IGF-I and vanadate stimulate Na/Pi-cotransport in OK cells by increasing type II Na/Pi-cotransporter protein stability

 Insulin-like growth factor (IGF)-I and vanadate increase Na-dependent phosphate (Na/P_i) cotransport in opossum kidney (OK) cells. To gain more information about the mechanisms by which IGF-I and vanadate stimulate Na/P_i-cotransport, we measured type II Na/P_i-cotransporter (NaPi-4) protein abundance by Western blot analysis and investigated the effects of protein synthesis and tyrosine kinase inhibitors. The key findings in the present studies are as follows. First, incubation in IGF-I (10^–8 M) and/or vanadate (10^–3 M) for 3 h led to a non-additive 1.4-fold increase in Na/P_i-cotransport activity which was paralleled by a 1.5- to 2-fold increase in NaPi-4 protein. Second, actinomycin D did not abolish the increase in Na/P_i-cotransport and cycloheximide did not prevent the IGF-I-induced increase in Na/P_i-cotransport and NaPi-4 protein. Third, among the protein kinase inhibitors tested, only staurosporine substantially reduced the stimulation of Na/P_i-cotransport. In conclusion, the stimulatory effect of IGF-I on Na/P_i-cotransport is paralleled by an increased expression of NaPi-4 protein that is independent of protein synthesis and therefore results from increased protein stability. The observation that IGF-I and/or vanadate lead to similar increases in Na/P_i-cotransport and NaPi-4 protein abundance provides further evidence that the stimulation of Na/P_i-cotransport by IGF-I and vanadate involves protein tyrosine phosphorylation of the same signalling molecules. Received: 1 May 1998 / Received after revision: 25 August 1998 / Accepted: 1 September 1998     

Organic anion permeation at the proximal tubule of Necturus

This study deals with the electrical responses of the peritubular membrane of the Necturus proximal tubule to 8 organic anions, in NaHCO₃-free (trismaleate-buffered) and NaHCO₃-containing solutions. The anions glutamate and gluconate brought about a small depolarization, but only in NaHCO₃-free media. Benzene sulfonate did not alter significantly membrane p.d. The 5 other test-anions produced hyperpolarization. The magnitude of membrane depolarization elicited by high-K media was proportionally larger in the presence of the test-anions propionate, lactate, pyruvate, acetate and formate than with chloride: it is inferred that these anions increasedT _K. The same 5 anions shifted in the negative direction the p.d. achieved at peak K-depolarization; according to a previous analysis (Anagnostopoulos, 1977), this observation suggests that their permeabilities (P _A) are greater thanP _Cl, at least during the substitution. The association ofP _A>P _Cl with an increase ofT _K, upon exposure of the kidney to test-anions, is at best accounted for by a decrease ofP _Cl. The pattern of voltage attenuation along the epithelial cable during anionic substitutions is also consistent with an increase ofT _K via a decrease ofP _Cl. In conclusion, the apparent sequence of relative anionic permeabilities, as obtained from the responses of the tissue to a single anion, irrespective of buffering procedures, is:P _acet,P _lact,P _pyruv,P _prop,P _form>P _ClP _gluc,P _glut. The test-anions propionate, lactate, pyruvate, acetate and formate tend to increaseT _K, mainly by reducingP _Cl. The effect of glutamate and gluconate on physiologic ion permeabilities is too small to be specified with accuracy: it depends to some extent on the buffer used in the solutions.     

Contraluminal transport of hexoses in the proximal convolution of the rat kidney in situ

In order to study contraluminal hexose transport, concentration and time-dependent influx of³H-2-deoxy-d-glucose from the interstitium into cortical tubular cells has been measured. The influx curves fit to a two parameter kinetics (K _m 1.3±0.2 mmol/l,J _max 0.67±0.16 pmol/s · cm) plus an additional diffusion term (withP=6·10^–8 cm²/s) and a distribution ratio extracellular to intracellular amount of 2-deoxy-d-glucose of 10.6. Since the extracellular to intracellular free water space as estimated from morphological data was 12, one must conclude that glucose has only free access to 1/3 of the cell water. The intracellularly accessible space was augmented when the tubules were preperfused for 10 s with hypotonic saline. Thereby an increase of the compartment into which diffusion occurs was revealed and a final rupture of this intracellular compartment at 1/4 isotonic solutions was observed. Total replacement of ions in the peritubular perfusate by mannitol did not change 2-deoxy-d-glucose influx, indicating that it is Na⁺-independent. By adding isotonic concentrations of the respective sugars to the capillary perfusate, three degrees of inhibition of 2-deoxy-d-glucose influx could be revealed: strong inhibition byd-glucose, methyl--d-glucoside,d-mannose, 3-O-methyl-d-glucose, 2-deoxy-d-galactose, methyl--d-galactoside and 6-deoxy-d-glucose, moderate inhibition byd-galactose,l-glucose,l-mannose andd-fructose, no or borderline inhibition by methyl -d-glucoside, 2-deoxy-methyl--d-galactoside, 1-thio--d-glucose, 1-thio--d-galactose, 5-thio--d-glucose, myo-inositol and mannitol. The contraluminal 2-deoxy-d-glucose influx was also inhibited by phloretin, chlormerodrin and preperfusion with cytochalasin B. Starvation as well as streptozotocin diabetes has no influence on contraluminal 2-deoxy-d-glucose transport. Thus, in contrast to the luminal hexose transport system the contraluminal system is Na⁺-independent, does not require on OH-group at C-atom 2, acceptsl-glucose and fructose, but not an -methyl group at C-atom 1.     

Micropuncture studies on the filtration rate of single superficial and juxtamedullary glomeruli in the rat kidney

Summary Single nephron filtration rates of superficial and juxtamedullary nephrons were determined in high and low sodium rats. Single nephron GFR was calculated from TF/P inulin and tubular flow rate in superficial nephrons and single juxtamedullary GFR from corresponding data in long loops of Henle. In low sodium rats superficial nephron GFR was 23.5±6.4 (SD)×10^–6 ml/min×g KW, juxtamedullary nephron GFR was 58.2±13.6 and total kidney GFR (C _In) was 0.94±0.16 ml/min×g KW. Using these single nephron values, total kidney GFR and a total number of 30,000 glomeruli per kidney, the number of superficial and juxtamedullary glomeruli was calculated to be 23,267 and 6,733, respectively. During high sodium diet superficial nephron GFR increased to 38.1±11.3 and single juxtamedullary GFR decreased to 16.5±6.6, total kidney GFR increasing to 1.01±0.24. Calculation again revealed the same distribution of the two nephron types. End-proximal TF/P inulin in superficial nephrons was 2.36±0.36 in low sodium and 2.31±0.28 in high sodium rats. Loops of Henle TF/P inulin and intratubular flow rate were inversely related: the highest TF/P inulin values and lowest intratubular flow rates were found in the descending limb. These data quantify the distribution of superficial and juxtamedullary nephrons on a functional basis and suggest a mechanism by which the kidney adjusts sodium excretion by altering the contribution of each nephron type to total kidney GFR.Supported by the Deutsche Forschungsgemeinschaft and the U.S. Department of the Army, through its European Research Office.     

Ouabain decreases apparent potassium-conductance in proximal tubules of the amphibian kidney

According to a previous study from this laboratory, the electrochemical gradient for potassium across the peritubular cell membrane of proximal tubules in the isolated perfused frog kidney increases following the application of ouabain. In order to test, if this phenomenon were due to a decrease of potassium conductance, the effects of ouabain on cell membrane resistances and the sensitivity of the peritubular cell membrane potential difference (PD_pt) to step changes of peritubular potassium and bicarbonate concentration were studied. In the absence of ouabain, PD_pt averaged –60±3 mV (n=25). A step increase of peritubular potassium concentration from 3 to 18 mmol/l (pH 8.07) depolarises PD_pt (PD_k) by +24±2 mV (n=8). An increase of bicarbonate from 20 to 40 mmol/l (pH 8.07) hyperpolarises PD_pt (PD_b) by –2.8±0.4 mV (n=9). The resistance of the luminal and peritubular cell membranes in parallel (R _m) amounts to 45±9 k cm (tubule length) (n=4) and the voltage divider ratio (VDR) to 1.4±0.2 (n=7). The resistance of the cellular cable (cellular core,R _c) approaches 131±37 M/cm (n=4). Peritubular application of 0.1 mmol/l ouabain leads to a gradual decline of PD_pt (t _1/2 approx. 30 min), to an increase ofR _m, a decrease of PD_k and an increase of PD_b. VDR andR _c are not changed significantly. The data point to a functional link between the sodium/potassium ATPase and the potassium conductance of the peritubular cell membrane.     

Factors Influencing the Varus Deformity of Humeral Head in Proximal Humerus Fractures and Its Relation to Functional Outcome

BackgroundFractures of the proximal humerus represent approximately 4% of all fractures and 26% of humerus fractures. Proper reduction, stable internal fixation and early initiation of physiotherapy help to achieve a good functional outcome. Aim of this study was to evaluate varus fixation/malunion of proximal humerus fractures and its relation to functional outcome.Materials and MethodsWe retrospectively evaluated 32 patients with proximal humerus fractures who were surgically treated between 2015 and 2017 at tertiary care hospital. We divided the patients into three groups on the basis of the neck-shaft angle as valgus group, normal group and varus group to observe the influence of neck-shaft angle on efficacy. Patients were evaluated for functional outcome using the Constant–Murley score.ResultsTwo-part fractures had better functional outcome (Constant score = 75.15) compared to three parts with the moderate functional outcome (Constant score = 68.81) and the four-part fracture had poor functional outcome (Constant score = 52.66). After 6 months of follow-up, 13 patients had a neck-shaft angle of less than 126°. The functional outcome is significantly better among patients with normal neck-shaft angle and had a mean Constant score of 76.63 as compared to patients with varus deformity had a mean Constant score 60 (p = 0.001). 10 patients did not have medial support, in which 08 patients had neck-shaft angle less than 126° and 2 had a normal neck-shaft angle.ConclusionHigh fracture comminution, improper restoration of medial continuity causes varus deformity of the humeral head and it leads to poor functional outcome. The small sample size is the limitation of our study.     

Humeral Head Replacement in the Treatment of Comminuted Proximal Humeral Fracture

ObjectiveTo investigate the outcomes of humeral head replacement in the treatment of patients with comminuted proximal humeral fracture.MethodsBetween February 2013 and September 2016, 56 patients underwent humeral head replacement in our hospital. Of them, 18 cases were diagnosed as comminuted proximal humeral fracture before the operation. The mean age of the patients was 69.5 years old (ranging from 61 to 79 years old). Of them, there were six males and 12 females. All the patients in this group had fresh fractures. They were all treated by artificial humeral head replacements. After the prosthesis was fixed by bone cement reliably, the greater or lesser trochanter and prosthesis handle were sutured and fixed firmly. The interval time from injury to operation ranged from 1 to 5 days. The Constant Functional Score, operation time, blood loss, nerve injury, joint dislocation rate, and infection rate were recorded at the final follow‐up. The clinical data of these patients were retrospectively studied. All of the data were recorded in average form.ResultsIn this study, the mean duration of follow‐up was 4 years, ranging from 3 to 6 years. The operation time ranged from 75 to 120 min, with the average of 82 min. The blood loss ranged from 100 to 400 mL, with the average of 210 mL. The mean score of Constant Functional Score was 83.5 ± 3.1. Of them, 14 cases achieved excellent and good (scores of more than 80), and four cases achieved moderate and poor (scores of less than 80). No patient suffered from joint dislocation, unstable joint, or infection after the operation. There were two patients with axillary nerve injury before the operation. However, the function could be recovered within 3–6 weeks after the surgery.ConclusionThe artificial humeral head replacement could be applied for the treatment of patients with comminuted proximal humeral fracture. During the surgery process, the stable structure of shoulder joint could be completely restructured, and the rehabilitation plan should be adjusted reasonably and timely after the operation.     

Anatomic Repair of the Central Slip with Anchor Suture Augmentation for Treatment of Established Boutonniere Deformity

BackgroudThe rupture of the central slip of an extensor tendon of a finger causes a boutonniere (or buttonhole) deformity, characterized by pathologic flexion at the proximal interphalangeal (PIP) joint and hyperextension at the distal interphalangeal (DIP) joint. Currently, there are no standard treatment guidelines for this deformity. This study aimed to report clinical results of surgery to correct chronic boutonniere deformity.MethodsThis retrospective case series was conducted between January 2010 and December 2018 and only 13 patients with trauma-induced chronic deformity were included. After excision of elongated scar tissue, a direct anatomic end-to-end repair using a loop suture technique with supplemental suture anchor augmentation was conducted. Total active motion was assessed before and after surgery and self-satisfaction scores were collected from phone surveys.ResultsAll patients presented with Burton stage I deformities defined as supple and passively correctable joints. The initial mean extension lag of the PIP joint (43.5°) was improved by an average of 21.9° at the final follow-up (p < 0.001). The mean hyperextension of the DIP joint averaged 19.2° and improved by 0.8° flexion contracture (p < 0.001). The average total active motion was 220.4° (range, 160°–260°). Based on the Souter''s criteria, 69.2% (9/13) of the patients had good results. Only 1 patient reported fair outcome and 23.1% (3/13) reported poor outcome. The average Strickland formula score was 70 (range, 28.6–97.1). In total, 10 patients (77%) had excellent or good results. Of 10 patients contacted by phone, self-reported satisfaction score was very satisfied in 2, satisfied in 3, average in 3, poor in 1, and very poor in 1. Three patients reported a relapse of the deformity during range of motion exercises, 1 of whom underwent revision surgery. One patient complained of PIP joint flexion limitation, and 2 complained of DIP joint flexion limitation at final follow-up.ConclusionsIn chronic boutonniere deformity, central slip reconstruction with anchor suture augmentation can be an easily applicable surgical option, which offers fair to excellent outcome in 77% of the cases. The risk of residual extension lag and recurrence of deformity should be discussed prior to surgery.     

股骨近端髓内钉三维导航器的研制与测试

目的研发一种专用于防旋型股骨近端髓内钉置入时的三维导航器。方法选取颈干角为(135±5)°,并且股骨大转子顶点基本与股骨头中心等高的人体股骨骨骼的干标本32例,其中左侧16例,右侧16例。通过股骨头中心、平行于股骨干、垂直于股骨干与股骨颈所在的平面用钢锯将股骨标本的股骨头进行截骨;在股骨大粗隆顶端开口向股骨近端髓腔内插入PFNA主钉,主钉钉尾与股骨头中心点在同一高度上。在本课题所研发的股骨近端髓内钉三维导航器的导引下向股骨头颈部打入动力钉导引针,测量动力钉导引针在股骨头截骨面上的出针点与经股骨头中心点直线的垂直距离作为偏离值。结果利用本课题所研制的三维立体导航器在32例股骨骨骼的干标本上置入导引针,其中14例偏离值为0(占43.75%),最大偏离值为2mm,仅3例(占9.375%),平均误差只有0.69mm。结论本课题所研制的导航器结构简单,操作简便,定位精确,值得进一步在临床上研究应用。