Kinin-forming enzyme (kininogenin) in homogenates of rat kidney

Subcellular localization of renal kallikrein by ultrastructural immunocytochemistry

The subcellular distribution of immunoreactive kallikrein was described in the rat nephron using ultrastructural immunocytochemistry. The renal tissue was fixed with a mixture of buffered picric acid-paraformaldehyde-glutaraldehyde and immunostained with the peroxidase-antiperoxidase method for the electron microscope with the following steps: antikallikrein antiserum, anti-IgG serum, peroxidase-antiperoxidase complex, 3-3' diaminobenzidine-H2O2, and post-staining with osmium tetroxide. Preabsorption of the primary antiserum with purified rat urinary kallikrein and substitution with normal serum were used as controls. As we have described previously, kallikrein was present exclusively in the connecting tubule cell of the distal nephron. Subcellularly, kallikrein was distributed in luminal membranes, basal membranes, rough endoplasmic reticulum, Golgi apparatus, and vesicles. The immunoreactive vesicles were present in the proximity of the Golgi apparatus and in the cytoplasm in the way between the Golgi and the luminal and basal plasma membranes. No immunostaining was observed in other subcellular components of the connecting tubule cell or in the other type of cell. With the description of kallikrein in subcellular organelles involved in the synthesis, processing, and transport of glycoproteins, we have advanced an hypothetical intracellular processing pathway for renal kallikrein.

Abnormal urinary kallikrein in hypertension is not related to aldosterone or plasma renin activity

The relationships between urinary kallikrein (Ukal), and plasma renin activity (PRA), urinary aldosterone (Ualdo), Na+ balance, SK+, and renal function were studied in essential hypertensives (EHT) and normals. Ukal was measured by a radiochemical esterolytic assay. We studied 18 white patients with EHT (15 men, 3 women) ages 31.6 to +/- 2.1 (SEM) yrs, BP 138 +/- 2/95 +/- 2 mm Hg. and 12 white normals (NLS) (7 men, 5 women) ages 30.2 +/- 2.3 yrs, BP 112 +/- 4/71 +/- 2 mm Hg. All received a 5-day diet of 400 mEq Na+, 80 mEq K+/day, and 5 days of 10 mEq Na+, 80 mEq K+/day. All achieved Na+ balance by Day 5. On Day 5 of the low Na+ diet, 24 hr. Ukal in EHT was 15.8 +/- 2.4 (esterase units/24 hr) vs NLS, 17.0 +/- 2.8 PRA was the same in EHT and NLS, but Ualdo was higher in NLS. (Day 5, low Na+, EHT, Ualdo = 29.4 +/0 3.3 microgram/24h. vs NLS 41.8 +/- 4.7, p less than 0.02). Analysis of individuals showed that all NLS increased Ukal after salt restriction, while 3 EHT decreased Ukal after salt restriction. This abnormal response in EHT was not related to abnormalities in Ualdo, PRA, Na+ balance, SK+, or creatinine clearance. In 3 EHT with low-renin EHT, the Ukal response was normal. In two of four patients with primary aldosteronism, Ukal was normal despite increased Ualdo. The Ukal response to salt restriction is abnormal in some EHT, unrelated to Ualdo or PRA, suggesting either a primary defect in Ukal and/or the presence of other factors modulating Ukal in EHT.

Activation of membrane-bound kallikrein and renin in the kidney

Rat kidney contains membrane-bound renin (EC 3.4.99.19) and kallikrein (EC 3.4.21.8). Kallikrein activity was measured by a spectrophotometric assay and renin by radioimmunoassay. Plasma membrane-bound kallikrein was activated by lysolecithin and by melittin, which was a more potent activator., This activation by mellitin was independent of calcium concentration. Mellitin was, however, a more potent activator of membrane-bound renin in the presence of calcium. Administration of aldosterone to rats for 6 days increased kallikrein activity in the renal homogenate and in the membrane-enriched fractions, whereas renin activity was not affected. It was proposed that kallikrein may also be located on the basal membrane of tubular epithelial cells, where aldosterone can enhance its activity.

Kininogenase activity in plasma membranes and cell organelles from rabbit kidney cortex: subcellular localization of renal kallikrein by free-flow electrophoresis and density-gradient fractionation

Subcellular fractions were prepared from a rabbit kidney cortex homogenate by density gradient and free-flow electrophoresis techniques. After enzymatic and morphologic characterization, we determined the kininogenase activity in the different fractions. This activity was present in those plasma membranes that also contained high specific activities Na-K-ATPase and in lysosomal-like particles. No activity was found in the lumen, that is, the microvillous part of the proximal tubule cell. The kallikrein-like nature of this kininogenase activity was established by several methods.

Synthesis of kallikreins by rat kidney slices

1 Four radioactive akllikreins were isolated from rat kidney slices incubated with (3H)-L-leucine. 2 The kallikreins were purified by procedures previously used for the isolation of rat urinary kallikreins (Nustad & Pierce, 1974), and by affinity chromatography on a column of insolubilized anti-rat urinary kallikrein. 3 The kidney kallikreins resembled the urinary kallikreins in their relative amounts, isoelectric points and electrophoretic mobilities on polyacrylamide disc gels. 4 The data indicate that the kidney synthesizes four kallikreins which are released into urine. The kallikreins are not changed by passage through the lower urinary tract.

Subcellular localization of renin and kininogenase in the rat kidney

1. The distribution of enzymatic activities was determined in subcellular fractions of rat kidney cortex homogenates after various homogenization procedures. The specific activities of kininogenase (KGA), BAEE esterase (pH 8.5), alkaline phosphatase and glucose-6-phosphatase were, on average, 3.4 times higher in the microsomal fraction than in the whole homogenate. The total amount of these activities in the microsomal fraction after gentle, ordinary and forced homogenization were about 15, 40 and 65% of total recovered activities, respectively. These results confirmed the localization of KGA in the microsomal fraction.2. Renin activity was primarily recovered in the heavy mitochondrial fraction. When the force of the homogenization was increased some renin activity was shifted to the soluble fraction.3. When a mixture of renin and purified urinary KGA was given intravenously to an anaesthetized rat, a hypotensive response due to the KGA was followed by a hypertensive renin response. Over a certain range of concentrations KGA and renin could be measured simultaneously. In fractions of kidney homogenates, however, KGA activity was too low to be measured by this method.

The relationship between kidney and urinary kininogenase

1. Rat kidneys which were perfused with saline contained both kininogenase (KGA) and kininase activity. These activities were separated by gel filtration on a Sephadex G-100 column. The kininase activity was excluded from the column whereas the KGA activity was retained. Kidney KGA activity was primarily found in the sedimentable fraction of the homogenate.2. The kidney KGA activity was compared with the urinary KGA activity, and the following properties were found to be the same: molecular dimension, pH optimum, effect of inhibitors, and ability to liberate kinins from kininogens.3. A urinary sample collected over 24 h contained about 8 times the KGA activity found in the corresponding kidneys at the end of the collection period. The urine: kidney ratio for alkaline phosphatase was about 0.01.4. The ability of kidney and urinary samples to hydrolyse N-alpha-benzoyl-L-arginine ethyl ester (BAEE) at pH 8.5 paralleled the KGA activity.

Localization of kininogenase in the rat kidney

1. The rat kidney kininogenase (KGA) activity was located mainly in the kidney cortex.2. Differential centrifugation of kidney cortex homogenate revealed that the microsomal fraction contained more KGA activity per unit of protein than the other subcellular fractions.3. Subfractionation of the microsomal fraction showed that the KGA activity was recovered in a subfraction also containing high specific activity of both alkaline phosphate and glucose-6-phosphatase. It is suggested that the KGA activity is localized in the plasma membrane and/or endoplasmic reticulum membranes of kidney cortical cells.4. Hydrolysis of N-alpha-benzoyl-L-arginine ethyl ester at pH 8.5 paralleled the KGA activity.

Renal erythropoietic factor: role of ions and vasoactive agents in erythropoietin formation

Evidence is provided for the existence of a renal erythropoietic factor, devoid of vasopressor activity, which upon interaction in vitro with normal serum yields erythropoietin. When undialyzed serum is used, erythropoietin inactivation develops in the incubation mixtures, and this inactivation appears to be dependent on an enzymatic component in preparations of the factor and on ions in serum.