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Biomedical subjects

L G Fine

Publications and source records attributed to L G Fine.

At least 73 records · Page 4Linked to original sources
PubMed1989

Polypeptide growth factors and the kidney.

Various polypeptide growth factors can act on different cell types in an autocrine, paracrine or endocrine manner. These bio-active peptides regulate molecular and cellular events that culminate in DNA synthesis and cell division. While, one or more polypeptides might be implicated as playing a predominant biological role in the kidney, in a given in vitro or in vivo situation, a network and cascade of events determines the final pattern of cell growth and response to injury. Elucidation of these molecular events and mechanisms of action of growth factors in the kidney is of fundamental importance to our understanding of both the normal development and disease states of the kidney.

Animals↗
PubMed1988

Prognostic implications of renal hypertrophy in diabetes mellitus.

Early in the course of type 1 diabetes mellitus, hypertrophy of the kidney is a consistent finding that is easily diagnosed using current noninvasive methods, especially ultrasonography. Renal functional changes occur in association with hypertrophy, most notably glomerular hyperfiltration. The structural counterpart of this functional change is an early increase in capillary filtration surface area. In most forms of nondiabetic renal hypertrophy, kidney size is closely linked to GFR. In contrast, in diabetes, persistence of hypertrophy after the clinical onset of overt kidney disease (microalbuminuria, hypertension, decreased GFR, etc.) suggests that sustained release of one or more growth factors may continue even after kidney function declines. The fact that growth factors can act in both an autocrine and paracrine fashion raises the possibility that the local effects of such substances may act as local mediators of kidney growth. Failure of renal hypertrophy to reverse following strict glycemic control for a few months may turn out to be an important prognostic indicator of future progression of the renal disease, but this remains to be established. Prospective studies of kidney size in patients with newly diagnosed type 1 diabetes, using accurate noninvasive methods, may be helpful in establishing whether irreversible ("autonomous") hypertrophy of the kidney is indeed a useful prognostic indicator. As therapies are developed that target the different microvascular complications of diabetes (retinopathy, nephropathy, neuropathy), a noninvasive estimation of kidney size may be a cost-effective method of predicting ultimate renal involvement. Since microalbuminuria occurs relatively late in the disease process, early and persistent hypertrophy of the kidney may become a useful prognostic test in the earliest stages of the disease.

Animals↗
PubMed1988

Patterns of mRNA expression during early cell growth differ in kidney epithelial cells destined to undergo compensatory hypertrophy versus regenerative hyperplasia.

An increase in cell size and protein content is characteristic of cells undergoing hypertrophy and of replicating cells prior to DNA synthesis. Cell enlargement in the two situations could be regulated by similar early events with an interruption of the cell cycle occurring in hypertrophy, or the two processes could be uncoupled. In vivo models were used to compare hypertrophy induced by unilateral nephrectomy and hyperplasia induced by folic acid injection in rabbit renal cortical cells. Within 48 hr, cell volume increased in both groups but the number of cells in the cell cycle and DNA synthesis was increased only after folic acid. Patterns of mRNA expression of the following three groups of cell cycle-dependent genes were analyzed: (i) protooncogenes (c-fos, c-myc, and c-Ha-ras), (ii) structural protein genes (vimentin and beta-actin), and (iii) transport protein genes (Na+, K+-ATPase, ADP-ATP translocase, and calcyclin). mRNAs for all genes, except calcyclin and c-Ha-ras, were detected in controls. Folic acid generally induced rapid, transient increases in mRNA levels, but after unilateral nephrectomy, expression of most mRNAs showed a gradual, progressive increase. These data indicate that gene expression in the early stages of cell enlargement differs in cells destined to undergo proliferation vs. hypertrophy. The term "sustained message amplification" is proposed to describe the hypertrophied cell.

Animals↗
PubMed1987

EGF-induced mitogenesis in proximal tubular cells: potentiation by angiotensin II.

The mitogenic effect of epidermal growth factor (EGF) and the characteristics of EGF binding were studied on primary cultures of rabbit proximal tubular cells. EGF was found to be a potent mitogen and stimulated DNA synthesis 18-fold above the level observed in quiescent cells. Using 125I-EGF as a ligand, two classes of specific EGF receptors were identified on the proximal tubular cell in culture, i.e., a high-affinity receptor with a dissociation constant (Kd) of 0.3 nM and maximal binding (Bmax) of 1.7 X 10(4) receptors/cell and a low-affinity receptor with a Kd of 1.9 nM and Bmax of 5.3 X 10(4) receptors/cell. Because angiotensin II (ANG II) appeared to possess many properties common to growth factors, we also examined the interaction of ANG II and EGF on these cells. ANG II was not mitogenic, but it potentiated the mitogenic effect of EGF with a maximal effect at 10(-9) M. The dose-response curve of EGF-induced mitogenesis was shifted to the left in the presence of 10(-9) M ANG II, decreasing the approximate half-maximal stimulatory concentration from 3 X 10(-8) to 5 X 10(-9) M. ANG II also stimulated prostaglandin E2 (PGE2) release, but inhibition of basal and ANG II-stimulated PGE2 synthesis had no effect on mitogenesis. ANG II had no effect on the binding of EGF to the high-affinity receptor from 1 to 20 h and did not alter receptor downregulation. ANG II (10(-9) M) had no effect on cell protein content, RNA and protein synthesis, Na+-H+ antiport, and intracellular free Ca2+ concentration. Higher concentrations of ANG II (5 X 10(-8) to 5 X 10(-6) M) led to a rapid and transient dose-dependent rise in cytosolic free Ca2+ concentration. These studies demonstrate that ANG II potentiates EGF-induced mitogenesis at one or more postreceptor steps that may include small changes in cytosolic Ca2+ concentration.

Angiotensin II↗
PubMed1986

Characteristics of the Na+-H+ antiporter in the intact renal proximal tubular cell.

The characteristics of the proximal tubular Na+-H+ antiporter were determined in isolated proximal tubular cells to ascertain whether the features of this transport system in intact cells are comparable with those previously described for isolated brush-border membrane vesicles. A method is described for the rapid isolation of a purified preparation of cells that demonstrate morphological and functional characteristics of the renal proximal tubule. The cells maintain their polarity while in suspension, and adenylate cyclase activity is enhanced by parathyroid hormone but not by arginine vasopressin. The cells display gluconeogenic function and Na+-dependent alpha-methyl-D-glucose and organic phosphate cotransport, processes that confirm their proximal tubule origin. O2 consumption rates and cytosolic adenosine triphosphate levels indicate functional integrity. Na+-H+ antiport activity was defined in these cells by measuring amiloride-sensitive Na+ uptake. At intracellular pH = 6.4 vs. extracellular pH = 7.4, KtNa was 10.1 +/- 2.8 mM, and maximal sodium flux was 0.89 +/- 0.13 nmol X 10(6) cells-1 X K0.5 for amiloride and ethyl-isopropyl amiloride, measured at an external Na+ concentration of 1 mM, was observed at 2.5 X 10(-5) M and 2.9 X 10(-6) M, respectively. The external and internal loci of the exchanger displayed asymmetric affinity for the hydrogen ion: the apparent pK for the external site was 7.20-7.26 vs. less than 6.5 for the internal site. The internal site demonstrated features of positive cooperativity. In summary, the Na+-H+ antiporter present in the luminal membrane of the renal proximal tubule has been characterized in the intact cell and displays functional and kinetic parameters closely resembling those described in isolated brush-border membrane vesicles.

Adenylyl Cyclases↗
PubMed1986

Proximal tubular cells in primary culture.

Primary cultures of mammalian proximal tubules (PT) can be established in serum-free, hormone-supplemented media. These cells attain confluence, demonstrate morphological polarity and exhibit vectorial fluid transport. Primary cultures of rabbit PT cells retain the transport properties of the parent cells and exhibit Na+-H+ exchange, Na+-Ca2+ exchange and Na-glucose co-transport, the latter process having kinetic properties comparable to those described for the late proximal tubule. Glucose which enters the cell via the luminal Na-glucose co-transport system undergoes metabolism to CO2; it is not clear whether this glucose oxidation, which is minimal in PT cells under physiological conditions, is due to selection of a specific cell type or to the nature of the culture conditions. Confluent, quiescent PT cells in culture can be induced to hypertrophy by addition of supraphysiological concentrations of insulin, PGE, and hypertonic NaCl; each stimulus also leads to an early increase in Na+-H+ antiport suggesting that this transport process may be causally related to the process of cell growth. The primary culture thus represents a promising model for future studies on the cellular events which govern the process of cell hypertrophy.

Adenylyl Cyclases↗
PubMed1985

[3H]Ethylpropylamiloride, a ligand to analyze the properties of the Na+/H+ exchange system in the membranes of normal and hypertrophied kidneys.

[3H]Ethylpropylamiloride is a useful radioactive label to identify the Na+/H+ exchange system (Vigne, P., Frelin, C., Audinot, M., Borsotto, M., Cragoe, E. J., and Lazdunski, M. (1984) EMBO J. 3, 2647-2651). This paper extends the analysis of the properties of interaction of [3H]ethylpropylamiloride with the exchanger and describes its use with hypertrophied kidneys. [3H]Ethylpropylamiloride-binding sites copurify with the luminal membrane marker alkaline phosphatase but not with the basolateral membrane marker (Na+,K+)ATPase, thus indicating an asymmetric distribution of the Na+/H+ exchanger. Specific [3H]ethylpropylamiloride binding is dependent on pH. The pH dependency indicates that an ionizable function with a pKapp of 7.0 is essential in the association of the amiloride derivative. H+ acts competitively on [3H]ethylpropylamiloride binding; Na+, Li+, or cholinium ions have no effect on the association. Compensatory adaptation of the kidney to chronic reduction of renal mass is accompanied by a 1.7-fold increase in the activity of the Na+/H+ exchange system. Properties of interaction of internal and external pH with the Na+/H+ exchanger of normal and hypertrophied kidneys are identical. Titration of [3H]ethylpropylamiloride-binding sites in normal and hypertrophied kidneys suggests that the increased activity of the Na+/H+ exchange system is not accompanied by an increased concentration of exchangers.

Amiloride↗
PubMed1985

BSC-1 growth inhibitor transforms a mitogenic stimulus into a hypertrophic stimulus for renal proximal tubular cells: relationship to Na+/H+ antiport activity.

Renal hypertrophy is characterized by an increase in cell size and protein content with minimal hyperplasia. The mechanisms of control of this pattern of cell growth have not been determined. The present studies examined whether the growth inhibitor elaborated by BSC-1 kidney epithelial cells (GI), which has nearly identical biological properties to transforming growth factor beta (TGF-beta), could transform a mitogenic stimulus into a hypertrophic stimulus for rabbit renal proximal tubular cells in primary culture. Insulin (10 micrograms/ml) plus hydrocortisone (50 nM) increased the amount of protein per cell, cell volume, and [3H]thymidine incorporation at 24 and 48 hr in these cells. GI/TGF-beta (10 units/ml) led to a minimal stimulation of [3H]thymidine incorporation. When added together with insulin plus hydrocortisone, GI/TGF-beta inhibited the stimulatory effect of these mitogens on [3H]thymidine incorporation but did not block the increase in protein per cell and cell volume--i.e., the cells underwent hypertrophy. The fact that this pattern persisted for 48 hr indicated that GI/TGF-beta exerted a prolonged inhibitory effect on mitogenic-stimulated DNA synthesis rather than delaying its onset. Amiloride-sensitive Na+ uptake (indicative of Na+/H+ antiport activity) correlated with protein per cell and cell volume rather than with DNA synthesis. P60 gel chromatographic fractionation of conditioned medium harvested from proximal tubular cells yielded a fraction that inhibited [3H]thymidine incorporation in BSC-1 cells and CCL 64 cells; the relative inhibitory activity on these cell lines and the chromatographic behavior were similar to those observed with GI/TGF-beta. These studies indicate that the control of cell size may be regulated by autocrine mechanisms mediated by the elaboration of growth inhibitory factors that alter the pattern of the growth response to mitogens.

Animals↗
PubMed1985

Stimulation of Na+/H+ antiport is an early event in hypertrophy of renal proximal tubular cells.

Renal hypertrophy in vivo is achieved by an increase in protein content per cell and an increase in cell size with minimal hyperplasia. Hypertrophied renal tubular cells remain quiescent and demonstrate an increase in transcellular transport rates. This situation was simulated in vitro by exposing a confluent, quiescent primary culture of rabbit renal proximal tubular cells to either insulin, prostaglandin E1, or hypertonic NaCl for 24 or 48 hr. Protein per cell increased by 20-30% with little or no increase in [3H]thymidine incorporation into DNA. Mean cell volume was also increased in insulin- and hypertonic NaCl-treated but not in prostaglandin E1-treated cells. The lag period required to initiate DNA synthesis by a combination of insulin and hydrocortisone was the same in control and hypertrophied cells, indicating a quiescent state of the latter. Two hours of exposure to the growth stimuli increased amiloride-sensitive Na+ uptake, Na-dependent H+ efflux, and ouabain-sensitive Rb+ uptake, indicating that stimulation of Na+/H+ antiport (exchange) occurs as an early event in their action. Hypertrophied cells continued to demonstrate enhanced Na+/H+ antiport after the growth stimuli were removed for 3 hr, by which time their acute effects are reversed.

Alprostadil↗
PubMed1985

pH gradient-dependent increased Na+-H+ antiport capacity of the rabbit remnant kidney.

The adaptative response of the renal proximal tubule to a reduction of renal mass was studied in brush border membrane vesicles prepared from the solitary remnant kidney (RK) of subtotally nephrectomized rabbits. The in vivo acid-base status of RK and sham-operated controls (SK) was similar. In the absence of organic solutes, Na+ flux across the membrane demonstrated features of Na+-H+ antiport, i.e., stimulation by a transmembrane pH gradient and inhibition by amiloride. Kinetic parameters for Na+-H+ antiport were derived with different experimental protocols. In the presence of an opposing H+ gradient and over a limited range of Na+ concentration, JNamax was enhanced 65% in RK vesicles compared with SK vesicles and KtNa was unchanged. The enhanced JNamax was not apparent under H+ equilibrium conditions, Comparable values for JNamax and KtNa were obtained by studying RK vesicles at external Na+ concentrations of 0-200 mM and resolving uptake into a substrate component, representing Na+-H+ antiport, and a nonsaturable diffusive component. The apparent Na+ permeability (P'Na) of RK vesicles was identical to the P'Na of normal kidney vesicles, under both H+ gradient and H+ equilibrium conditions. H+ permeability, measured with acridine orange, was also the same in RK and SK vesicles. These studies demonstrate that in the remnant kidney model of chronic renal insufficiency there is an increase in the JNamax of the Na+-H+ antiporter in the luminal membrane of the proximal tubule that is revealed only under transmembrane H+ gradient conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Acid-Base Equilibrium↗