Toshihiro Okuda

Involvement of rho in GTPγS-induced enhancement of phosphorylation of 20 kDa myosin light chain in vascular smooth muscle cells: inhibition of phosphatase activity

In β‐escin‐permeabilized cultured pig aortic smooth muscle cells GTPγS dose‐dependently enhances Ca2+‐induced wortmannin‐sensitive phosphorylation of 20 kDa myosin light chain (MLC20). GTPγS does not potentiate thiophosphorylation of MLC20, but does inhibit its dephosphorylation. Pretreatment with C. botulinum exotoxin C3, which specifically ADP‐ribosylates and inactivates the rho family of the small molecular weight G proteins, completely abolishes the effects of GTPγS. These results indicate that rho is involved in the GTPγS‐induced enhancement of Ca2+‐dependent MLC20 phosphorylation in aortic smooth muscle cells, and strongly suggest that this effect of rho is due to inhibition of protein phosphatase activity toward MLC20.

Angiotensin II and vasopressin stimulate calcium-activated chloride conductance in rat mesangial cells.

In an attempt to clarify the mechanisms by which angiotensin II (AII) and arginine vasopressin (AVP) regulate mesangial cell function, we examined the membrane potential change of mesangial cells and found that cells contracted and membrane potential depolarized in response to AII and AVP. The depolarization was associated with decreased input resistance. Ca ionophore A23187 caused similar mesangial cell contraction and depolarization. The reversal potential (Vr) of the depolarization response to AII and AVP was -29 +/- 3 and -25 +/- 7 mV (mean +/- SD), respectively. Not only the Vr of the AII-induced depolarization but also Vr of the Ca ionophore-induced response was dependent upon the extracellular Cl- concentration. Further, AII and AVP caused cell contraction and membrane depolarization in Ca++-free medium containing 0.5 mM EGTA. These data suggest the presence of Ca++ -activated Cl- channels in the mesangial cells and that AII and AVP increase Cl- permeability via an elevation of [Ca++]i released from the intracellular organellae.

Ambient C1- ions modify rat mesangial cell contraction by modulating cell inositol trisphosphate and Ca2+ via enhanced prostaglandin E2.

Our recent observation showed that angiotensin II (AII) and arginine vasopressin (AVP) stimulate Ca2+-activated Cl- conductance in mesangial cells. These data raise the possibility that mesangial cell function may be modulated by extracellular chloride concentration [( Cl-]o). The present study was undertaken to test this possibility using cultured rat mesangial cells. When the [Cl-]o was reduced to zero, the percentage of mesangial cells showing contraction responding to AII and AVP was decreased from 72 +/- 9 to 33 +/- 10% and from 60 +/- 4 to 24 +/- 11%, respectively. Ca2+ transients induced by AII and AVP, measured in mesangial cells loaded with Ca2+-sensitive photoprotein aequorin, were attenuated as [Cl-]o decreased. Also, when [Cl-]o decreased, inositol trisphosphate (IP3) levels of mesangial cells were suppressed, both in the presence and absence of AII or AVP. PGE2 production by mesangial cells increased when [Cl-]o decreased and the effects of ambient Cl- deprivation could be restored by addition of indomethacin to the Cl- -free medium. Moreover, PGE2 decreased mesangial cell contractility, Ca2+ transients, and IP3 production in response to AII and AVP. These data suggest that the decrease in [Cl-]o attenuates mesangial cell contraction by suppressing IP3 production and thus Ca2+ transients in response to AII and AVP through enhanced PGE2 production.

Mesangial cell ion transport and tubuloglomerular feedback.

Mesangial cells possess Ca(2+)-activated Cl- channels, Ca(2+)-activated K+ channels, voltage-gated Ca2+ channels, ATP-sensitive K+ channels, and two types of nonselective cation channels. Angiotensin II and arginine vasopressin depolarize the membrane. This membrane depolarization is caused by the activation of Ca(2+)-activated Cl- and Ca(2+)-activated nonselective cation channels through an elevation of intracellular Ca2+ concentration. The Ca(2+)-independent nonselective cation channel is activated by platelet-derived growth factor and is a candidate for the receptor-activated Ca2+ influx system. It has been suggested that macula densa Cl- reabsorption determines the Cl- concentration of juxtaglomerular apparatus interstitial fluid and thereby affects the resistance of afferent arterioles. In addition, angiotensin II-mediated and arginine vasopressin-mediated mesangial cell Ca2+ signals and contraction are attenuated via prostaglandin production by the mesangial cells themselves when the ambient Cl- concentration is reduced. Thus, Cl- plays an essential role in the tubuloglomerular feedback mechanism. The intracellular Ca2+ concentration appears to be important for the signal transduction mechanism of tubuloglomerular feedback. The ionic channels on the mesangial cell membrane may participate in controlling the intracellular Ca2+ concentration. The association of disturbed tubuloglomerular feedback and the development of hypertension has recently been reported.

Breastfeeding and prevalence of allergic diseases in Japanese university students

BACKGROUND Although historical support exists for the concept that breastfeeding might be protective against allergic diseases, contradictory findings have been observed recently. OBJECTIVE To investigate the cumulative prevalence of allergic diseases in Japanese university students and to identify explanatory variables including breastfeeding. METHODS From March 18, 2003, through March 29, 2005, a total of 9,615 students newly enrolled at the University of Tokyo responded to a written questionnaire on allergic diseases. RESULTS Cumulative prevalence of allergic rhinitis, atopic dermatitis, and asthma was 47.2%, 17.4%, and 9.3%, respectively. These data were closely correlated, and prevalence of any 1 of the 3 diseases significantly increased the odds for historical prevalence of the other 2 (P < .001). Male sex (odds ratio [OR], 1.5; 95% confidence interval [CI], 1.4-1.7) and maternal (OR, 2.2; 95% CI, 2.0-2.5) or paternal (OR, 1.6; 95% CI, 1.4-1.8) history of allergic rhinitis were significant correlates of increased odds for allergic rhinitis. Maternal (OR, 2.7; 95% CI, 1.6-4.5), paternal (OR, 3.8; 95% CI, 2.2-6.6), or sibling (OR, 1.9; 95% CI, 1.5-2.4) history of atopic dermatitis was a significant correlate of increased odds for atopic dermatitis. As for asthma, maternal (OR, 4.9; 95% CI, 3.0-7.9), paternal (OR, 4.0; 95% CI, 2.3-7.0), or sibling (OR, 3.3; 95% CI, 2.4-4.5) history of asthma was a significant correlate of increased odds. Logistic regression analysis showed no consistent evidence of the effects of breastfeeding on the cumulative prevalence. CONCLUSION The cumulative prevalence of these diseases among young adults revealed that the effect of breastfeeding is negligible when compared with genetic factors.

Angiotensin II Enhances Glomerular Expression of a Nonmuscle Myosin Heavy Chain, SMemb, with Extracellular Matrix Accumulation

Background/Aims: We previously showed that the mesangial expression of nonmuscle-type myosin heavy chain, SMemb, was related to glomerular sclerosis. Although angiotensin II (AII) is known to promote the glomerular accumulation of extracellular matrix and sclerosis, the effect of AII on the mesangial expression of SMemb is unknown. Thus, we investigated the effect of AII on the mesangial expression of SMemb and synthesis of fibronectin. Methods: We continuously administered AII to Sprague-Dawley rats with subcutaneous osmotic minipumps for 14 days. Control animals received normal saline instead. The effects of oral administration of an AII type 1 (AT1) receptor antagonist, candesartan cilexetil, and a vasodilator, hydralazine, were also examined. Results: Semiquantitative immunohistochemical evaluation and Western blot analysis showed that AII significantly enhanced glomerular expression of SMemb (0.87 ± 0.33 vs. 0.40 ± 0.19 for immunohistochemical grading, p < 0.05; 2.55 ± 0.88 vs. 1.16 ± 0.75 for Western blot analysis, p < 0.05). Glomerular fibronectin was also increased in AII-administered rats (301.7 ± 206.8 ng/5 µg protein vs. 95.8 ± 81.3 ng/5 µg protein, p < 0.05). Candesartan cilexetil attenuated these effects. On the other hand, hydralazine did not change the glomerular expression of SMemb enhanced by AII administration. Conclusion: All induced a phenotypic alteration in mesangial cells, enhanced the mesangial expression of SMemb and stimulated the fibronectin synthesis. These results suggest that the mesangial expression of SMemb is related to glomerular matrix accumulation and that AII mediates both mesangial processes via AT1 receptors.

Modification of mesangial cell function by ambient chloride is absent in Dahl salt sensitive rat

Summary: We previously reported that the normally present modification of mesangial cell function by ambient chloride concentration ([Cl]) and insulin was lacking in mesangial cells obtained from spontaneously hypertensive rats (SHR). This aberrant modification of the mesangial cell might be related to the development of hypertension. In this study, we examined if a similar aberrant modification of mesangial cell function by [Cl] and insulin was present in Dahl salt sensitive (DS) rats, which develop hypertension in a NaCl dependent manner. Similar to our previous reports on mesangial cells from normal rats, pre‐treatment with low [Cl] apparently attenuated Ca responses induced by angiotensin II and vasopressin in mesangial cells cultured from Dahl salt resistant (DR) rats. In contrast, this attenuation of vasoactive agents‐induced Ca signal was absent in the DS rat derived‐mesangial cells. Also, the enhancement of prostaglandin E2 production caused by decrease in [Cl] was not observed in the DS rat mesangial cells, while prostaglandin E2 production by DR rat mesangial cell was stimulated when [Cl] was decreased. In contrast, vasopressin‐induced Ca signal by insulin was attenuated in both DR and DS rat mesangial cells. Thus, in DS rat mesangial cells, modification of mesangial cell function by [Cl] was absent, but it was different from SHR mesangial cells because insulin was maintained.

Serum hepatocyte growth factor concentration in patients with various degrees of chronic renal failure

Summary: Serum hepatocyte growth factor (HGF) concentrations were measured in healthy volunteers, chronic renal failure patients without renal replacement therapy and haemodialysis patients. Serum HGF concentrations in healthy volunteers, chronic renal failure patients and haemodialysis patients were 0.18 ± 0.04 (s.d.), 0.28 ± 0.06 and 0.46 ± 0.22 ng/mL, respectively. Serum HGF concentration in chronic renal failure patients was significantly higher than that in healthy volunteers. Serum HGF concentration in haemodialysis patients was significantly higher than those in healthy volunteers and chronic renal failure patients. There was no regression of serum HGF concentration on age, sex, history of haemodialysis, prehaemodialysis serum creatinine concentration, and serum tumour necrosis factor (TNF)‐α concentration. We conclude that chronic renal disease and haemodialysis therapy are contributing factors to an increased serum HGF concentration.

Discrepant effects of vasoconstrictors on the growth of early passaged cultured rat mesangial cells

Summary: Mesangial cell growth stimulation by endothelin (ET) and arginine vasopressin (AVP) has been reported, but only in studies using late (3 times) pasaged cells. In the present study, we examined the effects of ET, AVP and platelet activating factor (PAF) on the proliferation of early (<3 times) passaged cultured rat mesangial cells which maintained their original characteristics. Cell growth was estimated by [3H]‐thymidine incorporation into DNA and by counting cell nuclei. After 48 h preincubation in minimal essential medium containing 0.5% fetal calf serum, ET‐1 (1‐100 nmol/L), AVP (100 pmol/L‐1 μmol/L) or PAF (1–100 nmol/L) was added to the incubation medium. In contrast to studies using late passaged cells, ET‐1 attenuated and AVP did not increase thymidine uptake (ET‐1: 18.4% inhibition at 10 nmol/L) or cell counts in early passaged cells, while the growth stimulatory effects of these agents were reproduced in late passaged cells. Platelet activating factor showed definite stimulation of cell growth in both early and late passaged cells in a dose‐dependent manner. These data strongly suggest that ET‐1 attenuates, and AVP does not stimulate, the cell growth of original mesangial cells. the PAF‐induced cell growth seems to be the constant feature of mesangial cells in vivo.