Bradykinin-induced changes in phosphatidyl inositol turnover in cultured rabbit papillary collecting tubule cells

Interaction of antibodies to proteinase 3 (classic anti-neutrophil cytoplasmic antibody) with human renal tubular epithelial cells: impact on signaling events and inflammatory mediator generation

Among the anti-neutrophil cytoplasmic Abs (ANCA), those targeting proteinase 3 (PR3) have a high sensitivity and specificity for Wegener's granulomatosis (WG). A pathogenetic role for these autoantibodies has been proposed due to their capacity of activating neutrophils in vitro. Recently, PR3 was also detected in human renal tubular epithelial cells (TEC). In the present study, the effect of murine monoclonal anti-PR3 Abs (anti-PR3) and purified c-ANCA targeting PR3 from WG serum on isolated human renal tubular cell signaling and inflammatory mediator release was characterized. Priming of TEC with TNF-alpha resulted in surface expression of PR3, as quantified in immunofluorescence studies and by flow cytometry. Moreover, PR3 was immunoprecipitated on surface-labeled TEC. Primed TEC responded to anti-PR3 with a dose- and time-dependent activation of phosphoinositide hydrolysis, resulting in a remarkable accumulation of inositolphosphates. Control IgG was entirely ineffective, whereas PR3-ANCA reproduced the phosphoinositide response. The signaling response was accompanied by a pronounced release of superoxidanion into the cell supernatant. Moreover, large amounts of PGE(2) and, to a lesser extent, of thromboxane B(2), the stable metabolite of TxA(2), were secreted from anti-PR3-stimulated TEC. In parallel, a rise in intracellular cAMP levels was observed, which was blocked by the cyclooxygenase inhibitor indomethacin. We conclude that anti-PR3 Abs directly target renal TECs, thereby provoking pronounced activation of the phosphoinositide-related signal transduction pathway. Associated metabolic events such as the release of reactive oxygen species and lipid mediators may directly contribute to the development of renal lesions and loss of kidney function in WG.

Effect of protein kinase C activation and down-regulation on active calcium transport

Active transcellular Ca2+ transport in primary cultures of the rabbit kidney collecting system has been shown to be responsive to PTH through activation of protein kinase A (PKA). The present study investigates an additional regulatory pathway activated by protein kinase C (PKC). Cells from rabbit kidney connecting tubules and cortical collecting ducts were isolated by immunodissection and subsequently cultured on permeable filters. Incubation of cultured cells with the PKC activator, 12-O-tetradecanoylphorbol 13-acetate (TPA, 10(-8) to 10(-6) M) had a dual effect on active transcellular Ca2+ transport. Short-term incubation increased membrane-associated PKC activity within 10 minutes and decreased active transcellular Ca2+ transport dose-dependently (IC50 = 3.4 +/- 0.4 nM), with a maximal inhibition of 74 +/- 3%. TPA (10(-7) M) concomitantly inhibited the amiloride-sensitive transepithelial potential difference (p.d.) and short-circuit current across the monolayers. After prolonged exposure to TPA, total cellular PKC activity was down-regulated, resulting in a maximal 65 +/- 5% reduction after one hour. Interestingly, this latter event was temporally separated from a gradual return of both Ca2+ absorption rate and transepithelial p.d. to control levels occurring over 96 and 48 hours, respectively, of further incubation with TPA. The inhibitor of protein kinase activity, staurosporine (10(-7) M), when present during incubation with submaximal concentration of TPA (10(-8) M) partly prevented the TPA-induced inhibition of Ca2+ absorption from 54 +/- 4 to 27 +/- 3%. This study demonstrates for the first time that, in addition to PKA, activation of PKC plays a regulatory role in transcellular Ca2+ reabsorption in the renal collecting system.

Second messenger systems stimulated by bradykinin in osteoblastic cells: evidence for B2 receptors

The effects of bradykinin, analogs and inhibitors on the human osteoblastic osteosarcoma cell lines Saos-2 and G292 and on normal rat calvarial osteoblastic cells were investigated. In all cell types, bradykinin (1 nM-100 microM) caused significant time- and dose-dependent changes in the levels of inositol phosphates. Neomycin inhibited the inositol phosphate response to bradykinin, while indomethacin had no effect. Bradykinin also elicited a dose-dependent increase in free cytosolic calcium concentration. Bradykinin and T-kinin did not affect cyclic AMP levels in these cells. Doses of des-Arg9-bradykinin, a B1 receptor agonist, up to 100 nM did not stimulate the osteoblastic inositol phosphate response. In addition, the bradykinin-stimulated inositol phosphate response was unaffected by des-Arg9-[Leu8]-bradykinin, a B1 receptor antagonist, while it was inhibited by D-Arg-[Hyp3-[beta-(2-thienyl)-Ala]5,8-D-Phe7]-bradykinin, a B2 receptor antagonist. These results suggest that in osteoblastic cells the mechanism of action of bradykinin involves stimulation of the phosphoinositide metabolism and increases in cytosolic calcium levels through activation of B2 receptors.

Cellular mechanisms of bradykinin-induced hyperpolarization in renal epitheloid MDCK-cells

Previous studies have demonstrated that bradykinin hyperpolarizes the cell membrane of subconfluent MDCK cells by increase of the potassium conductance. The present study has been performed to elucidate the intracellular mechanisms involved. To this end, the effects of bradykinin on the potential difference across the cell membrane (PD), on formation of inositol phosphates, and on intracellular calcium concentration (Cai) have been analyzed in cells without or with pretreatment with pertussis toxin or 12-O-tetradecanoylphorbol 13-acetate diester (TPA). In untreated cells, bradykinin leads to a transient increase of inositol 1,4,5-trisphosphate and inositol 1,3,4,5-tetrakisphosphate, increase of Cai, activation of potassium channels and hyperpolarization of the cell membrane. The effects of bradykinin on PD and Cai are still present in the absence of extracellular calcium. In cells pretreated with pertussis toxin the effect of bradykinin on inositol trisphosphate formation is almost abolished but bradykinin still leads to a transient increase of Cai and PD in the presence and absence of extracellular calcium. In cells pretreated with TPA the bradykinin-induced increase of inositol trisphosphate formation is blunted, the bradykinin-induced increase of Cai abolished, but the bradykinin-induced hyperpolarization still present. The observations indicate that bradykinin increases Cai in part by phorbol ester and pertussis toxin sensitive activation of phospholipase C. In addition, bradykinin is capable of enhancing Cai by utilizing pertussis toxin insensitive mechanisms. Furthermore, bradykinin is able to transiently enhance the potassium conductance without a general increase of intracellular calcium.

Bradykinin stimulates production of inositol (1,4,5) trisphosphate in cultured mesangial cells of the rat via a BK2-kinin receptor

1. Using [125I-Tyr0]-BK, as radiolabelled ligand, and various agonists and antagonists of bradykinin (BK) we identified a single class of specific BK2-binding sites in mesangial cell membranes (Bmax = 73 fmol mg-1 protein and Kd = 3.7 nM). 2. Following the addition of 0.1 microM BK, inositol (1,4,5) trisphosphate (IP3) formation increased within 20 s from a basal level of 64 to a maximal value of 175 pmol mg-1 protein. 3. Incubation in a Ca(2+)-free medium did not change IP3 production but a 5 min preincubation with 1 mM EGTA completely prevented the BK-induced IP3 formation, suggesting that IP3 formation is partly dependent on extracellular calcium. 4. The BK2 antagonist D-Arg-Hyp3-D-Phe7-BK (10 microM) but not the BK1 antagonist (des-Arg9-Leu8-BK) abolished IP3 production in response to 0.1 microM BK. Pretreatment of mesangial cells with pertussis toxin was without effect on BK-induced IP3 formation, whereas phorbol 12-myristate 13-acetate significantly enhanced (by 25%) BK-induced IP3 formation. 5. The present data demonstrate that inositol phosphate breakdown in rat mesangial cells can be mediated via activation of a BK2-kinin receptor and is under negative control of protein-kinase C.

Ion transport in cultured epithelia from human sweat glands: comparison of normal and cystic fibrosis tissues

1. Cultured epithelia derived from whole human sweat glands, isolated secretory coils, isolated reabsorptive ducts and whole glands from cystic fibrosis (CF) subjects have been used to examine drug sensitivity by use of short circuit current recording. 2. Short circuit current increases were observed with lysylbradykinin, carbachol and histamine in epithelia of different origins. All responses were due to stimulation of electrogenic sodium absorption, evidenced by the inhibition of these responses by amiloride. The latter also abolished the basal current. The terpenes, thapsigargin and forskolin had no effect on transport. 3. The stimulation of a sodium current by agonists was dependent upon calcium, responses being inhibited by lanthanum ions and EGTA. Further A23187 induced a sodium current. 4. Pronounced oscillations in the sodium currents were a feature of the responses, implying synchronous, regulated cell activity. 5. Forskolin produced a ten fold increase in adenylate cyclase activity. All agonists listed in 2 except forskolin caused an increase in intracellular calcium [Ca]i, [Ca]i responses in CF cells were not different from those of normal cells, except with thapsigargin where the responses were smaller. 6. It is concluded that in culture, cells develop ductal characteristics, whether derived from normal or CF glands, coils or ducts. An increase in [Ca]i followed by activation of calcium-sensitive potassium channels and apical membrane hyperpolarization may be the major mechanism for increasing sodium influx.

AVP stimulates adenylyl cyclase and phospholipase C in reciprocal fashion in cultured RIMCT cells

In cultured rat inner medullary collecting tubule (RIMCT) cells, arginine vasopressin (AVP) stimulates adenylyl cyclase (AC) activity in dose-dependent fashion, with no response at concentrations of 10(-10) M or below and with peak activity at 10(-7) M AVP. In contrast, AVP-stimulated phospholipase (PLC) activity is greatest at concentrations at which there is no effect on AC and decreases at higher concentrations of AVP, becoming undetectable at 10(-7) M. Increasing cellular adenosine 3',5'-cyclic monophosphate (cAMP) content with either exogenous ClPheScAMP or forskolin eliminates inositol trisphosphate production in response to 10(-13) M AVP. Conversely, inhibition of AC by 2',5'-dideoxyadenosine (DDA) unmasks PLC activity in response to 10(-7) M AVP that is not observed in the absence of DDA. Similarly, DDA prevents inhibition of epidermal growth factor-stimulated PLC by AVP. These findings demonstrate the reciprocal relationship between AVP-stimulated AC and PLC activities in cultured RIMCT cells, which may explain previous divergent results regarding the ability of AVP to stimulate PLC in this tissue.

Regulation of cGMP production by intracellular alkalinization in cultured rat inner medullary collecting duct cells

We evaluated the relationship between cell pH and cGMP production in cultured rat renal inner medullary collecting duct cells. The cGMP level, 21 +/- 6, was not different in control vs. alkalinized cells, 49 +/- 17 fmol/mg protein (p greater than 0.5). 10(-11) M atrial natriuretic peptide (ANF) enhanced cGMP production in alkalinized cells, 426 +/- 34 vs. 141 +/- 9*. Conversely, alkalinization inhibited 10(-4)M nitroprusside (SNP) induced cGMP formation, 29 +/- 9 vs. 332 +/- 67*. Phosphodiesterase inhibition abolished the difference in cGMP production by ANF but did not reverse the inhibitory effect of alkalinization on SNP induced cGMP production. In rat renal inner medullary collecting duct cells, cellular alkalinization plays a significant role in the regulation of guanylate cyclase mediated cGMP production. * = p less than 0.05).

Cyclic adenosine monophosphate and diacylglycerol. Mutually inhibitory second messengers in cultured rat inner medullary collecting duct cells

Studies were performed to examine interactions between the adenylyl cyclase (AC) and phospholipase C (PLC) signaling systems in cultured rat inner medullary collecting duct cells. Stimulation of AC by either arginine vasopressin (AVP) or forskolin or addition of exogenous cAMP inhibits epidermal growth factor (EGF)-stimulated PLC. This inhibition is mediated by activation of cAMP-dependent kinase as it is prevented by pretreatment with the A-kinase inhibitor, N-[2-(methylamino)ethyl]-5-isoquinoline-sulfonamide (H8) but not by the C-kinase inhibitor, 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H7). Exposure to EGF eliminates AVP-stimulated cAMP generation. This is not mediated by a cyclooxygenase product as inhibition by EGF is observed even in the presence of the cyclooxygenase inhibitor, flurbiprofen. Inhibition by EGF is not due to an increase in inositol trisphosphate (IP3) as exposure of saponin-permeabilized cells to exogenous IP3 is without effect. Inhibition by EGF is prevented by pretreatment with the C-kinase inhibitor, H7, but not by the A-kinase inhibitor, H8. Exposure to the synthetic diacylglycerol (DAG), dioctanoylglycerol, also inhibits AVP-stimulated AC activity; therefore, inhibition by EGF is due to activation of protein kinase C. Thus, in cultured rat inner medullary collecting duct cells, cAMP and DAG function as mutually inhibitory second messengers with each impairing formation of the other.

Eicosanoid production by isolated glomeruli of rats with unilateral ureteral obstruction

The production of PGE2 6-keto PGF1 alpha and TxB2 under basal conditions and after exposure to angiotensin II was examined in vitro in isolated glomeruli from sham-operated control rats and rats with unilateral ureteral obstruction of 24 hour duration, that were or were not pretreated with an inhibitor of the angiotensin I converting enzyme (ACE). Basal prostanoid production was greater in glomeruli from the obstructed kidney (OK) than in glomeruli from the contralateral kidney (CLK) of rats with obstruction or glomeruli from the kidneys of sham-operated rats. Glomeruli obtained from the CLK of rats with unilateral obstruction also produced more PGE2 and 6-keto PGF1 alpha than glomeruli obtained from kidneys of sham-operated rats. Administration of an ACE inhibitor to rats with unilateral obstruction in vivo returned basal prostanoid production in vitro to levels seen in glomeruli of sham-operated rats. The increase in prostanoid production in response to angiotensin II added in vitro was less in glomeruli from rats with unilateral obstruction than in glomeruli from sham-operated rats. However, the response was restored to that seen in glomeruli of sham-operated rats after blockade of angiotensin II synthesis in vivo in rats with unilateral obstruction. Blockade of angiotensin II synthesis in sham-operated rats did not affect prostanoid synthesis by their glomeruli.(ABSTRACT TRUNCATED AT 250 WORDS)

Receptor-effector coupling by G proteins

The primary structure of G proteins as deduced from purified proteins and cloned subunits is presented. When known, their functions are discussed, as are recent data on direct regulation of ionic channels by G proteins. Experiments on expression of alpha subunits, either in bacteria or by in vitro translation of mRNA synthesized from cDNA are presented as tools for definitive assignment of function to a given G protein. The dynamics of G protein-mediated signal transduction are discussed. Key points include the existence of two superimposed regulatory cycles in which upon activation by GTP, G proteins dissociate into alpha and beta gamma and their dissociated alpha subunits hydrolyze GTP. The action of receptors to catalyze rather than regulate by allostery the activation of G proteins by GTP is emphasized, as is the role of subunit dissociation, without which receptors could not act as catalysts. To facilitate the reading of this review, we have presented the various subtopics of this rapidly expanding field in sections 1-1X, each of which is organized as a self-contained sub-chapter that can be read independently of the others.

Characterization of an in vitro system of human renal papillary collecting duct cells

We have developed an in vitro model of human papillary collecting duct cells isolated from cadaver kidneys using methods similar to those we previously reported for the isolation of human proximal tubule cells. To date we have isolated papillary collecting duct cells from 100 normal human kidneys. Papillae were dissected and digested in Cellgro containing 400 U/ml collagenase. Cells were plated on fibronectin-coated culture flasks at a density of 10(4) live cells/ml in Cellgro supplemented with insulin and 10% fetal bovine serum. Confluent monolayers, which were able to withstand 600 mOSM for 8 h, were obtained within 10 to 15 d. Cells of primary isolates and first passages exhibited epithelial cell ultrastructure including cell junctions, microvilli, and cilia. A dark-brown reaction product was observed in these cells when stained by the immunoperoxidase method with peroxidase-labeled peanut lectin (Arachis hypogaea), which binds specifically to human distal tubule and collecting duct cells. These cells were negative for Factor-VIII (a marker for endothelial cells) and gamma-glutamyltransferase (a marker for proximal tubule cells). High activities of the glycolytic enzyme pyruvate kinase and arginine vasopressin-stimulated cAMP production in these cells are consistent with a distal nephron origin. The results indicate that human collecting duct cells can be isolated and cultured to provide an in vitro system to probe pathogenetic mechanisms of potential nephrotoxins.

Roles of G proteins in coupling of receptors to ionic channels and other effector systems

Guanine nucleotide binding (G) proteins are heterotrimers that couple a wide range of receptors to ionic channels. The coupling may be indirect, via cytoplasmic agents, or direct, as has been shown for two K+ channels and two Ca2+ channels. One example of direct G protein gating is the atrial muscarinic K+ channel K+[ACh], an inwardly rectifying K+ channel with a slope conductance of 40 pS in symmetrical isotonic K+ solutions and a mean open lifetime of 1.4 ms at potentials between -40 and -100 mV. Another is the clonal GH3 muscarinic or somatostatin K+ channel, also inwardly rectifying but with a slope conductance of 55 pS. A G protein, Gk, purified from human red blood cells (hRBC) activates K+ [ACh] channels at subpicomolar concentrations; its alpha subunit is equipotent. Except for being irreversible, their effects on gating precisely mimic physiological gating produced by muscarinic agonists. The alpha k effects are general and are similar in atria from adult guinea pig, neonatal rat, and chick embryo. The hydrophilic beta gamma from transducin has no effect while hydrophobic beta gamma from brain, hRBCs, or retina has effects at nanomolar concentrations which in our hands cannot be dissociated from detergent effects. An anti-alpha k monoclonal antibody blocks muscarinic activation, supporting the concept that the physiological mediator is the alpha subunit not the beta gamma dimer. The techniques of molecular biology are now being used to specify G protein gating. A "bacterial" alpha i-3 expressed in Escherichia coli using a pT7 expression system mimics the gating produced by hRBC alpha k.

Peptide-dependent regulation of epithelial nephron functions

It has become evident that the nephron is an important target organ of many of the regulatory peptides; this brief overview will not attempt to consider the vast amount of work on peptide-dependent kidney functions; instead, it will emphasize recent work directed towards understanding intracellular signal pathways between peptide ligand-receptor interaction and expression of physiological transport responses in renal epithelial cells. The awareness that peptide hormones of differing origin, e.g., intestinal and cardiac, share at least some of the signal steps in nephron cells, has stimulated work on nephron segmental analysis of receptor binding, of second messengers, of membrane G proteins, of protein phosphorylation, and of final membrane transport responses, such as peptide-dependent ion channel regulation. Peptides involved in cell growth and differentiation, e.g., growth factors, appear to act through part of the signal pathway shared by other peptides. The peptides selected for the purpose of this review, then, are those that have been linked, by experimental evidence, to intracellular messenger systems in nephron epithelia.

Enhanced responsiveness to angiotensin II in vascular smooth muscle cells from spontaneously hypertensive rats is not associated with alterations in protein kinase C

This study compares vascular smooth muscle cells from spontaneously hypertensive and normotensive Wistar-Kyoto rats with respect to protein kinase C and intracellular responses to angiotensin II (Ang II). Ang II-induced degradation of polyphosphoinositides and accumulation of inositol di- and tris-phosphates was enhanced (approximately twofold) in hypertensive-derived cells, without a change (vs. normotensive-derived cells) in half-maximally effective concentrations of Ang II. Intracellular pH (approximately 6.6) was comparable between both cell isolates at quiescence, but alkalinization induced by Ang II, serum, or phorbol ester was greater (delta 0.1-0.2 pH units) for hypertensive-derived cells. For both cell types, the intracellular pH response to these agonists was prevented in the presence of Na+-H+ exchange inhibitors. S6 kinase activation induced by Ang II was enhanced (approximately twofold) in hypertensive-derived cells, whereas activation in response to serum or 12-O-tetradecanoylphorbol 13-acetate did not differ significantly between the two cell types. Quantitation of protein kinase C by immunoblotting and [3H]phorbol dibutyrate binding procedures revealed no differences between the two smooth muscle cell isolates (at quiescence or in the presence of serum) with respect to either total amounts or subcellular distribution. Sensitivity of protein kinase C to phorbol ester was apparently also not different between the two cell types, as assessed from dose-dependent (phorbol ester) S6 kinase activation profiles. Phorbol ester caused a similar subcellular redistribution of [3H]phorbol dibutyrate binding in the two cell isolates, but for both, minimal (10%) translocation occurred in response to Ang II. The data suggest that enhanced agonist responsiveness in vascular smooth muscle cells is unlikely to involve alterations in protein kinase C.

Bradykinin stimulated PGE2 production is independent of changes in intracellular calcium in MDCK cells

In order to assess whether changes in intracellular Ca2+ are necessary for bradykinin stimulated activation of phospholipase A2 and PGE2 production, MDCK cells were treated with phorbol myristate acetate (PMA) and Lanthanum (La3+). 100 nM PMA reduced peak BK (1 uM) stimulated Ca2+ to 44.0 +/- 11.4% of control, while 1 mM LaC13 reduced peak Ca2+ to 43.5 +/- 12.2% of control. Addition of both PMA and LaC13 reduced the BK stimulated change in intracellular Ca2+ to 8.3 +/- 1.0% of control. In contrast, La3+ did not reduce PGE2 production in response to 10(-7) M to 10(-5) M BK. PMA stimulated PGE2 production, as shown previously. Addition of both PMA and La3+ at doses capable of reducing Ca2+ changes to less than 10% of normal, failed to block BK induced PGE2 production. Therefore, BK stimulated PLA2 activation and PGE2 production can be dissociated from changes in intracellular Ca2+ and suggest that BK activates PLA2 through a mechanism other than by increases in intracellular Ca2+.

Epidermal growth factor responsiveness in smooth muscle cells from hypertensive and normotensive rats

Aortic smooth muscle cells from spontaneously hypertensive rats (SHR) exhibit inappropriate proliferation characteristics in culture that suggest a modified response to serum mitogens or growth factors. The present study compares vascular smooth muscle cells from SHR and normotensive Wistar-Kyoto (WKY) rats with respect to their proliferative and functional response to growth factors. Specific attention was focused on the interaction of these vascular smooth muscle cells with epidermal growth factor. An increased growth rate of vascular smooth muscle cells from SHR (vs. WKY rats) was observed when cells were cultured in the presence of serum (10% and 0.5%), but not under serum-free conditions. The additional presence of low serum concentrations (0.5%) was required for epidermal growth factor to elicit a proliferative response, whereupon smooth muscle cells from SHR displayed an increased (vs. WKY rats) growth rate. Saturation binding of [125I]epidermal growth factor to intact smooth muscle cells indicated a twofold increase in receptor density in SHR-derived cells (p less than 0.001 vs. WKY rats) without an alteration in affinity for the growth factor. Cells derived from SHR also exhibited greater functional responsiveness to epidermal growth factor when compared with smooth muscle cells from WKY rats as evidenced by amplifications of both S6 kinase activation, phosphoinositide catabolism, elevation of intracellular pH, and DNA synthesis (nuclear labeling). We conclude that increased responsiveness of SHR-derived smooth muscle cells to epidermal growth factor could contribute to alterations in vascular smooth muscle growth and tone that may be fundamental to the pathogenesis of hypertension and atherosclerosis.

Activation of phospholipase A2 by endothelin in cultured vascular smooth muscle cells

The ability of endothelin to promote phospholipid hydrolysis has been studied in myo-[2-3H]-inositol-, [3H]-arachidonic acid- or methyl-[3H]choline chloride-prelabelled cultured vascular smooth muscle cells (VSMC) from rat and bovine thoracic aortae and human omental vessels. The biochemical responses to endothelin were comparable between the different VSMC isolates. Endothelin promoted the accumulation of glycerolphospho[3H]inositol and concomitant loss of [3H]-inositol label from phosphatidylinositol. Exposure of [3H]choline-labelled VSMC to endothelin resulted in a loss of radioactivity from phosphatidylcholine that was inversely parallelled by an increase in water-soluble [3H]-choline metabolites. In [3H]-arachidonic acid ([3H]-AA)-labelled VSMC, endothelin induced extracellular release of [3H]-AA which derived from both phosphatidylcholine and phosphatidylinositol. Half-maximally effective concentrations of endothelin for all these responses were approximately 2-7 nM and did not vary between VSMC types. Endothelin-induced release of [3H]-AA into VSMC medium-overlay was inhibited by quinacrine and nordihydroguaiaretic acid but not by neomycin or indomethacin. The data herein implicate activation of phospholipase A2 by endothelin with subsequent metabolism of arachidonic acid via the lipoxygenase pathway.

Peptide hormones, cytosolic calcium and renal epithelial response

We have reviewed the evidence that a number of hormones interact with renal tubular epithelial cells. The evidence suggests that in the mammalian renal tubule bradykinin and parathyroid hormone interact with cell surface receptors to initiate the hydrolysis of PIP2 leading to the formation of I 1,4,5P3 and diacylglycerol in the distal and proximal tubule, respectively. The activation of this second messenger system leads to the mobilization of Ca2+ from intracellular stores. Vasopressin does not activate this second messenger system in mammalian renal epithelial cells, and we cannot demonstrate I 1,4,5P3 formation and Ca2+ mobilization either in the rabbit papillary collecting tubules or in MDCK cells. There is evidence emerging, but not discussed here, that angiotensin II may also mediate some of its effects on the mammalian proximal tubule via the inositol polyphosphate second messenger system.

Bradykinin (BK) enhances diuresis and natriuresis in saline volume-expanded dogs

15 micrograms bradykinin was given with large amount of physiological saline solution intravenously to dogs. Significantly greater diuresis and natriuresis were obtained compared with those of simple saline volume expansion experiments. Bradykinin in small doses which were selected as giving no influence on blood pressure enhanced additively diuresis and natriuresis, similarly with subpressor doses of A II, AVP, and MX in saline volume expanded dogs. Since all four agents are having cellular Ca-mobilizing action in common, it is suggested that phosphoinositide system may be involved in this enhancement of renal sodium and water excretion.

Endothelin stimulates phospholipase C in cultured vascular smooth muscle cells

Cultured vascular smooth muscle cells from bovine and rat thoracic aortae and from human omental vessels have been examined for cellular responses to endothelin. In myo-[3H]-inositol-prelabelled cells endothelin induced a rapid (within 30 sec) and protracted increase of [3H]-inositol content in inositol bis- and tris-phosphates. Concomitantly, significant polyphosphoinositide hydrolysis occurred within 30 sec. Accumulation of [3H]-inositol monophosphate and hydrolysis of phosphatidylinositol were delayed. In cells prelabelled with [3H]-arachidonic acid endothelin promoted rapid production of [3H]-diacylglycerol which decayed slowly toward control values after reaching maximum levels (1-2 min). Half-maximally effective concentrations of endothelin for all these cellular responses were comparable (approximately 3-7 nM) and not significantly different between the vascular cell isolates. The involvement of the phospholipase C-signal transduction pathway in mediating endothelin-induced vasoconstriction is invoked.

Rapid action of 1,25-dihydroxyvitamin D3 on hepatocyte phospholipids

Recent studies have reported cellular effects of 1,25-dihydroxyvitamin D3 within 15 minutes, a time period too rapid to be mediated by nuclear activation. The vitamin increases hepatocyte cytosolic calcium levels in the absence of extracellular calcium within 5 minutes. Since metabolites of phosphatidylinositol have been implicated as second messengers in the regulation of cytosolic calcium, we examined the effect of 1,25-dihydroxyvitamin D3 on hepatocyte phosphatidylinositol turnover and compared these effects to those produced by vasopressin. In isolated hepatocytes labeled with [3H]inositol, 1,25-dihydroxyvitamin D3 (4 nM) increased [3H]glycerophosphorylinositol by 16% (p less than 0.01) within 2.5 minutes, by 18% (p less than 0.01) after 5 minutes, and by 11% (p less than 0.05) after 10 minutes. At a concentration of 20 nM, 1,25-dihydroxyvitamin D3 increased [3H]glycerophosphorylinositol by 27% (p less than 0.01) after 5 minutes. Vitamin D did not affect [3H]inositol polyphosphates. Conversely, vasopressin had no effect on [3H]glycerophosphorylinositol but significantly increased [3H]inositol phosphate, [3H]inositol bisphosphate, and [3H]inositol triphosphate. 1,25-Dihydroxyvitamin D3 (4 nM) decreased [3H]phosphatidylinositol by 10% (p less than 0.05) after 5 minutes and by 16% (p less than 0.01) after 10 minutes. At a concentration of 20 nM, 1,25-dihydroxyvitamin D decreased [3H]phosphatidylinositol by 18% (p less than 0.01) after 5 minutes. The vitamin did not affect [3H]phosphatidylinositol bisphosphate or [3H]phosphatidylinositol trisphosphate. 24,25-Dihydroxyvitamin D had no effect on inositol phospholipids. The effects of 1,25-dihydroxyvitamin D3 on inositol phospholipids were blocked by quinacrine. Bromophenacylbromide inhibited the effects of 1,25-dihydroxyvitamin D3 on inositol phospholipids and also blocked the vitamin-induced increments in cytosolic calcium.(ABSTRACT TRUNCATED AT 250 WORDS)

Human eccrine sweat gland epithelial cultures express ductal characteristics

1. Isolated human eccrine sweat glands were cultured in vitro. Cells were harvested and plated onto permeable supports to form confluent cell sheets, area 0.2 cm2. These were used to study the electrogenic transepithelial transport of ions by measurement of short-circuit current (SCC). Epithelial sheets had a basal SCC of 5.89 +/- 0.62 microA cm-2 (n = 33) and a transepithelial resistance of 74.1 +/- 5.6 omega cm2 (n = 33). The transepithelial potential difference varied between -0.2 and -1.8 mV with a mean value of -0.71 +/- 0.09 mV (n = 33). 2. The basal current was abolished by addition of 10 microM-amiloride to the apical bathing solution. The concentration of amiloride which inhibited basal SCC by 50% (EC50) was 0.4 microM. Cultures prepared from the secretory coil of sweat glands, rather than from whole glands, were similarly sensitive to amiloride (EC50 = 0.8 microM). 3. Lysylbradykinin (LBK), carbachol, isoprenaline, prostaglandin E2 (PGE2) and A23187 all increased SCC in cultures from whole glands. LBK responses were obtained with basolateral and not with apical application. Furthermore LBK actions were not substantially altered by cyclo-oxygenase inhibition but showed marked desensitization upon repeated application. Sheet cultures prepared from sweat gland coils also showed SCC responses to both carbachol and LBK. Forskolin, an activator of adenylate cyclase, did not alter SCC in either type of preparation. 4. Replacement of chloride and of chloride and bicarbonate in the bathing solution did not cause attenuation of the responses to LBK or carbachol in whole-gland sheet cultures. Furthermore responses were unaffected by piretanide or acetazolamide. These results were taken to indicate that anion secretion was not the basis for the SCC responses. 5. Responses to LBK and carbachol were significantly reduced by amiloride (10 microM), this effect being reversible. No responses to LBK or carbachol were seen when N-methyl-D-glucamine (NMDG) was used to replace sodium, whereas reintroduction of sodium ions restored responsiveness to these agents. 6. The SCC responses to the muscarinic agonist carbachol and to LBK appear to be due to stimulation of amiloride-sensitive, electrogenic sodium absorption in whole-gland sheet cultures. Further it would appear that, in culture, the pleuripotential capacity of the cells is revealed since both whole-gland and secretory coil cultures exhibit some properties usually associated in vivo with duct cells. Many mammalian epithelia show electrogenic chloride secretion both in response to carbachol and LBK but also in response to activation of adenylate cyclase with forskolin.(ABSTRACT TRUNCATED AT 400 WORDS)

Localization and regulation of the renal kallikrein kinin system: possible relations to renal transport functions

The complete renal kallikrein kinin system has recently been localized in defined nephron segments. Kallikrein was found to be formed and secreted by connecting tubule cells in the late distal convoluted tubule, whereas kininogen and a novel kininase were located in collecting tubules. Kinins were shown to act on collecting tubule as well as medullary interstitial cells and the renal vasculature. The literature on interactions of this system with renal sodium transport is conflicting. Renal and urinary kallikrein was found to be increased under sodium restricted conditions, whereas kinin has a diuretic and natriuretic effect in the collecting tubule, when added from the basolateral surface. On the other hand renal kallikrein activity and connecting tubule cell morphology change in parallel with dietary potassium load indicating a coupling to potassium secretion. The possible role of the renal kallikrein kinin system in regulating collecting tubule function by tubular and vascular effects is outlined in spite of many open questions which remain to be answered.

Bradykinin-activated membrane-associated phospholipase C in Madin-Darby canine kidney cells

Previous studies have demonstrated that bradykinin stimulates the rapid release of inositol 1,4,5 trisphosphate (IP3) from membrane phosphatidylinositol 4,5 bisphosphate (PIP2) in Madin-Darby canine kidney (MDCK) cells. Since current evidence would suggest that the activation of phospholipase C (PLC) is mediated through a guanine nucleotide-binding protein in receptor-mediated activation of PLC, we evaluated the role of guanine nucleotide proteins in receptor-mediated (bradykinin-stimulated) activation of PLC in MDCK cells. Bradykinin at 10(-7) M produced a marked increase in IP3 formation within 10 s increasing from a basal level of 46.2 to 686.6 pmol/mg cell protein a 15-fold increase. Pretreatment of MDCK cells in culture with 200 ng/ml of pertussis toxin for 4 h reduced the bradykinin-stimulated response to 205.8 pmol/mg protein. A 41-kD protein substrate in MDCK membranes was ADP ribosylated in vitro in the presence of pertussis toxin. The ADP ribosylation in vitro was inhibited by pretreatment of the cells in culture with pertussis toxin. Membranes from MDCK cells incubated in the presence of [3H]PIP2/phosphatidyl ethanolamine liposomes demonstrated hydrolysis of [3H]PIP2 with release of [3H]IP3 when GTP 100 microM or GTP gamma S 10 microM was added. Bradykinin 10(-7) M added with GTP 100 microM markedly increased the rate of hydrolysis within 10 s, thus demonstrating a similar time course of PLC activation as intact cells. These results demonstrate that bradykinin binds to its receptor and activates a membrane-associated PLC through a pertussis toxin-sensitive, guanine nucleotide protein.

Calcium and cyclic adenosine monophosphate as second messengers for vasopressin in the rat inner medullary collecting duct

Vasopressin increases both the urea permeability and osmotic water permeability in the terminal part of the renal inner medullary collecting duct (terminal IMCD). To identify the second messengers that mediate these responses, we measured urea permeability, osmotic water permeability, intracellular calcium concentration, and cyclic AMP accumulation in isolated terminal IMCDs. After addition of vasopressin, a transient rise in intracellular calcium occurred that was coincident with increases in cyclic AMP accumulation and urea permeability. Half-maximal increases in urea permeability and osmotic water permeability occurred with 0.01 nM vasopressin. The threshold concentration for a measurable increase in cyclic AMP accumulation was approximately 0.01 nM, while measurable increases in intracellular calcium required much higher vasopressin concentrations (greater than 0.1 nM). Exogenous cyclic AMP (1 mM 8-Br-cAMP) mimicked the effect of vasopressin on urea permeability but did not produce a measurable change in intracellular calcium concentration.

CONCLUSIONS

(a) Cyclic AMP is the second messenger that mediates the urea permeability response to vasopressin in the rat terminal IMCD. (b) Vasopressin increases the intracellular calcium concentration in the rat terminal IMCD, but the physiological role of this response is not yet known.

Protein kinase C modulates phospholipase C and increases arachidonic acid release in bradykinin stimulated MDCK cells

The tumor promoter phorbol ester (PMA) has been shown to stimulate protein kinase C (PKC) in MDCK cells. At the concentrations that produce stimulation of PKC, PMA (100 microM) inhibits BK-induced I1,4,5P3 (IP3) formation and calcium transients in these cells. 1-5-isoquinolinyl-2-methyl-piperazine (H7) a known inhibitor of PKC in MDCK cells reverses the effect of PMA on BK-stimulated IP3 formation and Ca2+ transients in these cells. PMA also stimulates arachidonate release which can be inhibited by preincubation with H7. A dual mechanism of regulation by PKC at the level of phospholipase C (down regulation) and phospholipase A2 (stimulation) is suggested in these cells.

Atrial natriuretic peptide induces breakdown of phosphatidylinositol phosphates in cultured vascular smooth-muscle cells

Discrepancies exist between extent of guanylate cyclase activation by atrial natriuretic peptide (ANP) in cell-free systems and ANP-stimulated levels of cyclic GMP in whole cells, and also between receptor affinity and dose effectiveness of ANP. Therefore, we have investigated whether, in addition to receptor-coupled guanylate cyclase activation, other second-messenger cascade systems may be involved in mediating both an increase in cyclic GMP and the physiological response to ANP. Equilibrium 125I-ANP binding studies on cultured thoracic aorta smooth muscle cells revealed the existence of low-affinity (approximately 10(-8) M, 84.5 fmol/10(5) cells) and high-affinity (approximately 10(-10) M, 12.5 fmol/10(5) cells) binding sites. We confirm that ANP elevates intracellular cyclic GMP (EC50 approximately 10(-8) M) and inhibits agonist-(isoproterenol and forskolin)-induced increases in intracellular cyclic AMP (IC50 approximately 10(-9) M). ANP also stimulated breakdown of phosphatidylinositol phosphates and generation of inositol phosphates with a half-maximally effective concentration of approximately 10(-10) M. The extent of phosphatidylinositol polyphosphate hydrolysis was small (120%) in comparison to that of phosphatidylinositol (Ptd-Ins) (200%). Ptd-Ins hydrolysis was paralleled by the appearance of glycerophosphoinositol, and there was also a close temporal relationship between these processes and the accumulation of intracellular cyclic GMP. Smooth muscle cells released [3H]arachidonic acid label in response to ANP (EC50 approximately 10(-10) M). Taken together, the data suggest that the vasorelaxant hormone ANP has stimulatory effects on phosphoinositol lipid metabolism via both phospholipase C (generation of inositol phosphates) and phospholipase A2 (generation of releasable [3H]arachidonic acid and indirectly glycerophosphoinositol). In contrast, stimulation of phosphatidylinositol phosphate breakdown by the vasoconstrictive hormone angiotensin II is not associated with glycerophosphoinositol formation, and neither cyclic GMP nor cyclic AMP levels were influenced by this hormone.

Relationship between phospholipase C activation and prostaglandin E2 and cyclic adenosine monophosphate production in rabbit tubular epithelial cells. Effects of angiotensin, bradykinin, and arginine vasopressin

By employing early-passaged rabbit kidney epithelial cells in tissue culture, we demonstrated that angiotensin II (AII) has unique mechanisms of signal transduction. First, unlike its action in other target tissues, micromolar concentrations of AII are required to induce small rises in cytosolic calcium, [Ca2+]i, an action which is not accompanied by the release of inositol phosphates (IP). In contrast, nanomolar bradykinin (BK) mobilizes [Ca2+]i through activation of phospholipase C and release of IP. Neither of these stimulated calcium responses exhibits pertussis toxin (PTx) sensitivity. Secondly, AII and BK at 10(-9) to 10(-7) M stimulate cAMP indirectly through PGE2 production in distal cells. AII- and BK-stimulated PGE2 release is PTx inhibitible, suggestive of the presence of a GTP binding protein mediating the response. By contrast, arginine vasopressin fails to elicit rises in [Ca2+]i but exerts its primary effect on cAMP production in distal cells via direct coupling to a stimulatory GTP binding protein, as evidenced by uncoupling with cholera toxin. Regulation of PGE2 synthesis appears to occur via phospholipase A2, not C, by all three peptides.

The separation of myo-inositol phosphates by ion-pair chromatography

The separation of myo-inositol phosphates by ion pair, reverse-phase high performance liquid chromatography has been investigated. The retention of the inositol phosphates is dependent on both the polarity of the hetaeron utilized and on the pH of the solvent. A method is presented which permits the isocratic separation of multiple forms of inositol phosphates including isomers of myo-inositol trisphosphate. This method appears to be superior to the anion exchange based systems currently employed because of smaller retention volumes, the low ionic strength of the solvent employed, the absence of a requirement for reequilibration, and the ability to perform separations isocratically.

Protein kinase C activators and bradykinin selectively inhibit vasopressin-stimulated cAMP synthesis in MDCK cells

To evaluate a possible modulation by protein kinase C of hormonal, cAMP-mediated effects on renal epithelial cells, we studied the effect of protein kinase C activators and of bradykinin on intracellular cAMP accumulation in MDCK cells. A 15-min pretreatment of cells with phorbol 12-myristate 13-acetate or 1-oleoyl-2-acetylglycerol induced a dose-dependent inhibition of vasopressin-stimulated cAMP synthesis, but not of basal or glucagon-, prostaglandin E2-, and forskolin-stimulated cAMP generation. 4 alpha-Phorbol 12,13-didecanoate, inactive on protein kinase C, did not affect cAMP accumulation. Bradykinin (0.1-10 microM) also inhibited the stimulatory effect of vasopressin on cAMP synthesis in a concentration-dependent manner, but affected neither basal cAMP content, nor its stimulation by glucagon, prostaglandin E2 and forskolin. The effect of activators of protein kinase C and of bradykinin occurred while renal prostaglandin synthesis was blocked with indomethacin. The inhibitory effect of protein kinase C activators and bradykinin on cAMP generation was reversed by the protein kinase C inhibitor H7, was enhanced by monensin, one effect of which is to block the recycling of membrane receptors, and persisted when the GTP-binding protein N1 was blocked with 1 mM Mn2+. Our data suggest that: protein kinase C can modulate the tubular effects of vasopressin by inhibiting cAMP generation; this effect is not mediated by renal prostaglandins, and might result from a direct action on the vasopressin receptor, or on its coupling with Ns; the modulation by bradykinin of vasopressin effects are likely to be exerted, at least partly, through activation of protein kinase C.

Bradykinin-stimulated changes in inositol phosphate mass in renal papillary collecting tubule cells

The effect of bradykinin on changes in the chemical levels of myo-inositol polyphosphates in renal papillary collecting tubules was investigated. Myo-inositol phosphate mass was determined by means of an enzymatic, fluorometric assay. Bradykinin induced increases in myo-inositol mono-, bis-, and trisphosphate which were both time and concentration dependent. Furthermore, the magnitude of the chemical levels of myo-inositol monophosphate formed were unlikely to be accounted for solely by the formation and degradation of myo-inositol trisphosphate. These observations are consistent with the concomitant hydrolysis of phosphatidylinositol and phosphatidylinositol bisphosphate. This study also confirms, in freshly isolated renal tubules, observations regarding bradykinin-induced phosphatidylinositol bisphosphate hydrolysis made previously in radiolabeled cultures.

Evidence that bradykinin stimulates renal prostaglandin synthesis by a mechanism distinct from that of other vasoactive substances

Arginine-vasopressin (AVP), angiotensin II (AII), and norepinephrine (NE) are known to stimulate prostaglandin (PG) synthesis in the intact rat kidney perfused with Tyrode's solution by a mechanism that requires intracellular Ca2+, while PG synthesis elicited by bradykinin (BK) is independent of Ca2+. To elucidate further the differences in the mechanism of action of BK and other vasoactive agents, in this preparation we have investigated the effect of caffeine, an agent known to interfere with the uptake and storage of Ca2+ in intracellular sites, on renal output of PGE2 and 6-keto-PGF1 alpha elicited by AVP, AII, NE, and BK; various combinations of the maximal doses of BK, AII, AVP, and NE on renal PG synthesis; and RHC 80267, an inhibitor of diglyceride and monoglyceride lipase, on the output of PGs produced by these vasoactive agents. Infusion of 1 mM caffeine inhibited PG output elicited by AVP, AII, and NE but not that caused by BK in the absence of extracellular Ca2+. Combined administration of maximal doses of BK (2.8 nmol) with that of AII (0.28 nmol), AVP (0.27 nmol), or NE (3.2 nmol) but not AVP and AII, NE and AVP, or NE and AII produced an additive effect on renal PG output in the presence or absence of Ca2+. The renal vasoconstrictor effect of AVP, AII, and NE produced in the presence of Ca2+ was not additive and remained unaltered when given together with BK.(ABSTRACT TRUNCATED AT 250 WORDS)

Vasopressin does not hydrolyze polyphosphoinositides in rabbit papillary collecting tubule cells

Changes in phosphatidylinositol metabolism are suggested to be involved in the mechanism of action of many membrane active hormones. We studied the effect of vasopressin on polyphosphoinositide metabolism in rabbit papillary collecting tubule cells to assess if the hydrolysis of these phospholipids is involved in transmembrane signaling. Rabbit papillary collecting tubule cells grown in monolayers for 5 days were labeled to constant specific activity with [3H]inositol. The temporal changes in [3H]inositol-labeled phospholipids were assessed in response to vasopressin. Similarly, water-soluble inositides were monitored after separation by ion exchange chromatography. Intracellular Ca2+ was monitored by use of the fluorescent indicator dye, quin2. Vasopressin (10(-7) M) did not increase the hydrolysis of phosphoinositides over a 5 min period when compared with controls. Similarly, there was no increase in water-soluble phosphoinositols during the same interval. Pretreating the cells with LiCl (10 mM) did not produce any increase in inositol 1-phosphate when stimulated with vasopressin but did in response to bradykinin. Finally, vasopressin did not increase cytosolic Ca2+ and did not increase the release of prostaglandin E2 into the media under our experimental conditions. We conclude that vasopressin does not stimulate prostaglandin E2 in rabbit papillary collecting tubule cells, does not initiate hydrolysis of polyphosphoinositides and does not increase cytosolic Ca2+. Thus these cells lack V1 receptor coupling mechanisms.

Enzymatic fluorometric assay for myo-inositol trisphosphate

The determination of myo-inositol trisphosphate by an enzymatic fluorometric assay is presented. The method involves the acid extraction of water-soluble inositol polyphosphates followed by separation by anion-exchange chromatography. Samples are subsequently neutralized by passage over a Dowex Cl- resin and elution with lithium chloride. Samples are then desalted with ethanol. Following dephosphorylation with alkaline phosphatase, free myo-inositol is measured enzymatically via the NAD-dependent oxidation to scyllo-inosose with myo-inositol dehydrogenase. The efficiency of recovery, assay specificity, and an application to the measurement of inositol polyphosphates in hormone-stimulated tissue are discussed.

Effects of bradykinin on electrical properties of Madin-Darby canine kidney epithelioid cells

In the present study we have investigated the influence of bradykinin on the potential difference across the cell membrane (PD) of Madin Darby Canine Kidney (MDCK)-cells. In the absence of bradykinin PD averages -52.6 +/- 0.9 mV (n = 52). Increasing extracellular potassium concentration from 5.4 to 10 and 20 mmol/l depolarizes the cell membrane by +5.2 +/- 0.3 mV (n = 8) and +14.9 +/- 1.0 mV (n = 9), respectively. The application of 0.1 mumol/l bradykinin leads to a transient hyperpolarization of the cell membrane to -70.3 +/- 0.6 mV (n = 30). During this transient hyperpolarization increasing extracellular potassium concentration from 5.4 to 10 and 20 mmol/l depolarizes the cell membrane by +10.4 +/- 0.7 mV (n = 10) and +29.2 +/- 0.8 mV (n = 8) respectively. Application of fragments of bradykinin (0.1 mumol/l) are without significant effect on the potential difference across the cell membrane. 1 mmol/l barium depolarizes the cell membrane by +15.8 +/- 1.2 mV (n = 9) and abolishes the effect of step increase of extracellular potassium concentration from 5.4 to 10 mmol/l. In the presence of barium, bradykinin leads to a transient hyperpolarization by -24.7 +/- 1.3 mV (n = 7). During this transient hyperpolarization, the cell membrane is sensitive to extracellular potassium concentration despite the continued presence of barium. In the nominal absence of extracellular calcium, bradykinin leads to a transient hyperpolarization, which can be elicited only once. The transient hyperpolarization is not affected by the presence of verapamil or indomethacin. In conclusion, bradykinin hyperpolarizes MDCK-cells by increasing the apparent potassium conductance.(ABSTRACT TRUNCATED AT 250 WORDS)

Bradykinin-induced changes in inositol trisphosphate mass in MDCK cells

Bradykinin produces increases in cytosolic calcium in MDCK cells. We have extracted and separated Inositol 1,4,5 trisphosphate by HPLC and after-acid hydrolysis and conversion to the hexatrifluoro-acetyl derivative quantitated by negative ion chemical ionization mass spectrometry the mass of inositol trisphosphate in MDCK cells. Bradykinin causes an increase in the mass of Inositol trisphosphate from basal levels of 152 pmoles/mg cell protein to 537 pmoles/mg cell protein by 10 secs of stimulation. We conclude that bradykinin stimulates PLC hydrolysis of PIP2 with rapid release of IP3 in sufficient amount to account for the increase in cytosolic Ca++.

Bradykinin-induced changes in myo-inositol 1,2-(cyclic)phosphate in rabbit papillary collecting tubule cells

Rabbit renal papillary collecting tubule cells were harvested and grown in primary cultures. When labeled with myo-[2-3H]inositol and extracted under neutral conditions, a metabolite undetected under acidic extraction was observed on resolution by anion-exchange chromatography and which eluted under similar conditions with authentic DL-myo-inositol 1,2-(cyclic)phosphate; the mass spectrum of its pentakis(trimethylsilyl) derivative contains an identical ratio of selected ion fragments to the authentic standard. Bradykinin, demonstrated previously to increase labeling of free inositol polyphosphates, increases labeling of inositol 1,2 cyclic phosphate but over a time course subsequent to the formation of inositol trisphosphate. These observations are consistent with the model that bradykinin induces hydrolysis of phosphatidylinositol 4,5-bisphosphate which precedes hydrolysis of phosphatidylinositol in renal papillary collecting tubule cells.

Renal prostaglandin synthesis. Sites of production and specific actions of prostaglandins

Prostaglandins are substances that exert their effects at the site of their production. Therefore, the synthesis and effects of prostaglandins have to be considered separately for each nephron segment. In the cortex, major sites of prostaglandin synthesis include arteries and arterioles as well as the glomerulus. At these sites, prostaglandins are important in maintaining blood flow and glomerular filtration, especially during conditions of enhanced vasoconstrictor activity. Vasoconstrictors such as angiotensin II, norepinephrine, and vasopressin increase production of the vasodilator prostaglandins, thereby preventing an overshoot of their action. The role of arteriolar-glomerular prostaglandins in maintaining blood flow and filtration may be even more prominent during renal diseases. The proximal tubule and the loop of Henle show little ability to produce prostaglandins, but may generate considerable amounts of epoxygenase products of arachidonic acid. These epoxygenase products may play a prostaglandin-independent role in water and electrolyte transport in the thick ascending loop of Henle and the collecting tubule. Both the cortical and the medullary collecting tubules produce large amounts of prostaglandins, predominantly prostaglandin E2 (PGE2). In these segments, synthesis of PGE2 is stimulated by bradykinin and to a somewhat more variable degree by vasopressin. The PGE2 generated antagonizes the hydroosomotic effect of vasopressin both in vivo and in vitro, and may influence electrolyte excretion. Thus, the overall role of PGE2--and possibly of epoxygenase products of arachidonic acid--in tubular functions seems to be one of local modulation of water and electrolyte transport. Finally, interstitial cells are a major site of medullary prostaglandin production. Prostaglandins generated by the interstitial cells may play a role in maintaining blood flow to this poorly oxygenated and hypertonic region of the kidney.

Biochemistry and pharmacology of renal arachidonic acid metabolism

Arachidonic acid is metabolized to prostaglandin, lipoxygenase products, and products of the microsomal cytochrome P-450 enzymes of the kidney. The distribution of the metabolizing enzymes and their regulation and pharmacologic manipulation are reviewed. The mechanisms of release of arachidonic acid from membrane lipids through a surface-mediated receptor mechanism are also discussed. The localization of the various enzymes and product formation may have profound effects on glomerular filtration, renal blood flow, and electrolyte excretion. Therefore, an understanding of the potential sites of inhibition of the nonsteroidal anti-inflammatory drugs is important in assessing their effects on renal function.