (1-3). The potentially important influence of these unique conditions has not always been considered in studies of inner medullary metabolism. Recent observations suggest that both oxygen availability and solute concentration significantly alter inner medullary cyclic (c)AMP1 economy (4-6). These same factors may also be determinants of the expression of the cellular actions of cAMP in inner medulla. Current evidence indicates that the biologic actions of cAMP in mammalian cells are transmitted through phosphorylation reactions mediated by cAMP-dependent protein kinases (7). cAMP-responsive kinase activity is present in both the soluble and particulate fractions of kidney (8,9) and other tissues (10, 11), but the properties and regulation of the soluble enzyme activity have been most extensively examined (12)(13)(14)(15) (16,17) and medulla (18). However, regulation of renal medullary protein kinase as a function of solute concentration and tissue oxygenation has not been examined. Accordingly, in the present study, we assessed the effects of media osmolality and 02 availability on basal and arginine vasopressin (AVP)-responsive soluble cAMP-dependent protein kinase activity in slices of rat inner medulla. METHODSPreparation of tissue. Male Sprague-Dawley rats (ZivicMiller Laboratories, Inc., Pittsburgh, Pa.) weighing 300-350 g were faste...

Calcium-dependent action of osmolality on adenosine 3',5'-monophosphate accumulation in rat renal inner medulla: evidence for a relationship to calcium-responsive arachidonate release and prostaglandin synthesis.

“…Previous studies of rat inner medulla have indicated that solute concentration may be an important determinant of basal and arginine vasopressin (AVP)'-responsive cyclic AMP (cAMP) accumulation (1). Thus, as media osmolality is increased, basal cAMP content of inner medullary slices declines markedly, whereas AVP-responsive cAMP is either unchanged or enhanced (1).…”

“…Previous studies of rat inner medulla have indicated that solute concentration may be an important determinant of basal and arginine vasopressin (AVP)'-responsive cyclic AMP (cAMP) accumulation (1). Thus, as media osmolality is increased, basal cAMP content of inner medullary slices declines markedly, whereas AVP-responsive cAMP is either unchanged or enhanced (1). Consistent with the effects on tissue cAMP content, the basal activity of soluble cAMP-dependent protein kinase also falls in inner medulla, and AVP-responsive enzyme activity is concurrently enhanced at higher osmolalities (1,2).…”

<b>EFFECTS OF OSMOLALITY ON THE INTERACTION BETWEEN VASOPRESSIN AND PROSTAGLANDINS IN RAT RENAL PAPILLARY COLLECTING TUBULE CELLS IN </b><b>CULTURE </b>

“…(I0), but did not use other osmotic solutions. Increase in cAMP production by hypertonicity was observed in a similar preparation of rats in the absence of the phosphodiesterase inhibitor (30), in the isolated papillary collecting tubule (10), and in the kidney slices (6). Edwards et al (10) have demonstrated that in the isolated papillary collecting tubule both adenylate cyclase and phosphodiesterase activities are inhibited by hyperosmolality of 1,400-2,000 mOsm/kg H20, and also that cAMP increased significantly with an increase in osmolality from 300 to 2,000 mOsm/kg H20.…”

Renal inner medullary prostaglandin synthesis. A calcium-calmodulin-dependent process suppressed by urea.

“…This has also been observed in the particulate fraction of guinea pig brain (33). Even in brain however, the extent of CaM-like activity depletion achieved was greater than in IM (33 (1,6,(38)(39)(40)(41)(42). However, because relatively high concentrations of urea were required to alter AA release and PGE synthesis, and because guanidine had effects on particulate acyl hydrolase activity qualitatively similar to those of urea, the importance of local alterations in urea concentrations in the physiologic regulation of inner medullary PG synthesis and water excretion remains to be determined.…”

“…The influence of Ca2" on PG synthesis may be mediated through an action of this cation to stimulate the release of free arachidonate (AA) from tissue lipid stores (1), a step which appears to be rate limiting in the cellular generation of PG (4). In the renal IM, where osmolality ordinarily varies over a wide range under normal physiologic conditions (5), there is evidence that solute concentration is an important local determinant of PG synthesis (1,(6)(7)(8). Earlier studies from our laboratory indicated that effects of solute concentration on immunoreactive PGE (iPGE) synthesis, analogous to those of Ca2+, are mediated through alterations in the release of AA from tissue lipid stores (1).…”