Double-barreled K+-selective microelectrodes based on dibenzo-18-crown-6

A four-electrode method to study dynamics of ion activity and transport in skeletal muscle fibers

Ion movements across biological membranes, driven by electrochemical gradients or active transport mechanisms, control essential cell functions. Membrane ion movements can manifest as electrogenic currents or electroneutral fluxes, and either process can alter the extracellular and/or intracellular concentration of the transported ions. Classic electrophysiological methods allow accurate measurement of membrane ion movements when the transport mechanism produces a net ionic current; however, they cannot directly measure electroneutral fluxes and do not detect any accompanying change in intracellular ion concentrations. Here, we developed a method for simultaneously measuring ion movements and the accompanying dynamic changes in intracellular ion concentrations in intact skeletal muscle fibers under voltage or current clamp in real time. The method combines a two-microelectrode voltage clamp with ion-selective and reference microelectrodes (four-electrode system). We validate the electrical stability of the system and the viability of the preparation for periods of ∼1 h. We demonstrate the power of this method with measurements of intracellular Cl-, H+, and Na+ to show (a) voltage-dependent redistribution of Cl- ions; (b) intracellular pH changes induced by changes in extracellular pCO2; and (c) electroneutral and electrogenic Na+ movements controlled by the Na,K-ATPase. The method is useful for studying a range of transport mechanisms in many cell types, particularly when the transmembrane ion movements are electrically silent and/or when the transport activity measurably changes the intracellular activity of a transported ion.

Renal gene expression profiling using kinin B1 and B2 receptor knockout mice reveals comparable modulation of functionally related genes

The kinin B2 receptor, which is constitutively expressed in a large number of tissues, mediates most of the known effects of bradykinin (BK). Normally undetectable in healthy tissues, the B1 receptor is strongly over-expressed under pathological conditions. BK is an important mediator in renal homeostasis and is mainly known for its natriuretic and vasodilatory effects. Recent data evidenced a role for BK in many other biological processes, such as apoptosis, development, extracellular matrix regulation and angiogenesis. In a first step to better understand how BK and its receptors could be involved in such a large variety of biological effects, we used microarray analysis to identify, under physiological conditions, the global renal gene expression profile in mice lacking either the kinin B1 or B2 receptor. Microarray experiments were performed using Agilent Mouse Oligonucleotide Microarrays (21 000 genes/microarray). Interestingly, there was a considerable number of mostly downregulated genes in both BK null mouse models compared with wild-type mice. Furthermore, a number of genes that are known to be implicated in renal physiology and/or pathology were differentially expressed in the BK null mice, which is indicative of the important role of both BK receptors in renal function.

Kallikrein gene delivery attenuates hypertension and cardiac hypertrophy and enhances renal function in Goldblatt hypertensive rats

To demonstrate potential therapeutic effects of kallikrein gene delivery, we delivered adenovirus (Ad.CMV-cHK) carrying the human tissue kallikrein gene into two-kidney, one-clip Goldblatt hypertensive rats. A single intravenous injection of the recombinant adenovirus caused a delay of blood pressure increase that began 1 day after injection and continued for 24 days. A maximal blood pressure reduction was observed in rats receiving kallikrein gene delivery compared with control rats receiving Ad.CMV-LacZ (160+/-5 versus 186+/-7 mm Hg, n=6, P<.01). The expression of human tissue kallikrein mRNA was identified in the kidney, heart, aorta, and liver of rats receiving kallikrein gene delivery. Immunoreactive human kallikrein levels were measured in rat serum and urine in a time-dependent manner. Adenovirus-mediated kallikrein gene delivery caused a significant reduction in the left ventricular mass and cardiomyocyte size, as well as an increase in renal blood flow, urine flow, glomerular filtration rates, electrolyte output, and urine excretion. Enhanced renal responses were accompanied by significant increases in urinary kinin, nitrite/nitrate, and cyclic GMP levels. These findings show that the expression of human tissue kallikrein via gene delivery has protective effects against renovascular hypertension and cardiovascular and renal dysfunction.

Effects of bradykinin and icatibant on renal hemodynamics in conscious spontaneously hypertensive and normotensive rats

We investigated the effects of bradykinin (BK) and icatibant (HOE 140), a highly selective bradykinin-B2-receptor antagonist, on mean arterial blood pressure (MAP), heart rate (HR), renal blood flow (RBF), and renal vascular resistance (RVR) in conscious Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHRs). Experiments were performed in conscious male WKY rats and SHRs instrumented over the long term with arterial and venous catheters and a transit-time flow probe for measurement of RBF. In WKY rats (n = 16), intraaortic (i.a.) bolus injections of BK (0.1, 1.0, and 10 microg) produced dose-dependent decreases in MAP and RBF with reciprocal increases in RVR. Intrarenal (i.r.) injections of BK (10 microg; n = 6) induced the same hemodynamic response pattern, although the increase in RVR was higher compared with i.a. injections (p < 0.05). Neither vasopressin V1-receptor nor alpha1-adrenoceptor blockade had an effect on the renal vasoconstrictor responses on i.a. BK. The i.a. injections of icatibant (0.1, 1.0, 5.0, and 10 microg; n = 6-10 for each dose) led to a dose-dependent blockade of the hemodynamic responses to BK (10 microg, i.a.). Icatibant (10 microg, i.a) had no effect on resting MAP and HR but induced a biphasic response in RBF and RVR with significant changes compared with basal values (p < 0.05). In SHRs (n = 9), after injection of increasing i.a. doses of BK (0.1, 1.0, and 10 microg), dose-dependent decreases in MAP were proportionately greater compared with those in WKY rats. In contrast to WKY rats, RBF and RVR exhibited a biphasic response pattern on BK in SHRs. Neither vasopressin V1-receptor nor alpha1-adrenoceptor blockade had an effect on the renal vasoconstrictor responses on i.a. BK. The i.a. injections of icatibant (10 microg) almost completely blocked the hemodynamic responses on BK in SHRs (n = 13). Icatibant (10 microg, i.a.) itself induced an increase in resting MAP and HR (p < 0.05) and a biphasic response in RBF and RVR with significant changes of basal values (p < 0.05). Our results provide evidence that BK exhibits renal vasoconstrictor and vasodilator properties in vivo, both mediated by B2-receptors. Furthermore, we demonstrated that SHRs display an increased B2-receptor-mediated vasodilatory responsiveness to BK. Finally we showed that blockade of B2 receptors leads to an increase of MAP in SHRs in contrast to WKY rats, suggesting an important role of the kallikrein/kinin system in the regulation of high blood pressure in SHRs.

Bradykinin B2 receptor modulates renal prostaglandin E2 and nitric oxide

Bradykinin and lys-bradykinin generated intrarenally appear to be important renal paracrine hormones. However, the renal effects of endogenously generated bradykinin are still not clearly defined. In this study, we measured acute changes in renal excretory and hemodynamic functions and renal cortical interstitial fluid levels of bradykinin, prostaglandin E2, and cGMP in response to an acute intrarenal arterial infusion of the bradykinin B2 receptor antagonist Hoe 140 (icatibant), cyclooxygenase inhibitor indomethacin, or nitric oxide synthase inhibitor N(G)-monomethyl-L-arginine (L-NMMA) given individually or combined in uninephrectomized, conscious dogs (n=10) in low sodium balance. Icatibant caused a significant decrease in urine flow, urinary sodium excretion, and renal plasma flow rate (each P<.001). Glomerular filtration rate did not change during icatibant administration. Icatibant produced an unexpected large increase in renal interstitial fluid bradykinin (P<.0001) while decreasing renal interstitial fluid prostaglandin E2 and cGMP (each P<.001). Both indomethacin and L-NMMA when given individually caused significant antidiuresis and antinatriuresis and decreased renal blood flow (each P<.001). Glomerular filtration rate decreased during L-NMMA administration (P<.001) and did not change during indomethacin administration. Combined administration of icatibant and indomethacin or L-NMMA caused significant decreases in renal excretory and hemodynamic functions, which were not different from changes observed with icatibant alone. The failure of icatibant to change renal function after inhibition of cyclooxygenase and nitric oxide synthase activity suggests that the effects of kinin B2 receptor are mediated by intrarenal prostaglandin E2 and nitric oxide generation. The increase in renal interstitial fluid bradykinin during icatibant requires further study of possible alterations in kinin synthesis, degradation, or clearance as a result of B2 receptor blockade.

Comparison of B1 and B2 receptor activation on intracellular calcium, cell proliferation, and extracellular collagen secretion in mesangial cells from normal and diabetic rats

The mesangial cell is a contractile secreting cell found in a key position in the renal glomerulus. Several kidney and systemic diseases are associated with dysfunctions of the mesangial cells. We compared the effect of bradykinin (BK; B2 agonist) and des-Arg9-bradykinin (DBK; B1 agonist) on intracellular calcium mobilization, cell proliferation, and collagen secretion of mesangial cells from normal and streptozotocin-induced diabetic rats. Stimulation of mesangial cells with BK and DBK caused an increase in intracellular calcium (Ca2+). However, the patterns of the Ca2+ increases induced by BK and DBK were different, indicating that DBK induced a major Ca2+ influx, whereas BK preferentially released Ca2+ from intracellular pools. Stimulation with BK and DBK did not show any heterologous desensitization, thus indicating the presence of two distinct binding sites. In normal cells, DBK stimulated cell proliferation more than BK, and this action was potentiated by insulin. No effect of BK or DBK was found in cells harvested from diabetic rats. The proliferation effect of BK and DBK was restored by insulin. DBK stimulated more collagen synthesis than BK in normal cells. In cells harvested from diabetic rats the collagen secretion was increased, but BK and DBK no longer had any effect. Insulin reduced basal collagen secretion in normal cells and cells harvested from diabetic rats. Insulin also blunted stimulation by BK and DBK in normal cells but did not restore the response to BK and DBK in cells harvested from diabetic rats. Our results show that the sensitivity to DBK and BK decreases during the course of insulin-dependent diabetes, indicating modulation by insulin.

The effect of kinin and prostaglandin inhibitors on the renal response to angiotensin-converting enzyme inhibition: a micropuncture study in the dog

It has been suggested that angiotensin-converting enzyme (ACE) inhibition is accompanied by enhanced bradykinin and prostaglandin activities, which may contribute to the renal haemodynamic actions of ACE inhibitors. Therefore we investigated renal function by clearance and micropuncture techniques in dogs maintained either on normal or low-salt diet before and after ACE inhibition with an i.v. bolus of 0.1 mg/kg ramiprilat followed by an infusion of 5 micrograms kg-1 min-1. Subgroups each comprising six dogs were also treated with either HOE-140, a bradykinin B2 receptor antagonist, or the cyclooxygenase inhibitor indomethacin. In general, renal effects of ramiprilat were more pronounced in dogs fed on low salt than in those on normal diet. In dogs on low salt, the mean arterial pressure decreased by 20% 20 min after ramiprilat application, whereas the total renal blood flow rose by 71% from 4.71 to 8.06 ml min-1 g kidney weight-1 and the glomerular filtration rate (GFR) by 28% from 0.74 to 0.95 ml min-1 g-1. Single-nephron glomerular blood flow and single-nephron GFR rose by 55% and 23% respectively. The total and the single-nephron filtration fraction decreased by 25% and 23% respectively. There were no substantial changes in glomerular and peritubular capillary and tubular pressures, but a significant increase in the ultrafiltration coefficient, Kf, by 103% from 3.55 nl/mmHg to 7.19 nl/mmHg (26.7-54.0 nl/kPa) was observed. Afferent and efferent arteriolar resistances decreased in parallel by 55% and 47%.(ABSTRACT TRUNCATED AT 250 WORDS)

Inotropic influence of macrocyclic polyethers on tracheal smooth muscle

Incubated guinea pig tracheal smooth muscle exhibited both positive and negative inotropic responses to a variety of crown ether analogs that ranged in size from 12-crown-4 to 30-crown-10 and included molecules whose lipophilicity was modified by the addition of benzo- and cyclohexo-substituents on the basic molecular framework. The inotropic influence of crown ethers may not only be due to their ionophoretic capabilities but may result from their ability to affect alterations in membrane physiology.

A possible relationship between KCl symport and basolateral K+-conductance in Necturus gallbladder epithelial cells

1. Apical membrane potential (Va), transepithelial potential (VT), fractional apical voltage ratio (FVa = delta Va/delta VT), tissue resistance (RT), and intracellular Cl- (aiCl) and K+ (aiK) activities were measured in isolated gallbladders maintained between oxygenated bicarbonate-free physiological media (23 degrees C, pH 7.2 or 8.2) in a divided chamber. The basolateral membrane potential (Vb) was calculated from the measured values of Va and VT. 2. Cl- removal from the serosal medium (which should accelerate coupled basolateral KCl exit) significantly depolarized Vb, decreased aiCl, decreased FVa, increased RT, and attenuated the depolarization of Vb (delta Vb) induced by high K+ added to the serosal side. These changes are consistent with a decrease in the K(+)-conductance of the basolateral membrane (gbK). 3. Addition of furosemide (an inhibitor of KCl cotransport) to the serosal medium induced significant increases in Vb, FVa, and high K(+)-induced delta Vb, indicating an increase in gbK. 4. In the presence of serosal furosemide, Cl- removal from the serosal medium did not significantly alter Vb, aiCl or delta Vb from their corresponding values when serosal Cl- was present. 5. Serosal furosemide had no significant effect on aiK and aiCl measured with double-barreled ion-selective microelectrodes. 6. These results suggest the possibility of a reciprocal relationship between gbK and the rate of basolateral KCl cotransport. This may contribute to the maintenance of aiK in gallbladder epithelial cells.

Effects of bradykinin on prostaglandin synthesis and cytosolic calcium in rabbit subcultured renal cortical smooth muscle cells

Smooth muscle cells were cultured from an arteriole-rich fraction of the rabbit renal cortex and characterized by their ultrastructural and immunohistochemical features, their high content in creatine kinase (60-times that of the initial preparation) and their ability to synthesize renin. Cells, studied between passages 2 and 5, produced mainly PGE2 and, to a lesser extent, PGF2 alpha. Bradykinin (BK) (0.1 nM-1 microM) induced a concentration-dependent increase in PGE2 (28-40-times basal value at 1 microM after a 5 min incubation period) and stimulated also the free cytosolic calcium concentration [( Ca2+]i) with a 2-fold maximal rise to its basal value. Both effects, inhibited by the anti-B2 receptor [Thi5.8D-Phe7] BK, were not reproduced by DesArg9 BK. A decrease in the extracellular calcium concentration and incubation in the presence of a calcium-channel blocker (lanthanum chloride) inhibited the BK-dependent rise of [Ca2+]i but not that of PGE2. Preincubation with phorbol myristate acetate increased basal and BK-induced PGE2 synthesis but prevented the effect of BK on [Ca2+]i. These results demonstrate the ability of BK to increase [Ca2+]i and PGE2 production in cultured vascular cells from the rabbit renal cortex and suggest that kinins might act on the cortical microcirculation via their direct effects on arteriolar smooth muscle cells.