Renal impairment in chronic cigarette smokers

To determine the effect of chronic cigarette smoking on renal function, a cross-sectional study was carried out with 30 subjects who had no known vascular disease risk factor other than cigarette smoking, and 24 age- and sex-matched controls without any vascular risk factor including cigarette smoking. Renal function by radionuclide studies of renal plasma flow, GFR, and plasma endothelin-1 concentration was determined. Compared with nonsmokers, smokers had a renal function impairment characterized by a normal GFR and a significant reduction in renal plasma flow as reflected by MAG3 clearance (199.20 +/- 58.85 ml/min per 1.73 m2 versus 256.54 +/- 60.14 ml/min per 1.73 m2; t = 3.52, P < 0.001). MAG3 clearance was significantly correlated with age and smoking. The renal dysfunction was associated with an increase in plasma endothelin-1 concentration (21.56 +/- 1.15 pmol/L versus 25.01 +/- 3.21 pmol/L; t = 5.00, P < 0.001). Former smokers as well had similar, although milder, abnormalities. In conclusion, cigarette smokers manifest an impairment of renal function, suggesting that smoke may have a detrimental effect on renal function.

Pathogenesis of idiopathic calcium nephrolithiasis: update 1997

Idiopathic calcium nephrolithiasis (ICN) is a frequent disease in Western countries. The physicochemical theory of lithogenesis, which explains stone formation by the precipitation, growth, and crystalline aggregation of lithogenic salts in the urine, has contributed greatly to the understanding of the pathogenesis of calcium urolithiasis. However, several aspects are still unexplained; the co-existence of familial occurrence, primary tubular dysfunctions with ICN, and anomalies in the systemic handling of oxalate and calcium led to the development of a cellular hypothesis of ICN. A number of cellular defects in the handling of ions has been reported that involves both anion and cation transport. These anomalies are probably the expression of a still unknown cellular defect in idiopathic calcium stone formers. We suggested that an anomaly in the cell membrane composition might be responsible for the complex array of cell ion flux abnormalities observed in ICN. Recently, a disorder in the n-6 polyunsaturated fatty acid series has been described; it is characterized by a lower linoleic acid content and a higher arachidonic acid concentration in both plasma and erythrocyte membrane phospholipids of renal calcium stone patients. This anomaly could cause an increased activity of ion carriers; furthermore, it may lead to increased prostaglandin synthesis and to secondary phenomena at the kidney, skeletal, and intestinal level. As a consequence, critical conditions for lithogenesis in the kidney may ensue. The data suggest a common pathogenesis for hypercalciuria and hyperoxaluria. The systemic defect in the phospholipid arachidonic acid level may be both of dietary or genetic origin; experimental data suggest that the increase in delta-6 desaturase activity, the limiting enzyme in the metabolic pathway of polyunsaturated fatty acids, might be relevant to the pathogenesis of lipid abnormalities observed in nephrolithiasis and to the pathogenesis of ICN and its related problems (at the kidney, intestinal, and bone level).

Growth factors and the kidney in diabetes mellitus

Nephromegaly and mesangial matrix expansion observed in the diabetic kidney are all clues of a role of growth factors in the pathogenesis of these lesions. A growing body of evidence shows that changes in (1) insulin-like growth factor I regulation, and (2) the transforming growth factor beta loop exist in the kidney in the diabetic hypertrophic kidney and in diabetic glomerulosclerosis. However, other growth factors may be involved in some diabetic renal changes. The abnormalities in growth factor content and regulation, the role of growth factors in the diabetic kidney, and the effect of hyperglycemia and advanced glycosylation end products on growth factors in the kidney are reviewed.

Intracellular processing of transforming growth factor-beta in mesangial cells

Transforming growth factor beta 1 (TGF-beta 1) is a multifunctional regulator of cell-growth, differentiation and extracellular matrix formation in several physiological conditions. It plays a crucial role in the process of glomerulosclerosis. Mature TGF-beta 1 is secreted as a latent form associated with the latency associated peptide (LAP), and its activation occurs through the LAP cleavage. The intracellular localization and the mechanisms of activation of TGF-beta 1 protein have not been elucidated in the mesangial cell. In the present report we examined the intracellular processing from TGF-beta 1 precursor to the latent-TGF-beta 1 in cultured mesangial cells by immunocytochemistry, using three rabbit polyclonal antibodies directed against different epitopes of human TGF-beta 1. The anti-LAP-TGF-beta 1 precursor Ab stained mesangial cells in the perinuclear region and in the cytoplasm in the area corresponding to the rough endoplasmic reticulum; the anti-COOH-terminal fragment of TGF-beta 1 Ab reacted in the same area, in vesicular structures located in the cytoplasm and furthermore, in the mesangial cell clusters, so-called hillocks, with an extracellular pattern; the anti-NH2-terminal fragment of TGF-beta 1 Ab stained only large exocytotic vesicles at the periphery of the cytoplasma. Our investigations suggest a conformational rearrangement of pro-TGF-beta 1 molecule occurring between the rough endoplasmic reticulum and the TGF-beta 1 secretion and support the idea that in mesangial cells the activation of TGF-beta 1 occurs during the secretion process. In conclusion, the processing of TGF-beta 1 in mesangial cells seems to be similar to that one observed in other mesenchymal cells.

Heparin and diabetic nephropathy

The following is an abstract of the article discussed in the subsequent letter:

Marshall, Sally M., Klavs W. Hansen, Ruth Østerby, Jan Frystyk, Hans Ørskov, and Allan Flyvbjerg. Effects of heparin on renal morphology and albuminuria in experimental diabetes. Am. J. Physiol. 271 ( Endocrinol. Metab. 34): E326–E332, 1996.—Female nondiabetic and streptozotocin diabetic Wistar rats received 200 units heparin two times daily by subcutaneous injection for 6 mo. Mesangial volume fraction was reduced in heparin-treated control (CH) compared with untreated control (C) animals (CH 0.18 ± 0.02 vs. C 0.24 ± 0.02, P < 0.05), but other histological parameters were similar. In the heparin-treated diabetic (DH) group, wet kidney weight was increased compared with the untreated diabetic (D) group (DH 1,156 ± 39 vs. D 1,050 ± 30 mg, P < 0.05), as were absolute, but not fractional, glomerular volume ( P < 0.05) and capillary volume ( P < 0.05). Basement membrane thickness (DH 193 ± 3 vs. D 231 ± 9 nm, P < 0.01) and mesangial/glomerular volume fraction ( P < 0.001) were decreased. Urinary albumin excretion was increased in the heparin-treated control animals compared with control animals [CH 980 (range 150–4,446) vs. C 221 (range 86–654) μg/24 h, P < 0.001] and in the heparin-treated diabetic animals compared with the diabetic animals [DH 12,785 (range 4,495–29,520) vs. D 899 (range 450–1,335) μg/24 h, P < 0.001]. Thus the possibly deleterious increases in glomerular capillary volume and albumin excretion may negate the beneficial effects of heparin on mesangial and basement membrane structures.

Down-regulation of glomerular matrix metalloproteinase-2 gene in human NIDDM

Regulation of mesangial matrix deposition is a dynamic phenomenon involving synthetic and degradative processes. The latter involve a number of matrix metalloproteinases (MMP) and tissue inhibitors of matrix metalloproteinases (TIMP). Experimental studies suggest that mesangial matrix degradation is inhibited in diabetic nephropathy, and that this phenomenon has a pathogenic role. The expression of genes for MMP2 and TIMP2 in human diabetic nephropathy was investigated. Reverse transcription polymerase chain reaction was carried out in microdissected glomeruli and tubulo-interstitium obtained from kidney biopsies. We studied 16 NIDDM patients, 5 patients with glomerulonephritis or chronic kidney transplant rejection, and 5 normal control subjects. Albumin excretion rate and renal histology for NIDDM patients were available. Contrary to TIMP2 which was expressed both in tubulo-interstitium and glomeruli in almost all renal biopsies, MMP2 gene down-regulation was observed in glomeruli from all NIDDM patients, irrespective of the albumin excretion rate, and of renal histology. In contrast, this gene was expressed in biopsies from other subjects (chi(2) = 20.6; p = 0.000). In conclusion, this study demonstrates that: 1) in glomeruli of NIDDM patients the MMP2 gene is down-regulated; 2) in biopsies of NIDDM patients the MMP2/TIMP2 pattern is peculiar for NIDDM; 3) the MMP2 gene down-regulation is observed in all NIDDM patients, irrespective of the level of albuminuria and of renal histology. MMP2 gene down-regulation seems to be a molecular epiphenomenon of diabetes, rather than a marker of diabetic nephropathy.

Attenuation of aspirin-induced bronchoconstriction by sodium cromoglycate and nedocromil sodium

The protective activity of nedocromil sodium and of sodium cromoglycate against aspirin-induced asthma has never been investigated in controlled studies. Because it has been reported that aspirin-induced platelet-mediated cytotoxic activity in vitro is inhibited after treatment in vivo with nedocromil but not with cromoglycate, we investigated whether these compounds also exhibit a different protective activity against aspirin-induced bronchoconstriction. Ten patients with aspirin-induced asthma underwent three bronchial challenges with a single dose of lysine acetylsalicylate (LASA) that caused a decrease in FEV1 of 25% or more in a preliminary dose-response test 30 min after inhalation of 4 mg nedocromil sodium, 10 mg sodium cromoglycate, or placebo. FEV1 and SRaw were recorded at intervals for 195 min. After placebo, LASA caused a maximal decrease in FEV1 of 42 +/- 4% of baseline. After cromoglycate and nedocromil the maximal decrease in FEV1 was reduced to 20 +/- 3% and 18 +/- 4%, respectively (p < 0.01 versus placebo for both treatments), without significant differences between the two treatments. Similar results were observed with SRaw. We conclude that, at the recommended therapeutic doses, sodium cromoglycate and nedocromil sodium are equally effective in attenuating aspirin-induced bronchoconstriction and that it is unlikely that platelet activation participates in the pathogenesis of aspirin-induced asthma.

Von Willebrand factor abnormalities in IgA nephropathy

BACKGROUND

Plasma concentration of von Willebrand factor (vWF) has been used as an index of endothelial dysfunction. Increased release of vWF from endothelial cells has been reported in several conditions, and there is also evidence that dysfunctioning endothelial cells synthesize defective molecules. In fact, unusually large vWF multimers have been described and related to the pathogenesis of some microangiopathic diseases. Abnormal levels of vWF have been reported in primary glomerulitis, but this was no referred to histological diagnosis. Furthermore, no qualitative vWF analysis was performed in these glomerulopathies. Therefore the aim of our study was to analyse quantitatively and qualitatively vWF in patients with IgA (IgAN) and non-IgA mesangial proliferative glomerulonephritis (PGN).

METHODS

Fourteen IgAN patients, eight PGN patients, seven subjects with different glomerulonephritides, and 10 healthy controls formed the basis of this study. On peripheral venous blood collected in the presence of protease inhibitors, vWF parameters were investigated. vWF antigenic activity (vWF:Ag) was measured by electroimmunodiffusion. vWF subunits mobility was studied by crossed immunoelectrophoresis (CIE) and in some patients vWF multimeric analysis was performed by SDS-agarose gel electrophoresis.

RESULTS

Mean vWF:Ag was significantly higher in PGN patients as compared to controls, while there was no significant difference between PGN and IgAN patients and between IgAN and controls. CIE revealed a pre-peak in 12 of 14 IgAN patients and a migration index which did not differ between controls, IgAN, and PGN subjects. No pre-peak was observed in PGN and in other glomerulonephritides. Analysis of plasma vWF multimeric pattern by SDS-agarose gel electrophoresis disclosed in four IgAN patients abnormally large vWF multimers that were not documented in PGN subjects.

CONCLUSIONS

This study, by showing the presence of a pre-peak and of large vWF multimers in IgAN patients, suggests an altered postsecretory handling of the vWF in IgAN and possibly a different role of the vWF in IgAN in respect to PGN.

Effect of glucose and heparin on mesangial alpha 1(IV)COLL and MMP-2/TIMP-2 mRNA expression

Mesangial cells are responsible for the synthesis of mesangial matrix as well as its degradation, which is mediated by a number of proteolytic activities, including metalloproteinases (MMPs). Imbalanced matrix protein metabolism may be responsible for mesangial expansion and glomerulosclerosis in diabetic nephropathy. Heparin prevents this complication. In human and murine mesangial cell cultures, RT-PCR was able to detect mRNA expression for a number of molecules involved in the mesangial extracellular matrix turnover: type IV collagen [alpha 1(IV)COLL], MMP-1, MMP-2, MMP-3, MMP-9 and MMP-10, and the tissue inhibitors TIMP-1 and TIMP-2. The expression of mRNA for alpha 1(IV)COLL and MMP-2/TIMP-2 balance was studied in human cells in the presence of high glucose and heparin. mRNAs for all the studied molecules were expressed at different levels. Interestingly, a shift in the balance of alpha 1(IV)COLL, MMP-2 and TIMP-2 was observed in high glucose, which was partially reversed by heparin supplementation. The new equilibrium was mostly due to the down-regulation of type IV collagen expression, rather than further reduction of potential proteolysis. Our data, while extending the list of potential mediators of mesangial matrix catabolism, highlight a molecular mechanism by which the pathogenesis of diabetic nephropathy may be sustained, and at the same time suggest that heparin may have the potential to correct this abnormality.

Anomalous phospholipid n-6 polyunsaturated fatty acid composition in idiopathic calcium nephrolithiasis

Anomalies in the erythrocyte transport of anions and cations have been described in idiopathic calcium oxalate nephrolithiasis and seem to play a pathogenetic role in this disease. In consideration of the hypothesis that the complex array of ion flux cell abnormalities is an epiphenomenon of an anomaly in the composition of cell membranes, this study investigated cell-membrane lipid composition. In idiopathic calcium oxalate renal stone formers, in which ion transport abnormalities were present, and in healthy control subjects, plasma and erythrocyte membrane lipid composition, the erythrocyte oxalate exchange, and Na/K/2Cl cotransport activity were evaluated. Furthermore, in stone formers, the effect of a 30-day fish-oil diet supplementation on plasma lipids, erythrocyte oxalate exchange, oxaluria, and calciuria was investigated. The effect of archidonic acid released by phospholipase A2 on anion-carrier phosphorylation and activity in erythrocytes was evaluated as well. Patients had a lower content of linoleic and higher concentration of archidonic acids in both plasma and erythrocyte membrane phospholipids, and an increased archidonic/linoleic acid ratio. The archidonic acid level correlated with the erythrocyte oxalate exchange and sodium cotransport activity. Fish-oil supplementation lowered calcium and oxalate urine excretion, and normalized the erythrocyte oxalate exchange. Phospholipase A2 increased the erythrocyte anion-carrier protein phosphorylation and the oxalate exchange. This study shows that idiopathic calcium nephrolithiasis in the patient group reported here is characterized by a systemic defect in phospholipid archidonic acid levels that might provide an answer to the link between genetic background, dietary habits, and renal lithiasis.

The abnormal red-cell oxalate transport is a risk factor for idiopathic calcium nephrolithiasis: a prospective study

An abnormal erythrocyte transmembrane oxalate flux was described in recurrent idiopathic calcium nephrolithiasis. To verify whether it might represent a risk marker of renal stone disease, two prospective studies were carried out. One hundred ninety patients with idiopathic calcium nephrolithiasis who were enrolled at their first episode of lithiasis during the period 1984 to 1986, form the basis of the first prospective study. The impact of erythrocyte oxalate transport anomaly, gender, familial occurrence of nephrolithiasis, hypercalciuria, hyperoxaluria, and hyperuricosuria on stone recurrence by both bivariate and multivariate analysis of frequencies was assessed. The predictive value of the erythrocyte anomaly for a patient's becoming a stone former was also assessed in five nephrolithiasis families. Recurrence occurred in 57.9% of patients; this was significantly associated with the erythrocyte anomaly, hyperoxaluria, and male gender. However, when using multivariate analysis, only gender and the erythrocyte anomaly were statistically significant and were independent predictors of recurrency. The probability of stone recurrency predicted by the logistic model ranged from 30.1% for women with normal erythrocyte oxalate transport, to 73.4% for men with the erythrocyte anomaly. The family follow-up showed that only subjects with the erythrocyte abnormality become renal stone-formers in the 8-yr survey. By showing the predictive value of the erythrocyte oxalate anomaly for recurrent calcium nephrolithiasis, our findings support the notion that this anomaly is a risk factor in renal stone disease.

Increased glomerular alpha 1 (IV) collagen expression and deposition in long-term diabetic rats is prevented by chronic glycosaminoglycan treatment

Diabetic nephropathy is associated with thickening of the glomerular basement membrane and, in particular, with mesangial matrix expansion. Previous studies have indicated that administration of chemically modified, low-anticoagulant heparins prevents some of the morphologic and physiologic alterations occurring in experimental diabetic nephropathy. The effect of prolonged heparin treatment on the glomerular expression and deposition of alpha 1 (IV) collagen, which is a major component of the mesangial matrix, has not been reported previously. Four groups of rats were studied for 12 months: two control groups and two groups of streptozotocin-diabetic rats. One group in each branch received modified heparin continuously from the induction of diabetes. After 12 months synthesis and deposition of alpha 1 (IV) collagglomerula and adjacent tubuli were determined by nonradioactive in situ hybridization and immunohistochemistry. Mesangial cells were localized by Thy 1.1 staining. Long-term diabetes caused a significant increase in alpha 1 (IV) collagen deposition in the mesangial matrix and a more than 2-fold enhancement of glomerular cell alpha 1 (IV) collagen transcript levels, mainly in mesangial cells. The alpha 1 (IV) collagen mRNA levels of proximal tubular cells and visceral epithelial cells were similarly increased. Chronic treatment of diabetic rats with modified heparin completely prevented the increased alpha 1 (IV) collagen deposition and expression. The increased glomerular deposition of alpha 1 (IV) collagen observed in long-term streptozotocin diabetic rats appears to depend on an increased alpha 1 (IV) collagen synthesis. Because chronic application of low-anticoagulant heparin completely prevents the increased alpha 1 (IV) collagen synthesis by mesangial cells, this result suggests a new therapeutic option for the prevention of diabetic nephropathy in humans.

Inhaled PGE2 prevents aspirin-induced bronchoconstriction and urinary LTE4 excretion in aspirin-sensitive asthma

Bronchial overproduction of leukotrienes and inhibition of prostaglandin synthesis are involved in the pathogenesis of aspirin-induced asthma. We investigated whether inhaled prostaglandin E2 (PGE2) attenuates the response to bronchial challenge with lysine acetylsalicylate (LASA) and the associated increase in urinary leukotriene E4 (u-LTE4) in seven aspirin-sensitive subjects with asthma. Each subject performed two challenges with a single dose of LASA that caused a decrease in FEV1 of 20% or more in a preliminary test, immediately after inhaling 100 micrograms PGE2 in 4 ml saline or placebo, according to a randomized double-blind protocol. FEV1 was recorded at 30-min intervals for 4 h. u-LTE4 was measured by combined high-performance liquid chromatography enzyme immunoassay at 2-h intervals. After placebo, LASA caused an obstructive reaction in all patients, with a maximum decrease in FEV1 of 35 +/- 5% with respect to baseline. u-LTE4 rose from 911 +/- 261 picograms (pg)/mg creatinine at baseline to a maximum value of 2249 +/- 748 after challenge. Inhaled PGE2 provided almost complete protection in all patients. Baseline u-LTE4 was 883 +/- 243 pg/mg creatinine and did not change significantly during the test, reaching a maximum value of 864 +/- 290 (p < 0.05 versus placebo). These results confirm that PGE2 is highly effective in preventing aspirin-induced asthma and suggest that this effect is mediated by inhibition of sulfidopeptide leukotriene production.

Erythrocyte transmembrane flux and renal clearance of oxalate in idiopathic calcium nephrolithiasis

An anomaly in erythrocyte oxalate transport has been reported in patients with idiopathic calcium oxalate nephrolithiasis. Even if clinical and experimental evidence suggests a causal role of this cellular anomaly in calcium nephrolithiasis, a definitive answer to this fundamental question is still lacking. We approached this problem by searching for a possible relationship between the erythrocyte oxalate self-exchange anomaly and the renal clearance of this anion in stone formers. In 10 idiopathic calcium-oxalate renal stone formers, and 10 healthy subjects we evaluated the erythrocyte oxalate flux rate, and the renal fractional clearance of oxalate by a recently described enzymathic procedures for plasma oxalate determination. With respect to controls, stone formers had higher oxalate flux rate in erythrocytes, and higher oxalate renal fractional clearance with a significant direct correlation between the two parameters. These data are compatible with a membrane transport abnormality within the kidney of these stone formers, and the existence of a common defect of the oxalate transport shared by both erythrocytes and tubular renal cells. The latter may be crucial in the pathogenesis of calcium oxalate nephrolithiasis, by modifying the renal handling of oxalate.

Use of glycosaminoglycans to increase efficiency of long-term continuous peritoneal dialysis

Long-term continuous ambulatory peritoneal dialysis (CAPD) frequently induces progressive structural changes in the peritoneal membrane, leading to dialysis failure. Because heparin and glycosaminoglycans favourably remodel anatomical barriers exposed to injury, we studied the effect of intraperitoneal administration of glycosaminoglycans on peritoneal dialysis efficiency. 16 CAPD patients received glycosaminoglycans for 30 days followed by a 30-day wash-out. Glycosaminoglycans in urea and creatinine dialysate-to-plasma ratios significantly increased (means 0.86 and 0.78 at baseline, 0.92 and 0.82 at 30 days, respectively). Peritoneal protein loss was reduced, and serum albumin concentration increased. We now need to assess whether glycosaminoglycans can postpone dialysis failure in the long term.

Time-limited protective effect of inhaled frusemide against aspirin-induced bronchoconstriction in aspirin-sensitive asthmatics

Inhaled frusemide effectively prevents the bronchial obstructive response to allergens and to a number of nonallergic stimuli. In most of the experimental models in which it has been tested, the protective effect of frusemide has been evaluated for only a short time after administration. In aspirin-sensitive patients, acetylsalicylic acid causes an asthmatic reaction which typically lasts for 2 h or more after exposure. We investigated the presence and duration of the protective effect of inhaled frusemide against the bronchial response to aspirin in sensitive patients, using a specific inhalation challenge with lysine acetylsalicylate (LASA). In the first study, eight subjects with aspirin-asthma underwent two bronchial challenges with a single dose of lysine acetylsalicylate administered through a jet nebulizer, after treatment with 40 mg inhaled frusemide or placebo, according to a randomized, double-blind protocol. Forced expiratory volume in one second (FEV1) was monitored for 120 min after challenge. In the second study in eight patients, the protocol was modified by the use of a dosimeter for delivery of lysine acetylsalicylate, by reducing the dose of lysine acetylsalicylate to avoid intense reactions, and by extending the follow-up to 4 h. In the first study, after placebo, FEV1 gradually decreased, reaching a maximum decrement of 39 +/- 3% at 120min. Inhaled frusemide exerted a significant protection at all time-points, although this activity appeared to decrease with time. In the second study, after placebo, inhaled lysine acetylsalicylate caused a gradual decrease in FEV1, which reached a maximum decrement at 180 min.(ABSTRACT TRUNCATED AT 250 WORDS)

Treatment with a glycosaminoglycan formulation ameliorates experimental diabetic nephropathy

Previous studies have indicated that administration of glycosaminoglycans can prevent some of the morphological and physiological alterations which occur in experimental diabetic nephropathy. The aims of this study were to further elucidate the effect of these drugs on glomerular basement membrane permeability by dextran clearance studies, to test the ability of glycosaminoglycans to revert established diabetic nephropathy and to examine the effect of glycosaminoglycans on renal extracellular matrix synthesis. Five groups of Sprague-Dawley rats were studied for 12 months: two control groups (treated or untreated non-diabetic), three streptozotocin diabetic animal groups, two of which received a glycosaminoglycan formulation, one from the induction of diabetes and the other after the fifth month of diabetes. At five months the 35S-sulfate glomerular incorporation, albuminuria, glomerular basement membrane thickness and anionic charge density were determined. At 12 months albuminuria, renal collagen IV and perlecan mRNA levels, anionic and neutral dextran clearances, glomerular basement membrane morphometry, and mesangial cell proliferation were evaluated. We demonstrate that long-term administration of glycosaminoglycans prevents renal morphological and functional alterations in diabetic rats and appears to revert established diabetic renal lesions. Glycosaminoglycan administration modified renal matrix composition by the normalization of collagen gene expression and increasing glomerular 35S-sulfate incorporation.

Relationship between membrane protein phosphorylation and intracellular translocation of casein kinase in human erythrocytes

The present paper shows that an increased phosphorylation of the membrane proteins, promoted by the okadaic acid (strong inhibitor of P-Ser/Thr-protein phosphatase(s)), is accompanied by a release of casein kinase from the membrane into cytosol. Such an intracellular translocation might provide a feedback mechanism for the regulation of the casein kinase catalyzed phosphorylation of membrane proteins in the human erythrocytes.