Ca2+ uptake by endoplasmic reticulum of renal cortex. I. Ionic requirements and regulation in vitro

A subcellular fraction enriched in cytochrome c reductase (7.9-fold) and relatively de-enriched (0.64-fold) in Na+/K(+)-ATPase was prepared from canine kidney cortex by sucrose density gradient ultracentrifugation. It was shown by electron microscopy to consist primarily of a light fraction of endoplasmic reticulum (LER). LER vesicles displayed ATP-dependent 45Ca2+ uptake that was insensitive to 10 mM KCN or NaN3, and was promptly released by 20 microM A23187 or ionomycin. Inositol-1,4,5-trisphosphate (IP3) appeared to produce a time-dependent release of 45Ca2+. Vanadate inhibited 45Ca2+ uptake with a Ki approximately 0.3 mM, further suggesting that the activity resided in the ER rather than the plasma membrane. 45Ca2+ uptake by LER, at 5 microM total [Ca2+], displayed a strong dependence on divalent cations (Mg2+ greater than Co2+ greater than Mn2+ much greater than Ba2+ greater than or equal to Cd2+ greater than or equal to Sr2+, present at 2 mM) as well as on monovalent cations (Na+ greater than or equal to K+ + Na+ greater than K+ greater than Li+ greater than choline +), and anions (Cl- greater than acetate- greater than or equal to NO3- greater than or equal to F- greater than H2PO4- much greater than gluconate- greater than or equal to oxalate= much greater than SO4=). It had a fairly narrow pH optimum (7.25-7.50). Preincubation (10 min) of LER vesicles with 12-O-tetradecanoylphorbol-13-acetate (TPA) stimulated LER Ca2+ uptake; this effect was enhanced in the presence of renal cytosol [5% (vol/vol)].(ABSTRACT TRUNCATED AT 250 WORDS)

Ca2+ uptake by endoplasmic reticulum of renal cortex. II. Effects of uninephrectomy and parathyroidectomy

Calcium uptake by the endoplasmic reticulum (ER) is important for cellular calcium homeostasis, yet its regulation in nonmuscle cells is poorly understood. We reported that Ca2+ uptake by a light fraction of canine renal cortical ER (LER) is stimulated by protein kinase C in vitro. Here we describe conditions in vivo that stimulate renal cortical LER Ca2+ uptake. Thirty minutes after contralateral nephrectomy in the dog, 45Ca2+ uptake into renal cortical LER was increased 42% above control LER. There was no difference in LER Ca2+ uptake 24 hours after uninephrectomy. Acute denervation did not reproduce the increase in LER 45Ca2+ uptake seen at 30 minutes after uninephrectomy, nor did prior thyroparathyroidectomy abolish it. Forty-eight hours after thyroparathyroidectomy, 45Ca2+ uptake activity into renal cortical LER was decreased approximately sevenfold. In a proximal tubular cell line (LLC-PK1), 30-minute incubation with 12-O-tetradecanoylphorbol-13-acetate doubled 45Ca2+ uptake into a nonmitochondrial pool. Pretreatment with epidermal growth factor halved ER Ca2+ uptake, whereas insulin-like growth factor and growth hormone, alone or in combination, had no effect. Our data suggest that Ca2+ uptake into renal cortical ER is stimulated acutely during compensatory renal growth, perhaps through protein kinase C, and is stimulated chronically by parathyroid hormone.

Regional and subcellular distribution of [125I]endothelin binding sites in rat brain

The binding of [125I]endothelin-1 (125I-ET-1) to membranes from whole rat brain, from individual brain regions, and derived from subcellular fractionation of whole rat brain was investigated. 125I-ET-1 binding to whole rat brain membranes was rapid, concentration-dependent, saturable, and characterized as irreversible because it was not displaced by unlabeled endothelin-1 (ET-1) and different concentrations of ligand produced, with time, a similar magnitude of binding. The maximum binding site capacity and second-order forward rate association constant of binding were 1,946 +/- 147 fm/mg protein and 5.53 +/- 1.72 x 10(6) M-1 s-1. Removal of either extramembranal calcium or membrane-bound calcium and calcium binding proteins did not affect the binding of 125I-ET-1 to whole rat brain membranes. The brain stem and cerebellum contained the highest levels of 125I-ET-1 binding sites, whereas the cerebral cortex, striatum, and hippocampus contained binding site levels three- to fourfold less. Subcellular fractionation of whole rat brain and subsequent analyses of the distribution of 125I-ET-1 binding demonstrated a twofold enrichment of binding sites in the synaptosomal fraction compared to the homogenate. The myelin fraction contained a similar density of binding sites compared to the homogenate, while the mitochondrial and microsomal fractions contained considerably less binding sites. The ribosomal fraction did not contain any 125I-ET-1 binding sites. The subcellular distribution of 125I-ET-1 binding sites did not correlate with the distribution of 5'-nucleotidase, cytochrome-C oxidase, phosphodiesterase, and alkaline phosphatase. Depletion of extracellular calcium increased 125I-ET-1 binding in the synaptosomal fraction but not in the myelin and mitochondrial fractions.(ABSTRACT TRUNCATED AT 250 WORDS)

Spatiotemporal changes in Ha-ras p21 expression through the hepatocyte cell cycle during liver regeneration

The protein product of the ras oncogene, Ha-ras (p21), is thought to be an important regulator of cell growth. The cytoplasmic relocalization of p21 in the cell during the cell cycle suggests a transient signaling role for this protein in association with its signal transduction function. Because of the importance of this role we examined spatial patterns in vivo of p21 expression at the protein and mRNA levels in hepatocytes during compensatory growth in rat liver following partial hepatectomy. A low level of p21 was immunolocalized on the cytoplasmic membrane of nonregenerating hepatocytes. The level of hepatic p21 increased significantly and without spatial restriction within the liver from 36 to 60 hr after partial hepatectomy (PH). p21 was localized in the cytoplasm of dividing hepatocytes and on the hepatic cytoplasmic membrane. The elevated p21 level decreased and was found mainly on hepatocyte plasma membranes by 96 hr after PH. Immunogold electron microscopy showed p21 localized over mitochondrial membranes and nuclei in nondividing regenerating hepatocytes. Approximately 50% of nonregenerating hepatocytes show nuclear localization of p21. This percentage changes with time following PH. The decrease in nuclear localization was accompanied with an increase in the low number of hepatocytes which demonstrated cytoplasmic localization in nondividing hepatocytes in regenerating liver. Flow cytometric analysis revealed a significant increase of p21 at 36 hr after PH which was 12 hr after the initial induction of ras mRNA. ras mRNA level increased 1.5-fold at 24 hr after PH and a maximum twofold induction was observed at 48 hr. Cell-cycle analysis of regenerating hepatocytes indicated a synchronized first peak of cell division 36-40 hr after PH. Dual parameter flow cytometry revealed that the level of p21 in hepatocytes in S phase and G2/M phase of the cell cycle was significantly higher than that in G0/G1 phase during regeneration. These findings suggest that p21 is important for the progression of regenerating hepatocytes to S phase and then to G2/M phase.

[The anesthetic site of action: from the intact brain to the isolated protein. An overview]

To the present day there is no consensus of opinion as to which molecular events lead to the complex clinical state generally referred to as anaesthesia. The multitude of simultaneous physiological changes are also responsible for this lack of consensus. During anaesthesia, for example, consciousness, perception, memory, pain, and muscle relaxation are altered. The actions of anaesthetics correlate very well with their partitioning into lipophilic phases. Lipophilic interactions are non-specific. Therefore, it is likely that anaesthetics act at many different sites. Cell membranes are not the only possible sites but also membrane proteins and the various hydrophobic domains they contain. The multitude of clinical anaesthetic effects is paralleled by the complexity of molecular interactions. A better understanding of anaesthesia requires an integrated view of anaesthetic effects at the various systemic levels, beginning with the molecular domain and ending with the intact central nervous system. Anaesthesia research could be directed more towards man because it has now become possible to conduct molecular in-vitro studies with human cells as well as non-invasive studies of the intact human central nervous system.

Signal transduction in smooth muscle as studied by the subcellular membrane approach

Many of the contractile regulatory events in smooth muscle reside in various cellular membrane components as functional membrane constituents that interact in a variably complex manner. The physiological handling of ionized calcium (Ca2+), which serves multiple roles as an extracellular signal, a second messenger, and an activator interacting directly with myofilaments to effectuate contractile responses, referred to as Ca2+ signalling processes, represents an integral part of a more complicated membrane transduction mechanism. The subcellular membrane approach toward the understanding of Ca2+ signalling as well as the transduction mechanisms involving membrane receptors, GTP binding proteins, ion channels, membrane-bound enzymes, and the production of intracellular second messengers has made a significant contribution in smooth muscle research for the past decade. This review summarizes the current state of knowledge about the multiplicity of interactions between Ca2+ and various membrane constituents in the surface membranes and sarcoplasmic reticulum, such as Ca2+ binding, Ca2+ ATPase pumps, Ca2+ channels, and Ca2+Na+ or related ion exchangers. A number of recent novel findings from this laboratory have also been discussed. First of all, the technical refinement of membrane separation and characterization, which permits better identification of neuronal membranes in highly innervated smooth muscle tissues, led to the distinction of prejunctional and postjunctional membrane receptors. Secondly, unlike the Ca(2+)-release channels labelled with [3H]inositol 1,4,5-trisphosphate, the other type of internal membrane Ca(2+)-release channels labelled by [3H]ryanodine has been identified only recently in smooth muscle.(ABSTRACT TRUNCATED AT 250 WORDS)

Subcellular and molecular mechanisms of bile secretion

One of the liver's principal functions is the formation of bile, which is requisite for digestion of fat and elimination of detoxified drugs and metabolites. Bile is a complex fluid made up of water, electrolytes, bile acids, pigments, proteins, lipids, and a multitude of chemical breakdown products. In this review, we have summarized the source of various biliary components, the route by which they end up in bile, including the underlying subcellular and molecular mechanisms, and their contribution to bile formation. One of the reasons why bile formation is so complex is that there are many mechanisms with overlapping substrate specificities, i.e., many biochemically unrelated biliary constituents share common transport mechanisms. Additionally, biliary constituents may reach bile by more than one pathway. Some biliary components are critical for bile formation; others are of minor significance for bile formation but play a major physiological role. The major driving force for bile formation is the uptake and transcellular transport of bile salts by hepatocytes. The energy for bile formation comes from the sodium gradient created by the basolateral Na+/K(+)-ATPase, to which bile salt transport is coupled. The secretory pathway for bile salts involves uptake at the basolateral surface of the hepatocyte, vectorial transcellular movement, and transport across the canalicular membrane into the canalicular lumen. Hydrophilic bile salts are taken up via a sodium-dependent, saturable, carrier-mediated process coupled to the Na+/K(+)-ATPase. This uptake mechanism is also shared by other substrates, such as electroneutral lipids, cyclic oligopeptides, and a wide variety of drugs. Hydrophobic bile acids are taken up by a sodium-independent facilitated carrier-mediated mechanism in common with other organic ions, including sulfated bile acids, sulfobromophthalein, bilirubin, glutathione, and glucuronides, or by nonsaturable passive diffusion. Two major carrier proteins have been identified on the hepatocyte basolateral membrane: a 48-kDa protein that appears to be involved with Na(+)-dependent bile salt uptake, and a 54-kDa protein, thought to be associated with Na(+)-independent bile salt uptake. The intracellular transport of bile salts may involve cytosolic carrier proteins, of which several have been identified. Some evidence suggests a vesicular transport mechanism for bile salts. Since bile acids clearly do not enter the cell by endocytosis, formation of transport vesicles must be a more distal event in the transcellular translocation process. Some bile salts appear to be transported within the same unilamellar vesicles that are involved in the secretion of cholesterol and phospholipid.(ABSTRACT TRUNCATED AT 400 WORDS)

Reactivation of newt lung cilia: evidence for a possible temperature- and MgATP-induced activation mechanism

Optimal conditions have been developed for the isolation and reactivation of highly coupled, demembranated ciliary axonemes from newt lungs [Hard, Cypher, and Schabtach, 1988, Cell Motil. Cytoskeleton 10:271-284]. In the present study, the motility of these cilia was further characterized by examining the effects of nucleotides, divalent cations, and temperature on beat frequency. When exposed to a reactivating solution containing Mg2+ and ATP, nearly 100% of the axonemes were motile and beat at frequencies of 0-50 Hz, depending on [MgATP] and temperature. Divalent cations were required for movement, with Mg2+ 2-3 times more effective than Ca2+. There was no absolute requirement for Ca2+ for motility. The beat frequencies obtained with fixed ATP and varying Mg2+ concentrations indicate that MgATP serves as the actual substrate. The effects of MgATP on beat frequency depended on the degree of mechanochemical coupling and temperature. When highly coupled preparations were reactivated at 21 degrees C, double reciprocal plots of beat frequency vs. [MgATP] were biphasic with extrapolated Fmax values of 22 and 44.8 Hz. However, when reactivated at 10 degrees C and 30 degrees C, linear plots were generated with Fmax values of 18.3 and 48.9 Hz, respectively. The beat frequencies of cultured cells and reactivated axonemes also varied biphasically with temperature. Our data suggest that newt lung respiratory cilia possess an intra-axonemal activation mechanism involving a temperature- and MgATP-induced transition between two distinct states whose maximum beat frequencies differ by 200-300%.

Response of Escherichia coli cell membranes to induction of lambda cl857 prophage by heat shock

Heat shock induces protein aggregation in Escherichia coli and E. coli (lambda cl857). The aggregates (S fraction) appear 15 min post-induction and are separable from membranes by sucrose density-gradient centrifugation. The S fraction quickly disappears in wild type strains but persists in rpoH mutant with concomitant quick inner membrane destruction. We propose that: (1) the disappearance of the S fraction reflects a rpoH-dependent processing, (2) the membrane destruction explains the lethality of the rpoH mutation at elevated temperatures; and (3) the protection of the inner membrane integrity is an important physiological function of the heat-shock response. We assume that the S fraction of aggregated proteins represents the signal inducing the heat-shock response. The prophage thermo-induction results in an increase (35 min post-induction) in the A fraction resembling that of the adhesion zones of the membranes. This fraction is greater than the corresponding fraction from uninduced cells. The increase is mediated by the lambda late genes, since it is absent in the induced E. coli (lambda cl857 Qam21). Since heat shock is widely used for induction of the lambda promoters in expression vectors it is possible that the formation of the protein aggregates (though transient in WT strains) and/or the fragility of membranes in rpoH mutants may be the cause of poor expression of cloned genes or may lead to mistaken localization of their expression products.

Ultrastructural distribution of glutamate immunoreactivity within neurosecretory endings and pituicytes of the rat neurohypophysis

An ultrastructural analysis of post-embedding glutamate immunocytochemistry within the neural lobe of the pituitary was used to explore the possible role of glutamate within the magnocellular neuroendocrine cells. Relative densities of a colloidal gold marker associated with various cellular and subcellular compartments of the neural lobe were quantified by computer analysis of electron micrographs. Robust glutamate immunoreactivity was observed in both pituicytes (cytoplasm, mitochondria and nucleus) and neurosecretory endings. Within the neurosecretory endings, glutamate staining was specifically localized to the microvesicles with no overlap into the neurosecretory granule population. Stimulation of the vasopressin/oxytocin neurosecretory system by water deprivation increased glutamate content in pituicytes and mitochondria within neurosecretory endings but had little influence on microvesicle glutamate content. The results are consistent with the existence of multiple functional pools of immunoreactive glutamate in both pituicytes and neurosecretory endings. Microvesicles within the neurosecretory endings exhibit many properties of secretory vesicles, appear to be functionally independent of the neurosecretory granules, and have sufficient glutamate immunoreactivity to suggest that this amino acid may be compartmentalized for release in the neural lobe.

Temporal segregation of surfactant secretion and lamellar body biogenesis in primary cultures of rat alveolar type II cells

Pulmonary alveolar type II cells synthesize and secrete the phospholipids of surfactant. However, type II cells isolated from adult rat lungs rapidly lose their characteristic morphology and differentiated functions (such as surfactant-specific phospholipid and protein biosynthesis) when maintained on tissue culture plastic. In this study, phospholipid secretion and its regulation by type II cells grown on tissue culture plastic were examined up to 8 days after isolation. Type II cells were preincubated with [3H]choline for varying 24-h periods during culture prior to examining phosphatidylcholine ([3H]PtdCho) secretion. Type II cells cultured for 4 days and incubated with [3H]choline 24 h before the secretion experiment failed to show significant basal and tetradecanoyl phorbol acetate (TPA, 100 nM)-stimulated [3H]PtdCho secretion (basal, 0.29 +/- 0.01%; TPA, 0.48 +/- 0.04%). In contrast, type II cells incubated with [3H]choline for the first 24 h during culture and then cultured for 3 more days showed significant [3H]PtdCho secretion (basal, 1.27 +/- 0.19%; TPA, 6.24 +/- 0.82%). Subcellular fractionation of type II cells revealed that [3H]choline was incorporated into phosphatidylcholines in a lamellar body-enriched fraction during the first 24 h of culture but that the assimilation of phosphatidylcholine into the lamellar body fraction progressively declined with increasing time in culture. Radiolabel incorporated into the lamellar body fraction labeled during the first 24 h of culture was detectable for up to 8 days in culture. The [3H]PtdCho incorporated into the lamellar body during the first 24 h of culture was lost gradually over 8 days, suggesting the continuous secretion or turnover of the lamellar bodies during culture.(ABSTRACT TRUNCATED AT 250 WORDS)

The identity of the calcium-storing, inositol 1,4,5-trisphosphate-sensitive organelle in non-muscle cells: calciosome, endoplasmic reticulum ... or both?

Although the initial phase of receptor-mediated Ca2+ signaling, involving Ca2+ release from intracellular stores by inositol 1,4,5-trisphosphate, is relatively well characterized, the nature of the organelle releasing Ca2+ is a controversial subject. At issue is the question of whether Ca2+ is released from the endoplasmic reticulum, or from a more specialized organelle called the 'calciosome'. In this review, we attempt to analyse the arguments for and against these two views, and attempt to reconcile some of the apparently conflicting findings by proposing a hypothetical model of the inositol 1,4,5-trisphosphate-sensitive Ca2+ pool.

Scaling concepts in cellular and subcellular dynamics

After developing a map for certain states typical of hemopoietic stem cells (SCs), we identify a number of parameters (e.g. fractal dimensions, oscillatory behavior in a multistable landscape, etc.) that scale down to subcellular structures such as interphase genome, chromatids, chromatin entanglements and DNA segmental motions. A curious aspect is the continuous reappearance of recursive processes even at very small biologic scales. These iterations are relevant not only for the normal behavior of (hemopoietic) cells but also for amplifying hidden genomic singularities above some critical threshold. When that happens, there are sudden quali-quantitative and often clonal changes in the cell behavior. As illustrated by specific leukemic cases, many paradoxes of malignant growth seem best explained by the peculiar sensitivity to initial condition of (hemopoietic) cells. Interpreted as chaotic oscillators, these cells display a spectrum of disorders that, in spite of appearing as random, are in fact triggered by amplification of subtle preconditions with statistico-deterministic outcomes, that are predictable within certain time limits.

Neutral and acid retinyl ester hydrolases associated with rat liver microsomes: relationships to microsomal cholesteryl ester hydrolases

We recently reported the presence of a neutral, bile salt-independent retinyl ester hydrolase (REH) activity in rat liver microsomes and showed that it was distinct from the previously studied bile salt-dependent REH and from nonspecific carboxylesterases (Harrison, E. H., and M. Z. Gad. 1989. J. Biol. Chem. 264: 17142-17147). We have now further characterized the hydrolysis of retinyl esters by liver microsomes and have compared the observed activities with those catalyzing the hydrolysis of cholesteryl esters. Microsomes and microsomal subfractions enriched in plasma membranes and endosomes catalyze the hydrolysis of retinyl esters at both neutral and acid pH. The acid and neutral REH enzyme activities can be distinguished from one another on the basis of selective inhibition by metal ions and by irreversible, active site-directed serine esterase inhibitors. The same preparations also catalyze the hydrolysis of cholesteryl esters at both acid and neutral pH. However, the enzyme(s) responsible for the neutral REH activity can be clearly responsible for the neutral REH activity can be clearly differentiated from the neutral cholesteryl ester hydrolase(s) on the basis of differential stability, sensitivity to proteolysis, and sensitivity to active site-directed reagents. These results suggest that the neutral, bile salt-independent REH is relatively specific for the hydrolysis of retinyl esters and thus may play an important physiological role in hepatic vitamin A metabolism. In contrast to the neutral hydrolases, the activities responsible for hydrolysis of retinyl esters and cholesterol esters at acid pH are similar in their responses to the treatments mentioned above. Thus, a single microsomal acid hydrolase may catalyze the hydrolysis of both types of ester.(ABSTRACT TRUNCATED AT 250 WORDS)

Organization and dynamics of microtubules in Torpedo marmorata electrocyte: selective association with specialized domains of the postsynaptic membrane

The distribution and subcellular organization of two components of the secretory pathway, the Golgi apparatus and microtubules, have been investigated in Torpedo marmorata electrocyte. This highly polarized syncytium, embryologically derived from skeletal muscle cells, displays distinct plasma membrane domains on its innervated and non-innervated faces, and it played a critical role in the identification of the acetylcholine receptor. By immunocytochemical analysis, we show that in the electrocyte, numerous focal Golgi bodies are dispersed throughout the cytoplasm in frequent association with nuclei. Under experimental conditions known to stabilize microtubules, we reveal an elaborate network composed of two populations of microtubules exhibiting different dynamic properties as evaluated by cold-stability, resistance to nocodazole and post-translational modification. This network appears organized from several nucleating centers located in the medial plane of the cell that are devoided of centrioles. The network displays an asymmetric distribution with individual microtubules converging towards the troughs of the postsynaptic membrane folds. In these particular regions, we consistently observed clusters of non-coated vesicles in association with the microtubules. The organization of the microtubules in the electrocyte may thus result in a functional polarization of the cytoplasm. In other polarized cells, the particular organization of the secretory pathway accounts for the intracellular routing of membrane proteins. The organization that we have observed in the electrocyte may thus lead to the vectorial delivery of synaptic proteins to the innervated plasma membrane. Furthermore, the abundance of synaptic proteins makes the electrocyte a unique model with which to decipher the mechanisms involved in the sorting and targeting of these glycoproteins.

The assembly of lipids into lipoproteins during secretion

The process of assembly and secretion of lipoproteins is discussed with particular reference to the role of lipids. The majority of circulating lipoproteins is produced by the liver (80%) with the remainder being supplied by the intestine. The liver secretes both very low density lipoproteins and high density lipoproteins, but the assembly and secretion of these two types of particles may follow different routes. The major lipid components of lipoproteins are triacylglycerols, cholesterol, cholesterol esters and phospholipids. The biosynthesis of these lipids occurs on membranes of the endoplasmic reticulum, with many of the enzymes also being present in the Golgi; the roles of these two subcellular organelles in the assembly of lipoproteins are discussed. There appears to be a compartmentalization of lipids in cells, such that defined pools, often those newly-synthesized, are preferred, or even required, for lipoprotein assembly. The process of hepatic very low density lipoprotein secretion appears to be regulated by the supply of lipids. Indeed, the synthesis of new lipid may be a major driving force in lipoprotein assembly and secretion.

Studies on the expression of intracellular and surface polarity in animal pole cells of Xenopus embryos cultured on various substrata

The expression of intracellular and surface polarity in animal pole cells of Xenopus embryos (stage 10) cultured on various substrata was studied by electron microscopy. When animal pole cells of Xenopus embryos were cultured on type I collagen- or gelatin-coated dishes until control embryos reached stage 23, the cells in confluent layers expressed an apical-basal polarity so that the apical surface membrane domain faced the culture medium. However, the cells in confluent layers cultured on naked plastic dishes were suppressed to express intracellular and surface polarity. In addition, single attached cells which were formed by being sparsely plated neither spread on any substrata nor displayed the apical-basal polarity perpendicular to the dishes. These results indicate that the expression of intracellular and surface polarity in cultured animal pole cells of Xenopus embryos requires not only cell-cell contact but also an adhesive substrata such as type I collagen or gelatin.

Subcellular distribution and physicochemical properties of scrapie-associated precursor protein and relationship with scrapie agent

We studied the biologic properties of hamster-adapted scrapie (strain 263K) and its relationship to the precursor protein of scrapie (PrP33-35Sc). The highest titer of infectious material and the greatest concentration of PrP33-35Sc were in the fractions containing microsomal and synaptosomal membranes. We found traces of infectivity in the absence of PrP33-35Sc associated with matrix protein. Partitioning of membranes with neutral chloroform-methanol resulted in concentration of PrP33-35Sc and infectivity within the interphase layer. Recombination of membrane glycoproteins (interphase) with lipids extracted from homologous brains decreased infectivity greater than or equal to 4 logs. Temperature-dependent phase separation of infected synaptosomal and microsomal membranes with Triton X-114 yielded a phospholipid-rich phase containing a high concentration of PrP33-35Sc and greatest infectivity titers. This material spontaneously formed liposomes, indicating that PrP33-35Sc and PrP33-35C precursor proteins are highly hydrophobic intrinsic membrane components integrated with phospholipids. Homologous membrane phospholipids appear to prevent aggregation of the scrapie isoform of PrP and maintain high levels of infectivity.

Human platelet-derived mitogens. II. Subcellular localization of insulinlike growth factor I to the alpha-granule and release in response to thrombin

Platelets contain mitogenic activities for MCF-7 human breast cancer cells when assayed under serum-free chemically defined conditions. Purification from outdated human platelets identified insulinlike growth factor I (IGF-I) as the most potent breast cancer cell mitogen in lysates (Karey KP, Sirbasku DA: see accompanying article, this issue). In this study the release and subcellular localization of IGF-I was investigated. Degranulation of platelets by thrombin treatment caused release of lysosomal enzymes (beta-glucuronidase and N-acetyl-D-glucosaminidase), alpha-granule proteins (beta-thromboglobulin and fibrinogen) as well as mitogenic activity for MCF-7 cells and IGF-I as measured by radioimmunoassay (RIA) and radioreceptor assay. Release of mitogenic activity and immunologically identified IGF-I was induced tenfold over controls by thrombin and was nearly complete as compared to platelets disrupted by repeated freezing and thawing. Disruption of platelets by nitrogen cavitation followed by separation of the organelles by sucrose density gradient sedimentation showed that IGF-I and mitogenic activity localized predominantly to fractions containing alpha-granules rather than soluble cellular components, lysosomes, or dense granules. The morphology of MCF-7 cells in serum-free medium supplemented with supernatants from thrombin-treated platelets also indicated the release of important cell-adhesion factors for human breast cancer cells.

Neutrophil activating factor (NAF) induces polymorphonuclear leukocyte adherence to endothelial cells and to subendothelial matrix proteins

Neutrophil activating factor is a polypeptide cytokine released from stimulated mononuclear phagocytes and endothelial cells. We found that neutrophil activating factor induced time- and concentration-dependent binding of human polymorphonuclear leukocytes to endothelial monolayers and subendothelial matrix proteins, via a mechanism that involves altered expression of the leukocyte CD11/CD18 glycoproteins. Thus, neutrophil activating factor is a third mediator, in addition to platelet-activating factor and endothelial leukocyte adhesion molecule 1, that is synthesized by activated endothelium and that can induce polymorphonuclear leukocyte adhesion to endothelial cells. Because NAF is released into the pericellular fluid, it may also stimulate binding of the leukocytes to exposed subendothelial structures at sites of vascular injury.

Signalling pathway of tumor necrosis factor in normal and tumor cells

Several aspects of the activity and effects of tumor necrosis factor (TNF) were investigated to gain further insight into its cytotoxic mechanism. The relation between number of TNF receptors and TNF susceptibility of both tumor cells and normal cells was studied, utilizing a specific binding assay. Among the tumor cells, a fairly close correlation (r = 0.855) was observed between receptor number and sensitivity to TNF. No cytotoxic effect by TNF was observed on any of the normal cells tested, even though TNF receptors were shown to be present, and cell proliferation was apparently stimulated by TNF in some cases. TNF internalization and intracellular distribution were studied by pulse-labelling and Percoll density gradient centrifugation. In L-M (murine tumorigenic fibroblasts, highly sensitive to TNF cytotoxicity) cells and HEL (human embryonic lung cells, non-sensitive to TNF cytotoxicity) cells, receptor-bound 125I-labelled recombinant human TNF was rapidly internalized and delivered to lysosomes within 15-30 min, and this was followed by degradation and release into the culture medium. The presence of either a cytoskeletal disrupting agent or a lysosomotropic agent was observed to inhibit the cytotoxic effect of TNF, thus also indicating that TNF internalization, followed by delivery to lysosomes, is essential in the cytolytic mechanism of TNF. As observed by [3H]uridine incorporation, TNF did not affect RNA synthesis in L-R cells (TNF-resistant cell lines derived from L-M cells) and HEL cells, but markedly stimulated (by 3.5 times) RNA synthesis in L-M cells.

Evidence for anion channels in secretory vesicles

Secretory vesicles from bovine neurohypophysis were reconstituted into lipid bilayers. Electrical measurements on the lipid bilayers under voltage clamp demonstrated the presence of channels that are permeable to chloride ions, are blocked by 4,4'-diisothiocyanostilbene-2,2'-disulfonate, and are slightly voltage dependent. When several different membrane fractions were used for the reconstitution, the probability of finding channels correlated with the fraction of secretory vesicle membrane in the membrane fraction, indicating that the secretory vesicles are the source of the channels. The observed anion channel can provide a pathway for the anion transport that has previously been described for secretory vesicles. The secretory vesicle anion channel may play a role in calcium-induced secretion.

Isolated neuronal growth cones from developing rat forebrain possess adenylate cyclase activity which can be augmented by various receptor agonists

Isolated neuronal growth cones from neonatal rat forebrain were found to contain a high specific activity of adenylate cyclase (61 pmol cyclic AMP/min/mg protein) compared to the pelleted starting homogenate (5 pmol cyclic AMP/min/mg protein). Forskolin at 10(-4) M increased adenylate cyclase activity in both the pelleted homogenate and growth cone fraction by 70 and 217 pmol cyclic AMP/min/mg protein, respectively, over basal levels. The incremental effect of forskolin was 3-fold greater in the growth cone fraction than in the pelleted homogenate. However, relative to basal levels in each of the two fractions, forskolin increased adenylate cyclase activity in the growth cone fraction by only approx. 5-fold compared to 15-fold in the pelleted homogenate. Dopamine (10(-4) M), vasoactive intestinal polypeptide (10(-6) M) and isoproterenol (10(-5) M) also augmented adenylate cyclase activity in the two fractions. In the growth cone fraction, dopamine and vasoactive intestinal polypeptide produced a stimulation over basal levels by approx. 20 pmol cyclic AMP/min/mg protein while isoproterenol produced a stimulation of approx. 10 pmol cAMP/min/mg protein. The incremental effects of these receptor agonists in the growth cone fraction are approx. 5-fold greater than in the pelleted homogenate. The dopamine-sensitive adenylate cyclase activity in the growth cone fraction could be blocked by the compound SCH23390, a selective D1 receptor antagonist. At saturating concentrations, all combinations of dopamine, vasoactive intestinal polypeptide and isoproterenol were found to be completely additive on adenylate cyclase activity in the growth cone fraction.(ABSTRACT TRUNCATED AT 250 WORDS)

Killing of Proteus mirabilis by polymorphonuclear leukocyte granule proteins: evidence for species specificity by antimicrobial proteins

Low-molecular-weight (Mr, ca. 3,800) polypeptides containing human defensins HNP-1 and HNP-2 (T. Ganz, M. S. Selsted, D. Szlarek, S. L. Harwig, K. Daher, D. F. Bainton, and R. I. Lehrer, J. Clin. Invest. 76:1427-1434, 1985) prepared in our laboratory from acid extracts of human polymorphonuclear granulocyte granules and purified human defensins were found to exert potent bactericidal action against Proteus mirabilis. The antimicrobial action of the extracts of human polymorphonuclear leukocytes granules against P. mirabilis appears to be due to the presence of the defensins. Because P. mirabilis resists the antimicrobial action of other granule proteins, we interpret the present results to mean that the various antimicrobial proteins display species specificity in their microbicidal action.

Activation of human prorenin by neutrophil elastase

Although about 90% of human renin circulates as inactive prorenin, the mechanism of prorenin activation in vivo is not known. We found that human polymorphonuclear leukocytes (PMN) activate prorenin at a neutral pH. Prorenin was partially purified from human amniotic fluid, and its activation was measured by the release of angiotensin I from sheep angiotensinogen. In control experiments, thermolysin was the standard activator. PMN cells were separated from blood and, after N2 cavitation or degranulation by cytochalasin, were fractionated by differential centrifugation. Elastase and cathepsin G activities were determined with synthetic fluorescent substrates. The activators of prorenin concentrated in the azurophil granules were released by Triton; most of the activation was due to elastase. Elastase, purified from human PMN, activated prorenin completely. The activation by the granular fraction was inhibited 77% by a specific elastase inhibitor in the presence of a detergent, but only 22% by a cathepsin G inhibitor. After inhibition of elastase, the residual activity was inhibited by diisopropylfluorophosphate; thus, it was due to a serine protease(s) such as cathepsin G. We suggest that human renin fully activated by elastase may still contain an N-terminal pentapeptide fragment of the propeptide.

Insulin and alpha 2-macroglobulin-methylamine undergo endocytosis by different mechanisms in rat adipocytes: II. Comparison of intracellular events

A previous ultrastructural study showed that gold-labeled insulin (Au-I) and the non-hormonal ligand gold-labeled alpha-2-macroglobulin-methylamine (Au-alpha 2MGMA) underwent endocytosis by dissimilar cell surface structures on rat adipocytes. The present ultrastructural study compared the intracellular routes taken by these two ligands in adipocytes. Intracellular Au-alpha 2MGMA was initially found within apparent coated vesicles but Au-I was not, consistent with the previous demonstration that Au-alpha 2MGMA underwent endocytosis by coated pits whereas Au-I was internalized by uncoated micropinocytotic invaginations. Early in the endocytic pathway, the two ligands were segregated within separate small vesicles and tubulovesicles. Au-alpha 2MGMA was concentrated in a small number of these structures whereas Au-I was sparsely distributed among a relatively large number. Subsequently, the two endocytic pathways converged as the ligands intermingled within pale multivesicular bodies and lysosome-like structures. Au-I was less efficiently transferred to lysosomes than Au-alpha 2MGMA since a greater proportion of intracellular Au-I remained associated with small vesicles and tubulovesicles. This study indicates that early intracellular events in the endocytic pathways of insulin and alpha 2MGMA are distinct. These findings are discussed in light of the fundamentally dissimilar biological roles of these two molecules and the possible involvement of the endocytic pathway in the insulin signaling mechanism.

Platelet membrane vesicles reduced microvascular bleeding times in thrombocytopenic rabbits

We investigated the possible role of platelet membrane vesicles on hemostatic function in vivo. Platelet membrane vesicles were prepared from rabbit platelets stored for up to 6 months at -65 degrees C and transfused into thrombocytopenic rabbits. Significant reductions in microvascular bleeding times were observed up to 24 hours after transfusion, with the greatest corrections at 4 hours. Measurements of factor V, factor VIII, fibrin degradation products, and fibrinogen in animals transfused with membrane ruled out intravascular coagulation and suggested a direct effect of platelet membrane vesicles at the bleeding sites. This conclusion was supported morphologically by identification of membrane vesicles in bleeding time lesions and radiologically by accumulation of 111In-labeled vesicles in lesions. Production of platelet membrane vesicles was simple, and freezing allowed long-term storage of a product capable of short-term hemostasis.

Functional heterogeneity of periportal and perivenous hepatocytes

Periportal and perivenous hepatocytes differ in their content of many key enzymes and subcellular structures. The cells also receive different regulatory signals due to the gradients established during liver passage of oxygen, substrates and hormones. The signal heterogeneity is important not only for short-term regulation of metabolism but also for long-term control, i.e. the induction of liver cell heterogeneity. The zonal heterogeneity changes upon longer lasting physiological and pathological alterations of the metabolic situation such as starvation, diabetes or regeneration after partial hepatectomy; it develops only gradually during the first weeks of postnatal life. The model of 'metabolic zonation' proposes a functional specialization for the two zones: in the periportal zone oxidative energy metabolism with beta-oxidation and amino acid metabolism, ureagenesis, gluconeogenesis, cholesterol synthesis, bile formation and oxidation protection are the predominant activities, and in the perivenous zone glycolysis, liponeogenesis, ketogenesis, glutamine formation and biotransformation are the prevalent processes.

The role of charge microheterogeneity of basic protein in the formation and maintenance of the multilayered structure of myelin: a possible role in multiple sclerosis

Isolation of several of the charge isomers from both normal and multiple sclerosis (MS) myelin basic protein (MBP) was achieved on CM-52 columns at pH 10.6. In liquid x-ray diffraction and aggregation experiments, corresponding charge isomers were equally effective in the formation of multilayers, demonstrating the dominant role of overall net positive charge. These studies demonstrated that the change in overall charge of MBP of one net positive charge was sufficient to produce large changes in aggregation and in multilayer formation. The x-ray diffraction experiments showed that component 1 was twice as effective as component 2 although they differed in charge by a single positive charge. Component 3 was less effective than component 2 and component "8" was not effective at all. Vesicle aggregation also showed a dependence on net positive charge. In order of decreasing effectiveness, component 1 greater than component 2 greater than component 3 greater than component "8". Since overall charge on MBP is determined by contributions from the various charge isomers, the relative proportions of these charge isomers favoring the less cationic components could explain the observation that MBP from MS victims was less effective than MBP from normal brain in vesicle aggregation and multilayer formation. The isolation of myelin-containing white matter fractions from both normal and MS tissue in which the loss of some of the most cationic charge isomers was correlated with presence of less compact myelin supports this hypothesis.

Effects of the lysosomal fraction of polymorphonuclear leukocytes on proliferation of cultured vascular cells

The effects of the lysosomal fraction isolated from polymorphonuclear leukocytes (PLF) on the growth of cultivated aortic medial smooth muscle cells (SMCs) and arterial endothelial cells (ECs) were studied by assaying DNA synthesis and counting the numbers of cells. PLF proved to promote the growth of cultivated SMCs and ECs. There was a positive correlation between an increase in DNA synthesis and the dose of PLF. The growth-promoting effect was observed in sparsely cultivated SMCs and ECs, in densely cultivated SMCs, but not in confluently cultivated ECs. The difference in response between SMCs and ECs seems to depend on their biological characteristics. Because a small amount of PLF showed potent growth-promoting activity in the presence of 10% fetal bovine serum which possesses a high protease blocking activity, the mechanism of this promoting activity is suggested to be independent of the proteases contained in PLF.

Sexual behavior in Aplysia fasciata induced by homogenates of the distal large hermaphroditic duct

Copulation was induced in pairs of Aplysia fasciata by adding to the environment a homogenate of the distal portion of the large hermaphroditic duct. Similar effects were not observed in response to an abdominal ganglion homogenate. The data suggest that the duct may secrete a pheromone initiating copulation in Aplysia.

Characterization of gonadotropin-sensitive adenylate cyclase activity in human testis: uncoupling of the receptor-cyclase complex by specific hormonal antagonist

Basal and gonadotropin stimulated adenylate cyclase activity was assessed in testicular tissues obtained from men (20-80 years). A disparity was observed in the gonadotropin responsiveness of the human testicular adenylate cyclase system to hFSH and hCG stimulation. Of the tissues analyzed, 61% were FSH responsive and 22% showed low response to hCG. Forskolin, a diterpene which activates adenylate cyclase by a receptor independent mechanism, stimulated adenylate cyclase activity in the gonadotropin unresponsive tissues. This suggests that the tissue unresponsiveness is due to an uncoupling of the catalytic subunit of the adenylate cyclase. Several functional properties of the FSH responsive human testicular adenylate cyclase were investigated. hFSH and oFSH stimulated the enzyme activity in a concentration dependent manner. However, the hormone (DG-oFSH) in which 80% of the carbohydrate residues had been removed was inactive, despite its good binding ability to the FSH receptor. hFSH stimulated adenylate cyclase activity was inhibited by DG-oFSH but not by DG-hCG (deglycosylated hCG). The data demonstrates the existence of specific FSH and LH(hCG) receptors in human testicular membranes. The FSH receptors in some tissues are coupled to adenylate cyclase. The link between the FSH receptor and adenylate cyclase may be uncoupled in the presence of the deglycosylated form of oFSH resulting in a loss of hormone response.

Isolation of neuropeptide-containing vesicles from the guinea pig ileum

Three distinct vesicle fractions enriched 40-60 times in the neuropeptides substance P, somatostatin, and vasoactive intestinal peptide (VIP) were prepared from the myenteric plexus of guinea pig ileum by density gradient centrifugation in a small zonal rotor. Mean densities (in g X ml-1) and diameters (in nm) of the three classes of vesicles were: substance P, 1.123, 65; somatostatin, 1.138, 37; VIP, 1.148, 110; standard deviations were about 5%. These peaks were distinct from the peak of acetylcholine-containing vesicles of density 1.066 g X ml-1 and diameter 61 nm. When a relatively mild method of homogenization was used a second peak of acetylcholine appeared in the same region of the gradient as VIP and the VIP was larger. This may represent a class of vesicles containing both acetylcholine and VIP, though cosedimentation of two classes of vesicles of almost the same density and similar fragility, one containing VIP and the other acetylcholine, cannot be entirely excluded on present evidence.

Characterization of a factor that can prevent random transcription of cloned rDNA and its probable relationship to poly(ADP-ribose) polymerase

A factor which eliminated nonspecific transcription of cloned rat rDNA was extensively purified from rat mammary adenocarcinoma ascites cells by successive fractionations on DEAE-Sephadex and heparin-Sepharose columns. The fractions containing RNA polymerase I (HS-B) and fractions eluting thereafter (HS-C) from the heparin-Sepharose column were pooled separately. Addition of HS-C to HS-B prevented random transcription of rDNA and yielded an accurate rDNA transcript with negligible non-specific transcription. The factor was essentially homogeneous and corresponded to Poly(ADP-ribose) polymerase with respect to molecular weight, dependence on DNA for its activity and its ability to undergo auto ADP-ribosylation. The total amount of protein in the transcription assay was approximately 2 micrograms, which indicates a high degree of purity of all the factors required for specific transcription of rDNA.

Membrane fractionation of canine aortic smooth muscle: subcellular distribution of calcium transport activity

Various subcellular membrane fractions were isolated from dog aortic smooth muscle by conventional differential centrifugation followed by isopycnic centrifugation on a sucrose density gradient. These subcellular fractions were characterized by membrane marker enzyme activities, morphological features and the electrophoretic patterns on a sodium dodecyl sulfate polyacrylamide gel. Our results showed that the microsomal membrane fraction isolated by differential centrifugation was very heterogeneous and contained substantial amount of plasma membranes which could be further enriched as a light density fraction on the sucrose density gradient. The subcellular distribution of Ca2+ binding in the absence of ATP and Ca2+ transport in the presence of ATP closely paralleled the distribution of plasma membrane markers. The ATP-supported Ca2+ transport was inhibited by several Ca2+ ionophores, enhanced by inorganic phosphate and oxalate ions and cosedimented toward higher density in a continuous source density gradient with plasma membrane marker enzyme activity in the presence of digitonin. Our present work strongly suggests that plasma membrane is the predominant component of microsomal fraction and responsible for most, if not all, of the azide-insensitive ATP-supported Ca2+ accumulation.

Cell membrane shape control--effects of chloromethyl ketone peptides

The shape of the human erythrocyte is normally maintained in vivo as a biconcave disc for 120 days. In vitro, the cell shape can be altered readily by amphipathic compounds; however, given time and an energy source, the cells can recover the discoid morphology. An active shape control mechanism is postulated to regulate erythrocyte shape. The shape recovery process is a necessary element in reversing perturbations of shape and is basic to our understanding of how membrane shape is altered. We report here that the process of shape recovery from crenation is dramatically accelerated upon pretreatment of the cells with micromolar (20-100 microM) concentrations of chloromethyl ketone peptides [such as N-alpha-tosyl-L-phenylalanine-chloromethyl ketone (tos-pheCH2Cl)]. Such pretreatments do not appear to affect cellular viability, as judged by their normal biconcave disc shape, their sensitivity to crenators, their lactic acid production, or the ATP-dependent shape change of the purified membranes. Treatment with high concentrations of tos-pheCH2Cl does cause normal cells to become stomatocytic by an energy-requiring process, i.e., it requires glucose, incubation at 37 degrees C, and will not occur in ATP-depleted cells. We suggest that the chloromethyl ketone peptides affect a metabolic process that is associated with the hexose monophosphate (HMP) shunt. Through the alteration of the HMP shunt metabolism, they modify an active stomatocytic process in the erythrocyte that can correct for the perturbation caused by crenators. Implications of these findings for analogous phenomena in cultured cells are discussed.

Light rough endoplasmic reticulum membranes re-appear before heavy rough membranes after feeding starved MPC-11 cells

In 48 hr starved MPC-11 cells smooth (S) endoplasmic reticulum (ER) membranes accounted for more than 80% of the total ER membrane fraction. After 2 1/2 hr feeding the amount of S membranes was reduced to below 55% while light rough (LR) membranes had increased from about 16% of the total to 42%. The percentage of heavy rough (HR) membranes only showed a minor increase during the incubation period. The results show that following an accumulation of S membranes in starved cells the LR membranes 're-appear' more rapidly than the HR membranes. This difference in behaviour provides further support to the concept that LR and HR membranes represent distinct domains of the ER system.

Developmental changes in myocardial mechanical function and subcellular organelles

This study investigates the developmental changes in myocardial mechanical function and the function of subcellular organelles. Mechanical function was determined at various Ca2+ concentrations ( [Ca2+]0) in the isolated, arterially perfused heart of the fetus (28th day of gestation), newborn (3-5 day old), and adult rabbit. Maximal force of contraction in the fetus (observed at 7.5 mM [Ca2+]0) was significantly less than that in the newborn (observed at 30 mM ( [Ca2+]0), and both the fetus and newborn values were significantly less than that in the adult (observed at 15 mM [Ca2+]0). The myofibrillar content in the fetus and ATPase activity in the fetus and newborn were significantly less than in the adult at pCa 4 and 5 where this enzyme was maximally activated. Both the amount of sarcoplasmic reticulum (SR) and SR Ca2+ uptake per gram of muscle increased with age. Mitochondrial Ca2+ uptake was not observed at pCa more than 6 (physiological range) in all age groups. At pCa less than 6, mitochondrial Ca2+ uptake (per g muscle) in the newborn was significantly greater than in the fetus and adult. Ca2+ uptake by crude homogenate in the newborn was also greater than in the fetus and adult. These data suggest that the age-related change in myocardial contractility is due to the differences in intracellular Ca2+ concentration and myofibrillar content as well as ATPase activity. Intracellular Ca2+ concentration may vary with development depending on the relative capability of Ca2+-releasing system and Ca2+-sequestering system.