Biomedical subjects

E Arzt

Publications and source records attributed to E Arzt.

At least 55 records · Page 3Linked to original sources

PubMed1996

Molecular and functional evidence for in vitro cytokine enhancement of human and murine target cell sensitivity to glucocorticoids. TNF-alpha priming increases glucocorticoid inhibition of TNF-alpha-induced cytotoxicity/apoptosis.

Cytokine-induced glucocorticoid secretion and glucocorticoid inhibition of cytokine synthesis and pleiotropic actions act as important safeguards in preventing cytokine overreaction. We found that TNF-alpha increased glucocorticoid-induced transcriptional activity of the glucocorticoid receptor (GR) via the glucocorticoid response elements (GRE) in L-929 mouse fibroblasts transfected with a glucocorticoid-inducible reporter plasmid. In addition, TNF-alpha also enhanced GR number. The TNF-alpha effect on transcriptional activity was absent in other cell lines that express TNF-alpha receptors but not GRs, and became manifest when a GR expression vector was cotransfected, indicating that TNF-alpha, independent of any effect it may have on GR number, has a stimulatory effect on the glucocorticoid-induced transcriptional activity of the GR. Moreover, TNF-alpha increased GR binding to GRE. As a functional biological correlate of this mechanism, priming of L-929 cells with a low (noncytotoxic) dose of TNF-alpha significantly increased the sensitivity to glucocorticoid inhibition of TNF-alpha-induced cytotoxicity/apoptosis. TNF-alpha and IL-1 beta had the same stimulatory action on glucocorticoid-induced transcriptional activity of the GR via the GRE, in different types of cytokine/glucocorticoid target cells (glioma, pituitary, epithelioid). The phenomenon may therefore reflect a general molecular mechanism whereby cytokines modulate the transcriptional activity of the GR, thus potentiating the counterregulation by glucocorticoids at the level of their target cells.

Animals↗

PubMed1996

Inhibition of lipopolysaccharide-induced monocyte interleukin-1 receptor antagonist synthesis by cortisol: involvement of the mineralocorticoid receptor.

Glucocorticoids, as a part of their physiological role in the control of inflammatory and immune processes, suppress the expression of interleukin-1 (IL-1) and other cytokines. Human monocyte IL-1 receptor antagonist (IL-1ra) messenger ribonucleic acid (mRNA) expression and protein secretion are inhibited by dexamethasone. We have now further studied the regulation of IL-1ra by the major physiological human glucocorticoid, cortisol. We found that cortisol incubation induced a decrease in IL-1ra mRNA expression and a significant inhibition of IL-1ra protein secretion in cell cultures of human peripheral monocytes stimulated with the bacterial endotoxin lipopolysaccharide (LPS). Oral administration of 276 mumol cortisol to normal subjects also decreased LPS-induced IL-1ra synthesis in cultured monocytes. By coincubating the monocytes with either the mineralocorticoid antagonist spironolactone or the glucocorticoid receptor antagonist RU 38486, the in vitro cortisol-induced inhibition of LPS-stimulated IL-1ra secretion was partially reversed. The mineralocorticoid aldosterone exerted a significant decrease in LPS-induced monocyte IL-1ra secretion in vitro, which was blocked by coincubation with spironolactone. In addition, the expression of mineralocorticoid receptor mRNA in human monocytes was observed by PCR of reversed transcribed RNA. Our results further indicate that corticosteroids physiologically control the IL-1/IL-1ra system during inflammatory or immune processes. Moreover, we provide evidence that, in addition to a glucocorticoid receptor-mediated effect, the mineralocorticoid receptor is involved in the inhibition of monocyte IL-1ra secretion by cortisol.

Adult↗

PubMed1996

Autocrine and paracrine roles of polypeptide growth factors, cytokines and vasogenic substances in normal and tumorous pituitary function and growth: a review.

In addition to the classical hormones, the production of numerous polypeptide growth factors, cytokines, vasogenic substances and neuropeptides by pituitary cells has been demonstrated. Expression of the corresponding receptors on pituitary cells enables these factors to influence growth and function of the pituitary by auto- or paracrine mechanisms. Thus, in addition to the external endocrine control of pituitary growth and function, an intrinsic intercellular communication network seems to be involved in the control of pituitary homeostasis. The cell-to-cell communication may be of importance for the pre- and postnatal differentiation of the pituitary, for the regulation of the cellular composition of the gland (by balancing mitosis and apoptosis and controlling angiogenesis) and for the adaption of pituitary function to altered physiological conditions (i.e. stress, pregnancy and diseases). Differences in the expression of or the response to the above-mentioned factors in pituitary adenomas indicate that these substances are of importance for pituitary tumorigenesis. Disturbances of auto-/paracrine mechanisms may not necessarily be involved in the tumor initiation processes, but they may play a crucial role in tumor progression. After the initial transformation, the clonal expansion of the tumor cell is dependent on its ability to escape either from the inhibitory action of growth suppressing factors or to develop an autocrine mechanism that allows autonomous growth. In summary, therefore, this review outlines the potential role of polypeptide growth factors, cytokines and vasogenic peptides as auto-/paracrine-acting substances in normal pituitary and pituitary adenomas.

Animals↗

PubMed1995

TRH receptor on immune cells: in vitro and in vivo stimulation of human lymphocyte and rat splenocyte DNA synthesis by TRH.

This work examined whether (1) immune cells express thyrotrophin releasing hormone (TRH) receptor mRNA and (2) TRH modulates lymphocyte activation. By Northern blot of RNA extracted from human peripheral blood mononuclear cells (PBMC) and rat splenocytes, a single TRH receptor mRNA band of about 3.8 kb (identical to that obtained from pituitary cells) was obtained, under both basal and stimulated conditions. A significant increase in DNA synthesis was observed in phytohemagglutinin-stimulated PBMC and concanavalin A (Con A) stimulated splenocytes when TRH (10(-6) M-10(-12) M) was added. After 5, 30, 60, 180 min and 24 h of TRH administration in vivo, a significant increase in the rat splenocyte proliferative response to Con A was observed. In vivo administration of anti-rat TSH antibody (1/1000) blocked the increase observed after 30 min of TRH administration on the Con A stimulated splenocyte response. TRH possess immunostimulatory functions directly via its receptor and indirectly via release of other immunostimulatory factors such as thyrotrophin.

Animals↗

PubMed1995

The glucocorticoid sensitivity of lymphocytes changes according to the activity of the hypothalamic-pituitary-adrenocortical system.

Cortisol inhibition of phytohemagglutinin (PHA)-induced lymphocyte activation was studied in vitro in peripheral blood mononuclear cells (PBMC) of patients with pathologies of the hypothalamic-pituitary-adrenocortical (HPA) system (n = 18) as well as in students under and out of academic stress. In patients with HPA pathologies, cortisol-induced inhibition of lymphocyte interleukin-2 (IL-2) secretion in vitro positively correlated (p < .005) with IL-2 synthesis, such that lymphocytes secreting less IL-2 were less cortisol sensitive. Similarly, in stressed students there was a positive correlation (p < .02) between lymphocyte DNA synthesis and cortisol inhibition in vitro. Academic stress also resulted in a decrease (p < .01) of lymphocyte cortisol sensitivity. The same tendency was observed in patients with Cushing's syndrome when compared with hypocortisolemic patients. Normal controls whose lymphocytes were glucocorticoid resistant showed higher lymphocyte activation than glucocorticoid sensitive subjects. This pattern of glucocorticoid sensitivity was reversed in individuals with abnormal glucocorticoid secretion due to HPA pathology or stress.

Adult↗

PubMed1995

Corticotropin-releasing hormone differentially modulates the interleukin-1 system according to the level of monocyte activation by endotoxin.

The interleukin-1 (IL-1) system is constituted by IL-1 alpha and IL-1 beta and IL-1 receptor antagonist (IL-1ra) that bind the same IL-1 receptors. Hypothalamic-pituitary-adrenal axis hormones are major mediators of the neuroendocrine control over immune function. Corticotropin-releasing hormone (CRH) is produced in peripheral inflammatory sites; its direct effects on inflammatory cytokine synthesis, however, remain unclear. We have studied the effects of CRH (0.1-100 nM) on IL-1 beta and IL-1ra expression by human peripheral monocytes in culture activated with different doses of lipopolysaccharide (LPS). In the absence of LPS, CRH up-regulated IL-1ra and IL-1 beta messenger RNA expression as well as protein synthesis. No significant changes were observed with low doses of LPS (1 ng/ml). In contrast, in combination with high doses of LPS (1 microgram/ml), CRH caused inhibition of IL-1ra and IL-1 beta transcription and secretion. The CRH effects were blocked by its antagonist alpha-helical CRH and mediated by intracellular cAMP. These data indicate that CRH modulates the IL-1 system; depending on the state of activation of the monocyte, CRH exerts an inhibitory control on the activated cell and a stimulatory action on the resting monocyte.

Cells, Cultured↗

PubMed1995

Long-term intracerebroventricular corticotropin-releasing hormone administration induces distinct changes in rat splenocyte activation and cytokine expression.

The effects of long-term corticotropin-releasing hormone (CRH) infusion in the lateral ventricle of the rat on hypothalamic-pituitary-adrenocortical (HPA) axis parameters and on the immune system function were studied. Compared with infusion of vehicle, the CRH treatment produced a sustained overactivity of the HPA axis, as evidenced by elevated plasma ACTH and corticosterone levels, increased anterior pituitary POMC messenger RNA (mRNA) expression, and adrenal enlargement. Long-term CRH treatment also inhibited body weight gain and reduced thymus and spleen weight. In the CRH-treated animals, both Concanavalin A (Con A)-induced T lymphocyte proliferation and lipopolysaccharide (LPS)-induced B lymphocyte mitogenesis was largely suppressed. Surprisingly, interleukin-2 (IL-2) levels were higher in supernatants of splenocyte cultures from CRH-treated rats than in those of control animals. However, IL-2 receptor alpha chain (IL-2R alpha) mRNA expression after Con A stimulation was highly suppressed in the CRH-treated animals. In addition, Northern blot analysis of RNA from splenocytes isolated from spleens of CRH-treated rats revealed a marked expression of IL-1 beta mRNA, in contrast to the barely detectable levels of this cytokine in control animals. Moreover, incubation of total splenocytes and spleen macrophages with LPS resulted in an enhanced induction of IL-1 beta mRNA in cells of CRH-treated rats compared with that of control animals. When adrenalectomized rats were treated with CRH or vehicle, the effects of the CRH treatment on T and B cell proliferation, IL-2 production, and IL-1 beta mRNA expression were abolished. Thus, a continuously increased HPA axis drive results in disparate changes in immune system function. Whether the observed changes in cytokine expression should be regarded as physiologically adaptive adjustments in support of immune function or as potentially pathological anomalies remains to be elucidated.

Animals↗

PubMed1995

Involvement of interleukin-1 and interleukin-1 receptor antagonist in rat pituitary cell growth regulation.

Interleukin-1 (IL-1), one of the mediators of the interaction between the immune and the neuroendocrine system, is well known to modulate anterior pituitary hormone secretion. As IL-1 influences growth of various cell types, we investigated whether IL-1 is also a growth factor of pituitary cells. We demonstrate that IL-1 dose and time dependently inhibits the growth of normal rat pituitary cells under serum-free conditions. The inhibitory potencies of IL-1 alpha (ED50, 8 pg/ml) and IL-1 beta (ED50, 6 pg/ml) were nearly identical. In the presence of low amounts of serum, both IL-1 alpha (ED50, 130 pg/ml) and IL-1 beta (ED50, 90 pg/ml) were less effective in inhibiting growth. The IL-1-induced growth inhibition was IL-1 receptor mediated, because both IL-1 alpha- and IL-1 beta-mediated growth suppression could be completely reversed by the IL-1 receptor antagonist, the physiological counterpart of IL-1. In the mammosomatotroph GH3 rat pituitary tumor cell line, IL-1 failed to influence growth, indicating that either IL-1 receptors are missing or the IL-1 signaling pathway is uncoupled from the growth regulation. In contrast to growth, in our rat pituitary monolayer cell culture system, IL-1 did not affect ACTH, GH, or PRL secretion as described previously. This discrepancy suggests the involvement of different mechanisms in the IL-1-induced mediation of growth and hormone secretion.

Adrenocorticotropic Hormone↗

PubMed1994

Involvement of the estrogen receptor in the growth response of pituitary tumor cells to interleukin-2.

Having recently demonstrated in separate studies that the T-cell cytokine, interleukin-2, induces the growth of the pituitary tumor cell line GH3 and that in the same cells, the estrogen receptor mediates the mitogenic effect of growth factors, we sought here to determine whether the estrogen receptor was involved in the response to interleukin-2. We demonstrate that under steroid and serum free growth conditions, the pure antiestrogen, ZM 182780, blocks the mitogenic response of GH3 cells to interleukin-2. Transfection studies with a reporter plasmid responsive to the transcriptionally active estrogen receptor show that even in the absence of ligand, the estrogen receptor in these cells is transcriptionally active and this can be increased by interleukin-2. Further studies on the two estrogen receptor regulated proteins, the progesterone receptor and prolactin, showing that the levels of these proteins were increased by exposure of cells to interleukin-2, support the idea of a cross-talk between the estrogen receptor and interleukin-2 signal transduction.

Animals↗

PubMed1994

Inhibition of interleukin-2-mediated lymphocyte activation in patients with Cushing's syndrome: a comparison with hypocortisolemic patients.

We investigated the lymphocyte interleukin-2 (IL-2) system, which is critically involved in lymphocyte activation, in patients with disorders or the hypothalamic-pituitary-adrenal (HPA) axis. Patients with Cushing's syndrome (n = 9) showed a significant (p < 0.05) inhibition of phytohemagglutinin (PHA)-stimulated IL-2 secretion by peripheral lymphocytes and a decrease of sensitivity to cortisol inhibition in vitro compared to normal subjects (n = 9). Circulating soluble interleukin-2 receptor (sIL-2R) levels were significantly decreased (p < 0.05), whereas no significant difference was observed in PHA-induced sIL-2R release in vitro. In patients with hypocortisolism (n = 12), in vitro IL-2 synthesis was increased compared to normal subjects and to patients with Cushing's syndrome (p < 0.01). In vitro sIL-2R release was significantly higher (p < 0.01) compared to patients with Cushing's syndrome. In contrast to patients with secondary adrenal insufficiency (n = 7), patients with an adrenal origin of hypocortisolism (Addison's disease, bilateral adrenalectomy; n = 5) showed significantly elevated circulating sIL-2R levels compared to normal subjects and patients with Cushing's syndrome (p < 0.005). There was no significant difference between the study groups in mitogen-induced DNA synthesis. This is the first description of alterations of cytokine secretion in patients with HPA axis disorders. The contrary effects of long-term hypercortisolism and insufficient or absent adrenal glucocorticoid secretion on IL-2-mediated lymphocyte activation could account for the immune states previously observed in these patients.

Adult↗

PubMed1994

Prenatal immune challenge alters the hypothalamic-pituitary-adrenocortical axis in adult rats.

We investigated whether non-abortive maternal infections would compromise fetal brain development and alter hypothalamic-pituitary-adrenocortical (HPA) axis functioning when adult. To study putative teratogenic effects of a T cell-mediated immune response versus an endotoxic challenge, 10-d-pregnant rats received a single intraperitoneal injection of 5 x 10(8) human red blood cells (HRBC) or gram-negative bacterial endotoxin (Escherichia coli LPS: 30 micrograms/kg). The adult male progeny (3 mo old) of both experimental groups showed increased basal plasma corticosterone levels. In addition, after novelty stress the HRBC group, but not the LPS group, showed increased ACTH and corticosterone levels. Both groups showed substantial decreases in mineralocorticoid (MR) and glucocorticoid receptor (GR) levels in the hippocampus, a limbic brain structure critical for HPA axis regulation, whereas GR concentrations in the hypothalamus were unchanged and in anterior pituitary were slightly increased. HRBC and LPS indeed stimulated the maternal immune system as revealed by specific anti-HRBC antibody production and enhanced IL-1 beta mRNA expression in splenocytes, respectively. This study demonstrates that a T cell-mediated immune response as well as an endotoxic challenge during pregnancy can induce anomalies in HPA axis function in adulthood. Clinically, it may be postulated that disturbed fetal brain development due to prenatal immune challenge increases the vulnerability to develop mental illness involving inadequate responses to stress.

Animals↗

PubMed1994

Glucocorticoids suppress interleukin-1 receptor antagonist synthesis following induction by endotoxin.

Glucocorticoids, as part of their physiological role in the control of inflammatory and immune processes, suppress the expression of IL-1 and other cytokines. We have found a dose-dependent inhibition by dexamethasone (10 nM to 10 microM) of mRNA levels of the recently cloned IL-1 receptor antagonist (IL-1ra) in endotoxin-stimulated human monocytes. At the same concentrations, both dexamethasone and cortisol inhibited the secretion of IL-1ra. These inhibitory effects were reversed by blocking glucocorticoid receptors with the specific antagonist RU 38486, but not by adding exogenous IL-1, even up to 100 ng/ml, to the monocytes. A similar inhibition of IL-1ra mRNA and protein secretion was found in monocytes obtained after dexamethasone administration in vivo. In addition, we observed parallel increases in glucocorticoid and IL-1ra levels following endotoxin administration to normal volunteers. Our results show that glucocorticoids shut down not only IL-1 but also IL-1ra expression, ruling out induction of IL-1ra as part of the glucocorticoid antiinflammatory mechanism. The control of the delicate immunoregulatory balance of the IL-1/IL-1ra system during endotoxemia underscores the physiological importance of glucocorticoids in the final control of immune responses.

Adult↗

PubMed1994

Expression of interleukin-1 receptor antagonist in human pituitary adenomas in vitro.

The production of cytokines and their receptors in the pituitary gland as well as receptor-mediated cytokine effects on pituitary function have been demonstrated. We have investigated whether the naturally occurring interleukin-1 receptor antagonist (IL-1ra), which has been shown to block IL-1 biological actions during inflammatory processes, could be expressed in human pituitary adenomas (n = 16) cultured in vitro. By polymerase chain reaction of reverse-transcribed RNA we detected IL-1ra messenger RNA in cultures of all types of pituitary adenomas under basal conditions as well as after stimulation of the cells with endotoxin or phorbol myristate acetate. The amplified complementary DNA fragment was identical to the fragment observed when RNA from purified human monocytes was subjected to reverse transcription polymerase chain reaction. In addition, we provide evidence that the IL-1ra messenger RNA detected in human pituitary adenomas corresponds to the intracellular IL-1ra variant. By using specific primers for the monocyte/macrophage marker CD14 as a control, we could exclude a contamination by monocytes or macrophages in the cell cultures of pituitary adenomas as a source of IL-1ra expression. Immunofluorescence studies showed the presence of cellular IL-1ra protein in the pituitary adenoma cultures and the colocalization with hormone-producing cells in GH- and ACTH-secreting adenomas. Production of IL-1ra within the anterior pituitary may act as a protective mechanism, modulating the sensitivity of pituitary cells to circulating or intrinsically produced IL-1 during inflammatory or tumoral processes.

Adenoma↗

PubMed1993

Low lymphocyte interferon-gamma production and variable proliferative response in anorexia nervosa patients.

Interferon-gamma (IFN-gamma) production by peripheral blood mononuclear cells (PBMC) in 14 patients with anorexia nervosa (AN) was significantly lower than in 14 age-matched healthy controls. Follow-up samples in four patients displayed low levels, except in two when they recovered the IFN-gamma production as the hormonal cycles were restored. A large interindividual variation for the lymphocyte proliferative response was observed in 30 AN patients. DNA synthesis of PBMC was normal in 8 patients (27%), significantly increased in 6 (20%) (P < 0.001), and significantly decreased in 16 (53%) (P < 0.001). IFN-gamma inhibition was reversed by culturing a control lymphocyte population with monocytes from patients with AN. This was not observed in cultures of control monocytes and AN lymphocytes. IL-2 receptor (TAC subunit) was assessed and no difference was found in the number of TAC-positive cells between patients and controls. These results point out impaired production of the immunomodulator cytokine IFN-gamma as a major functional defect of AN peripheral lymphocytes.

Adolescent↗

PubMed1993

Superinduction of mitogen-stimulated interferon-gamma production and other lymphokines by Sendai virus.

We observed that Sendai virus preinduction of peripheral blood mononuclear cells and subsequent mitogenic stimulation resulted in: (i) Superproduction of interferon-gamma, (IFN-gamma) (ii) an increase in interleukin-2 (IL-2) synthesis that correlates with DNA synthesis when stimulated with phytohemagglutinin (PHA) or pokeweed mitogen (PWM) after treatment with the Sendai virus, while stimulation with Protein A from Staphylococcus aureus was not affected, and (iii) enhanced tumor necrosis factor-alpha (TNF-alpha) production in response to bacterial lipopolysaccharide (LPS). Treatment of monocyte cultures with LPS and cycloheximide or actinomycin-D inhibited the superinduction phenomenon. When cycloheximide was added at the viral induction time, the inhibition of TNF-alpha superproduction and DNA synthesis was still observed. These results suggest that Sendai virus lymphocyte superinduction is specific for a particular stimulatory pathway, not dependent on mRNA accumulation, and probably mediated by induction of an activating protein.

CD4-CD8 Ratio↗

PubMed1993

Secretion of polypeptide growth factors by human nonfunctioning pituitary adenoma cells in culture.

The growth-promoting activities of tumor-conditioned media (TU-CM) obtained from 23 cultured human nonfunctioning pituitary adenomas were studied in vitro. TU-CM obtained from adenoma cell cultures increased both cell counts (range: 108-179%; control = growth in serum-free medium = 100%) and 3H-thymidine incorporation (112-139%) of rat pituitary cell cultures, indicating that TU-CM contains growth-stimulating substances. TU-CM was also able to stimulate the growth of normal fibroblasts (3H-thymidine incorporation: 164-178%; cell counts: 145-157%) and endothelial cells (3H-thymidine incorporation: 131-149%; cell counts: 181-217%), suggesting the presence of - possibly angiogenic-growth factors that act on these cell types. However, the growth of hormone-producing cells was also stimulated, since TU-CM increased 3H-thymidine incorporation into rat pituitary cells in the presence of D-Val-MEM, a medium specifically inhibiting growth of fibroblasts. Addition of neutralizing antibodies against transforming growth factor alpha (TGF-alpha), epidermal growth factor (EGF), insulin-like growth factor I (IGF-I) and basic fibroblast growth factor (bFGF), either alone or in different combinations, reduced the growth-promoting activity of TU-CM on rat pituitary cells (range: 96-71%; control = growth effect of TU-CM without antibodies = 100%), strongly indicating the presence of these growth factors in TU-CM. All 4 antibodies together completely inhibited the growth-stimulatory activity of TU-CM, strongly suggesting that these growth factors play the major role among growth-stimulating substances in TU-CM. This is the first study giving evidence that TGF-alpha, EGF, IGF-I and bFGF are secreted by nonfunctioning adenoma cells indicating that the growth factors could be involved in growth regulation of pituitary adenomas by paracrine or autocrine mechanisms.

Adenoma↗

PubMed1993

Interleukin involvement in anterior pituitary cell growth regulation: effects of IL-2 and IL-6.

The pituitary gland plays a central role in the interactions between the immune and neuroendocrine systems. The expression of receptors for interleukin-1 (IL-1), IL-2, and IL-6 and the intrinsic production of these ILs by pituitary cells have been described. Previous studies have focused on the way cytokines influence hormone secretion. We have determined whether, in addition to these effects, ILs could affect pituitary cell proliferation. In GH3 cells, both IL-2 (1-100 U/ml) and IL-6 (10-500 U/ml) significantly stimulated [3H]thymidine incorporation and cell count. In contrast, inhibitory effects of both IL-2 and IL-6 at the same concentrations were observed on normal rat anterior pituitary cell growth. This finding was clearly evident when cells were cultured in Minimum Essential Medium-D-valine medium, a condition that results in cultures virtually free of fibroblasts. Autoradiographic studies confirmed that [3H]thymidine was only incorporated in the nucleus of nonfibroblastic pituitary cells. No direct correlation between the effects of IL-2 and IL-6 on cell growth and hormone secretion was apparent. By immunofluorescence, we observed IL-2 receptor expression on GH3 cells and, for the normal rat cultures, a high percentage of PRL-secreting and a lower percentage of GH-producing cells expressing IL-2 receptors, providing new evidence for a direct site of action of IL-2 on pituitary cells. Considering that uncontrolled division of cells may result from either excessive growth stimulation or deficient growth inhibition, the regulation of pituitary cell growth by IL-2 and IL-6 together with their intrinsic pituitary production could be of potential importance in pituitary adenoma pathogenesis.

Animals↗

PubMed1992

Nigericin forms highly stable complexes with lithium and cesium.

Nigericin is a monocarboxylic polyether molecule described as a mobile K+ ionophore unable to transport Li+ and Cs+ across natural or artificial membranes. This paper shows that the ion carrier molecule forms complexes of equivalent energy demands with Li+, Cs+, Na+, Rb+, and K+. This is in accordance with the similar values of the complex stability constants obtained from nigericin with the five alkali metal cations assayed. On the other hand, nigericin-alkali metal cation binding isotherms show faster rates for Li+ and Cs+ than for Na+, K+, and Rb+, in conditions where the carboxylic proton does not dissociate. Furthermore, proton NMR spectra of nigericin-Li+ and nigericin-Cs+ complexes show wide broadenings, suggesting strong cation interaction with the ionophore; in contrast, the complexes with Na+, K+, and Rb+ show only clear-cut chemical shifts. These latter results support the view that nigericin forms highly stable complexes with Li+ and Cs+ and contribute to the explanation for the inability of this ionophore to transport the former cations in conditions where it catalyzes a fast transport of K+ greater than Rb+ greater than Na+.

Biological Transport↗