Cyclic AMP and growth of fibroblasts: effect of environmental pH

On the importance of cAMP and Ca++ in mandibular condylar growth and adaptation

The origin of the mandibular condylar cartilage is not periosteal, like that of the other secondary cartilages; this cartilage originates in a cellular blastema of its own. Despite the fact that the development of secondary cartilages, in general, is dependent on mechanical irritation, that of the condylar cartilage is not. The low level of function experienced postnatally seems to favor growth, but because the proliferation cells of the condylar cartilage are multipotential, they switch their differentiation pathway in the direction of osteoblasts in the absence of function, and growth of the cartilage ceases. This regulation of differentiation is mediated by maturation of the cartilage cells. If function is not present, maturation advances rapidly, and the mature cartilage induces bone formation instead of cartilage. Cyclic AMP and Ca are important mediators in this process, because they affect the advancement of maturation.

Hydrogen ion dynamics and cancer: an appraisal

The concentration of hydrogen ions plays a critical role in all biochemical processes, including multiple enzymatic reactions, and in the regulation of metabolism. The acid-base aspects of metabolism as applied to cancer are considered. Preliminary data are presented. The primary concept of hydrogen ion dynamics is related to prevention, development, and etiology of carcinogenicity, as well as to the regression of certain malignant malignant tumors. The present overview summarizes, in terms of H+ dynamics, many related concepts in oncologic research and associates and integrates a variety of basic and clinical observations toward better understanding of cancer cell behavior, biology, and host-tumor relationships.

Effects of prazosin on the cAMP system in the spontaneously hypertensive rat (SHR) aorta

3',5'-adenosine monophosphate (cAMP), adenylate cyclase and cAMP-phosphodiesterase (PDE) activity were measured in aorta homogenates from normal and spontaneously hypertensive rats (SHR) during treatment with prazosin, an antihypertensive drug. cAMP levels were lower in SHR than in normal rats. In SHR prazosin treatment induced marked inhibition of PDE activity thus causing an increase in cAMP levels; adenylate cyclase activity remained unaffected. This effect was only present for the first 32 days of drug administration.

Identification of a distinct phase during melanogenesis that is sensitive to extracellular pH and ionic strength

The cell line B16/C3 will undergo melanogenesis at a specific time after plating. We have found that this time can be modulated by varying the pH of the culture medium. At high pH levels (8.2--8.6) the onset of melanogenesis occurs in 3 or 4 days, while at lower pH (6.7--7.2) it occurs in 7 or 8 days. Furthermore, the time of onset is also sensitive to the extracellular ionic strength. The addition of sodium lactate, sodium chloride, or any other salt tested delays or blocks completely the onset of melanogenesis. These effects are not simply consequence of growth inhibition, nor can they be correlated with patterns of lactate acccumulation. These cells are sensitive to pH or ionic strength after entering the stationary phase just prior to the time of onset of melanogenesis. The existence of a specific pH-and ionic-strength-sensitive phase may provide an important clue to the events responsible for differentiation in this system.

The effect of medium pH on rate of growth, neurite formation and acetylcholinesterase activity in mouse neuroblastoma cells in culture

Cell division, neurite formation and acetylcholinesterase activity were examined in a clone (NBA2) of mouse neuroblastoma cells maintained for up to 120 hours in medium with pH values between 6.6 and 8.0. Growth rate decreased as pH was reduced from 7.8 to 6.6. Generation time at pH 7.4 was 25 hours, while the rate of cell division was negligible at pH 6.6. The total number of cells at stationary phase was less at the lower pH values. Neurite formation was enhanced markedly as the pH was reduced from 7.4 to 6.6. Acetylcholinesterase activity was 5- to 8-fold greater in cells exposed to medium at pH 6.6 than in cells maintained in medium at pH 7.4. The reduction in the rate of cell division and increases in neurite formation and acetylcholinesterase activity at pH 6.6 were reversible upon exposure of the cells to pH 7.4 medium. Cell viability was greater than 90% at all medium pH values over a period of 120 hours. Uncloned T-59 mouse neuroblastoma cells were affected similarly by changes in pH. These results show that manipulation of the environmental pH can reversibly alter growth, neurite formation, and acetylcholinesterase activity of mouse neuroblastoma cells in culture.

Cyclic AMP and serum arrest of the mitotic activity of human diploid fibroblasts

Mitotic activity in confluent cultures of human diploid fibroblasts was arrested by the reduction of the serum concentration of the incubation medium to 0.5% or by the addition of 0.5 mM 6-N, 2'-O-dibutyryl-adenosine 3':5'-cyclic monophosphate (db cAMP). Under either of these conditions, cultures maintained a constant cell number for 14 days; cultures continuously exposed to medium containing 10% serum doubled their cell number during this 14-day period. The protein cotent per cell decreased by 20% when cells were maintained with 0.5% serum whereas that of cells exposed to db cAMP remained constant. Ultrastructural studies revealed that cells exposed to db cAMP exhibited a morphology typical of cells cultures with 10% serum alone, whereas cells incubated with 0.5% serum showed the ultrastructural changes in mitochondria, endoplasmic reticulum and Golgi complex previously identified with low-serum arrest. Cellular adenosine 3':5'-cyclic monophosphate (cAMP) levels remained constant during the 7-day growth period in which confluency was attained, as well as during the 14-day arrested period with 0.5% serum. These results indicated that the mitotic inhibition induced by reducing the serum concentration of the incubation medium was not mediated by increased intracellular levels of cAMP and differed from that induced by the addition of exogenous db cAMP.

Regulation of growth and morphological modulation of HeLa65 cells in monolayer culture by dibutyryl cyclic AMP, butyrate and their analogs

N6-O2'-Dibutyryl adenosine-3',5' monophosphate (DBcAMP) markedly altered the morphology of HeLa cells by increasing average cell size with an increase in total cell protein and RNA. Such effects were not caused by adenosine 3',5' monophosphate (cAMP) or related nucleosides and nucleotides. Butyrate, an enzyme catalyzed hydrolysis product of DBcAMP, induced a jagged spindle shape in HeLa cells within 8 hours and then caused them to enlarge and resemble those grown with DBcAMP. These effects were specific for butyrate (C4) and pentanoate (C5) and were not observed with isomers, substituted analogs, or other fatty acid derivatives. These morphological effects were prevented by blocking protein synthesis or by altering the cytoskeleton with Colcemide or cytochalasin B.

Hypoxia in fibroblast cultures. I. Changes in glucose consumption by 5 vol.-% oxygen concentration and reduced pH

In secondary cultures of rat embryonic fibroblasts the glucose consumption and lactate concentration were comparatively investigated in 5 and 21 Vol.-% O2 environment at pH 6.6 and pH 7.4 (HEPES-buffer). The results were correlated with cell density. The following observations were made: 1. At pH 6.6 the rate of cell proliferation was reduced to 81%; by additional hypoxia it was reduced to 71%. 2. Increase in cell density effectuated decrease of glucose consumption and lactate production at pH 7.4 and pH 6.6 in 5% as well as in 21% O2 environment. 3. At pH 7.4 enhancement of glucose consumption and lactate production due to hypoxia can be observed only at low cell density. 4. At pH 6.6 respiration of fibroblasts was little influenced by 5% O2 environment. 5. Transition from pH 7.4/21% O2 to pH 6.6/5% O2 effectuated decrease in glucose consumption and lactate concentration in tissues in hypoxic environment. This suggests a pH-governed feedback mechanism. Abbreviations used in the text: c-AMP = cyclic adenosine monophosphate; MPS = acid mucopolysaccharides (glycosaminoglycans).

Adenosine 3': 5'-cyclic monophosphate in young and senescent human fibroblasts during growth and stationary phase in vitro. Effects of prostaglandine E1 and of adrenaline

Cyclic AMP levels per mg of cell protein were higher in late-passage (senescent) fibroblasts than in early-passage (young) fibroblasts both during growth and stationary phase, but, because the protein concentration per unit volume in senescent cells was lower than in young cells, the molar concentrations of intracellular cyclic AMP were very similar in the two cell types. In both young and senescent fibroblasts cyclic AMP levels declined during growth and no increase in intracellular cyclic AMP occurred in association with density-dependent inhibition of growth. These results indicate that changes in cyclic AMP concentration do not play a role in controlling the growth or in the senescent decline of human fibroblasts. Prostaglandin E(1) (1mum) caused maximal increases in fibroblast cyclic AMP concentration of 60-500-fold after 10-30min, and adrenaline (epinephrine) (10mum) caused maximum increases of 5-25-fold after 2-10min, depending on both the number of passages and the period after subculture. The cyclic AMP level in confluent young cells increased more with prostaglandin E(1) and far less with adrenaline than the cyclic AMP level in confluent senescent cells. During growth to confluence the cyclic AMP response to adrenaline declined in young cells and increased in senescent cells. As these responses to prostaglandin E(1) and to adrenaline changed independently of each other and of the basal cyclic AMP concentration, it is suggested that the expression of hormone receptors is altered both during growth to confluence and during senescence of human fibroblasts.

Myosin is a component of the cell surface of cultured cells

Antisera to myosin from mouse L929 cells, mouse uterus, and rabbit skeletal muscle have been prepared in goats. Each antiserum shows specific reaction by immunodiffusion only to the myosin against which it was prepared. Antiserum against L cell myosin agglutinates L929 cells and shows surface localization in unfixed cells by indirect immunofluorescence. This reaction is prevented by immunoabsorption with L cell myosin, but not by absorption with mouse uterine or rabbit skeletal muscle myosins. Elution of the antibody from L cell myosin antiserum that absorbs to fixed L cells yields antibody reactive to L cell myosin in immunodiffusion. At the ultrastructural level, surface localization is also evident with a peroxidase bridge immunocytologic method as a uniform distribution of surface label. Antiserum against L cell myosin also shows localization on the surface of other cells of rodent origin (3T3-4, NRK, MNRK, KNRK, and MEF) and HeLa cells, but not with some other cells of human origin (ALL and WI-38). The reactivity with antibody of the plasma membrane myosin is unaffected by trypsin treatment or fixation with 0.5-2.0% formalin. These results strongly suggest that myosin in cultured nonmuscle cells is a component of the plasma membrane, a finding of possible significance in studying the mechanisms regulating the motility, morphology, and growth of these cells.

Action of Escherichia coli enterotoxin: adenylate cyclase behavior of intestinal epithelial cells in culture

Heat-labile enterotoxin preparations obtained from two enteropathogenic strains of Escherichia coli of porcine and human origin were shown to stimulate adenylate cyclase activity of human embryonic intestinal epithelial cells in culture. Comparable results were also obtained when cholera toxin was used. The degree of enzyme stimulation was proportional to the concentration of enterotoxin. Similar preparations from two strains of non-enterotoxigenic E. coli had no effect on adenylate cyclase activity. Cells exposed to enterotoxin could be washed after 1 min of contact time without altering the subsequent course of maximum adenylate cyclase activity, which was maintained for at least 18 h at 37 C. During long periods (18 h) of tissue culture incubation, the determination of adenylate cyclase activity was 200- to 300-fold more sensitive than quantitating fluid accumulation in the adult rabbit ileal loop model. Decreasing the incubation time appreciably reduced the sensitivity of the epithelial cells to enterotoxin. E. coli enterotoxin is an effective activator of nonintestinal adenylate cyclase systems. Treatment of KB and HEp-2 cell lines with enterotoxin also resulted in significant enzyme stimulation. The intestinal epithelial cell tissue culture model provides a sensitive homogenous biological system for studying the response of intestinal adenylate cyclase to enterotoxin while eliminating the numerous cellular and tissue components present in the ligated ileal loop model.

Role of cyclic 3':5'-adenosine monophosphate in the early transport changes induced by serum and insulin in quiescent fibroblasts

Serum or insulin added to quiescent mouse-embryo fibroblasts produced rapid increases in the rate of transport of uridine and phosphate and a decrease of the intracellular concentration of cyclic AMP. Incubation of the cells with prostaglandin E(1), theophylline, or both prevented the increase in uridine transport produced by serum or insulin. Prostaglandin E(1) was more effective than prostaglandins E(2) and B(1). Kinetic experiments showed that the addition of prostaglandin E(1) and theophylline causes the uridine transport rate to return to the basal level within 5 min; the rate rose rapidly after their removal. Similar effects were obtained when insulin was used instead of serum. Associated with these transport changes were significant variations in the levels of cyclic AMP. An inverse correlation between the changes in uridine transport and those in cyclic AMP concentration was shown under various experimental conditions. In contrast to the effects observed with uridine transport, phosphate uptake was only slightly affected by changes in the endogenous level of cyclic AMP. We propose that at least two different sorts of membrane changes are rapidly initiated by serum, one under cyclic AMP control and the other not related to this nucleotide.

Interrelationship between adenylate cyclase activity, adenosine 3':5' cyclic monophosphate phosphodiesterase activity, adenosine 3':5' cyclic monophosphate levels, and growth of cells in culture

To investigate how cell population density influences the intracellular concentration of cyclic AMP we have measured adenylate cyclase and cyclic AMP phosphodiesterase activities and cyclic AMP levels at various stages of cell density in normal rat-kidney (NRK) cells, which exhibit contact-inhibition of growth, and in normal chick-embryo fibroblasts (CEF), which do not show contact inhibition of growth under our conditions. Until NRK cells reach confluency, both activities increase with increasing cell population and cyclic AMP levels are low. As NRK cells reach confluency, cyclic AMP phosphodiesterase activity decreases somewhat whereas adenylate cyclase activity continues to rise. This increase in synthetic ability is accompanied by the increase in cyclic AMP levels which occurs in these cells at confluency. In CEF grown in 5% serum where density-dependent inhibition of growth is not observed, both adenylate cyclase and cyclic AMP phosphodiesterase activities increase proportionately with increasing cell population density. No significant alteration occurs in the ratio between these two enzyme activities and no change is observed in cyclic AMP levels. The NaF-stimulated activity in NRK cells increases with increasing cell density until the cells reach confluency; thereafter the NaF-stimulated activity remains constant. In contrast, the NaF-stimulated activity observed in CEF does not vary appreciably between light and heavy density. The observed changes in the enzymes of cyclic AMP metabolism accurately reflect the changes in cyclic AMP concentration as a function of cell population density. The data indicate that these two enzyme activities respond to increasing cell density to elicit a rise in intracellular cyclic AMP levels. The elevated cyclic AMP levels are thought to be involved in the regulation of cellular growth rate and the mediation of contact inhibition of growth.

A mutant of 3T3 cells with cyclic AMP metabolism sensitive to temperature change

A mutant line of 3T3 (mouse fibroblast) cells with temperature-sensitive cyclic AMP (cAMP) metabolism was isolated by selecting for low substratum adhesiveness after a change in temperature. Although the mutant is identical in behavior to the parent cell at constant temperature, a rise or fall in temperature causes a fall in intracellular cAMP levels within seconds, followed by loss of adherence to the culture dish and retraction of cell processes. The mechanism of this fall in cAMP level is at least in part excretion into the medium. The decrease in adhesiveness and retraction of processes can be blocked by analogues of cAMP or agents that elevate intracellular cAMP. The properties of this mutant imply that cAMP is a direct regulator of cell shape and adhesiveness.