Subfractionation of rat liver plasma membrane: Uneven distribution of plasma membrane-bound enzymes on the liver cell surface

Plasma membranes were islotaed from rat liver mainly under isotonic conditions. As marker enzymes for the plasma membrane, 5′-nucleotidase and (Na⁺+K⁺)-ATPase were used. The yield of plasma membrane was 0.6–0.9 mg protein per g wet weight of liver. The recovery of 5′-nucleotidase and (Na⁺+K⁺)-ATPase activity was 18 and 48% of the total activity of the whole-liver homogenate, respectively. Judged from the acitvity of glucose-6 phosphatase and succinate dehydrogenase in the plasma membrane, and from the electron microscopic observation of it, the contamination by microsomes and mitochondria was very low. A further homogenization of the plasma membrane yielded two fractions, the light and heavy fractions, in a discontinuous sucrose gradient centrifugation. The light fraction showed higher specific activities of 5′-nucleotidase, alkaline phosphatase, (Na⁺+K⁺)-ATPase and Mg²⁺-ATPase, whereas the heavy one showed a higher specific activity of adenylate cyclase. Ligation of the bile duct for 48 h decreased the specific activities of (Na⁺+K⁺)-ATPase and Mg²⁺-ATPase in the light fraction, whereas it had no significant influence on the activities of these enzymes in the heavy fraction. The specific activity of alkaline phosphatase was elevated in both fractions by the obstruction of the bile flow. Electron microscopy on sections of the plasma membrane subfractions showed that the light fraction consisted of vesicles of various sizes and that the heavy fractions contained membrane sheets and paired membrane strips connected by junctional complexes, as well as vesicles. The origin of these two fractions is discussed and it is suggested that the light fraction was derived from the bile front of the liver cell surface and the heavy one contained the blood front and the lateral surface of it.     

Characterization of adenylate and guanylate cyclases in rat peritoneal mast cells

Adenylate and guanylate cyclase activities were confirmed in crude homogenates from rat peritoneal mast cells. Both enzyme activities were associated with the 105, 000 X g particulate fractions, but not detected in the supernatant fractions. The optimal pH for both cyclase activities was 8.2. Mn⁺⁺ was essentially required for guanylate cylcase activity, while adenylate cyclase activity was observed in the presence of either Mg⁺⁺ or Mn⁺⁺. The apparent Km values of adenylate cyclase for Mn⁺⁺-ATP and Mg⁺⁺-ATP were 160 μM and 340 μM, respectively, whereas the value of guanylate cyclase for Mn⁺⁺-GTP was 100 μM. Adenylate cyclase was activated by 10 mM NaF. However, both adenylate and guanylate cyclase activities were neither stimulated nor inhibited by the addition of various kinds of agents which stimulate or inhibit the release of histamine from mast cells.     

Modification of the erythrocyte membrane by sulfhydryl group reagents

Summary In this study, the consequences of modification of human erythrocyte membrane sulfhydryl groups by N-ethyl maleimide (NEM), 5,5dithiobis-(2-nitrobenzoic acid) (DTNB) andp-hydroxymercuriphenyl sulfonate (PHMPS) were investigated. These reagents differ in chemical reactivity, membrane penetrability and charge characteristics.Results of sulfhydryl modification were analyzed in terms of inhibitory effects on activities of five membrane enzymes; Mg⁺⁺- and Na⁺, K⁺-ATPase, K⁺-dependent and independentp-nitrophenyl phosphatase (NPPase) and DPNase. Structural considerations involved in the sulfhydryl-mediated inhibition were evaluated by studying the changes in susceptibility to sulfhydryl alteration produced by shearing membranes into microvesicles and by the addition of the membrane modifiers, Mg⁺⁺ and ATP.Conclusions from the data suggest that the effects of NEM appeared to result from modification of a single class of sulfhydryls; DTNB interacted with two different sulfhydryl classes. Increasing concentrations of PHMPS resulted in the sequential modification of many types of sulfhydryls, presumably as a result of increasing membrane structural disruption. DTNB and PHMPS caused solubilization of about 15% of membrane protein at concentrations giving maximal enzyme inhibition.In contrast to the usually observed parallels between Na⁺, K⁺-ATPase and K⁺-dependent NPPase, activities of Mg⁺⁺-ATPase, Na⁺, K⁺-ATPase and K⁺-dependent NPPase varied independently as a result of sulfhydryl modification. We suggest complex structural and functional relationships exist among these components of the membrane ATP-hydrolyzing system.Our studies indicate that the effects of sulfhydryl group reagents on these membrane systems should not be ascribed to sulfhydryl modificationper se, but rather to the resulting structural perturbations. These effects depend upon the structural characteristics of the particular membrane preparation studied and on the chemical characteristics of the sulfhydryl group reagent used.     

Studies on isolated subcellular components of cat pancreas

Summary Pancreas of the cat was fractionated into its subcellular components by centrifugation through an exponential ficoll-sucrose density gradient in a zonal rotor. This enables a preparation of four fractions enriched in plasma membranes, endoplasmic reticulum, mitochondria and zymogen granules, respectively. The first fraction, enriched by 9- to 15-fold in the plasma membrane marker enzymes, hormone-stimulated adenylate cyclase, (Na⁺K⁺)-ATPase, and 5-nucleotidase, is contaminated by membranes derived from endoplasmic reticulum but is virtually free from mitochondrial and zymogen-granule contamination. The second fraction from the zonal gradient shows only moderate enrichment of the above marker enzymes but contains a considerable quantity of plasma membrane marker enzymes and represents mostly rough endoplasmic reticulum. The third fraction contains the bulk of mitochondria and the fourth mainly zymogen granules as assessed by electron microscopy and marker enzymes for both mitochondria and zymogen granules, namely succinic dehydrogenase, trypsin and amylase. Further purification of the plasma membrane fractions by differential and sucrose step-gradient centrifugation yields plasma membrane enriched 40-fold in basal and hormone-stimulated adenylate cyclase and (Na⁺K⁺)-ATPase.     

Isolation and Partial Characterization of an Acetylcholine Receptor-Enriched Membrane Fraction from Skeletal Muscle

Abstract

A procedure for purification of the bungarotoxin-binding fraction of sarcolemma from rabbit skeletal muscle is described. Muscle is homogenized in 0.25M sucrose without high salt extraction and membrane fractions separated initially by differential centrifugation procedures. An ultracentrifugation pellet enriched in cell surface and sarcoplasmic reticulum markers is further fractionated on a dextran gradient (density = 1.0 to 1.09). Two fractions are identified as sarcolemma according to high specific activities for lactoperoxidaseiodination, Na⁺, K⁺-ATPase and α-bungarotoxin-binding. No Ca⁺⁺, Mg⁺⁺-ATPase activity is found in these fractions. A third fraction, the dextran gradient pellet, is enriched in Ca⁺⁺, Mg⁺⁺-ATPase activity and lactoperoxidase iodinatable material and characterized by low bungarotoxin binding. This fraction represents a mixture of sarcoplasmic reticulum and transverse tubules with some sarcolemma contamination.     

Adenylate cyclase activity of membrane fractions isolated from sea urchin sperm

The adenylate cyclase activity of sperm membrane fragments isolated from Lytechinus pictus sperm according to Cross [20] has been studied. Two distinct fractions preferentially coming from the flagellar plasma membrane are obtained. Surface I¹²⁵-labeling experiments performed by Cross [20] indicate that these membranes are representative of the entire sperm plasma membrane. Both fractions are enriched in their adenylate cyclase activity: the specific activity of the top membranes is eightfold higher than in whole sperm, whereas that of the middle membranes is 15-fold higher. The cyclase seems to be associated with the membranes. Lytechinus pictus egg jelly has no effect or slightly inhibits the adenylate cyclase activity of the isolated sperm plasma membrane fragments. Mg⁺⁺ and Na⁺ stimulated their cyclase activity about sevenfold at 2.5 mM Mn⁺⁺ and 3.2 mM ATP. At this ATP to Mn⁺⁺ ratio, high concentrations of Ca⁺⁺ have a small stimulatory effect.     

Effect of concanavalin A on membrane-bound enzymes from mouse lymphocytes

The ionic influence and ouabain sensitivity of lymphocyte Mg²⁺-ATPase and Mg²⁺-(Na⁺ + K⁺)-activated ATPase were studied in intact cells, microsomal fraction and isolated plasma membranes. The active site of 5′-nucleotidase and Mg²⁺-ATPase seemed to be localized on the external side of the plasma membrane whereas the ATP binding site of (Na⁺ + K⁺)-ATPase was located inside the membrane.Concanavalin A induced an early stimulation of Mg²⁺-ATPase and (Na⁺ + K⁺)-ATPase both on intact cells and purified plasma membranes. In contrast, 5′-nucleotidase activity was not affected by the mitogen. Although the thymocyte Mg²⁺-ATPase activity was 3–5 times lower than in spleen lymphocytes, it was much more stimulated in the former cells (about 40 versus 20 %). (Na⁺ + K⁺)-ATPase activity was undetectable in thymocytes. However, in spleen lymphocytes (Na⁺ + K⁺)-ATPase activity can be detected and was 30 % increased by concanavalin A. Several aspects of this enzymic stimulation had also characteristic features of blast transformation induced by concanavalin A, suggesting a possible role of these enzymes, especially Mg²⁺-ATPase, in lymphocyte stimulation.     

Preparation of renal cortex basal-lateral and brush border membranes. Localization of adenylate cyclase and guanylate cyclase activities

Luminal brush border and contraluminal basal-lateral segments of the plasma membrane from the same kidney cortex were prepared. The brush border membrane preparation was enriched in trehalase and γ-glutamyltranspeptidase, whereas the basal-lateral membrane preparation was enriched in (Na⁺ + K⁺)-ATPase. However, the specific activity of (Na⁺ + K⁺)-ATPase in brush border membranes also increased relative to that in the crude plasma membrane fraction, suggesting that (Na⁺ + K⁺)-ATPase may be an intrinsic constituent of the renal brush border membrane in addition to being prevalent in the basal-lateral membrane. Adenylate cyclase had the same distribution pattern as (Na⁺ + K⁺)-ATPase, i.e. higher specific activity in basal-lateral membranes and present in brush border membranes. Adenylate cyclase in both membrane preparations was stimulated by parathyroid hormone, calcitonin, epinephrine, prostaglandins and 5′-guanylylimidodiphosphate. When the agonists were used in combination enhancements were additive. In contrast to the distribution of adenylate cyclase, guanylate cyclase was found in the cytosol and in basal-lateral membranes with a maximal specific activity (NaN₃ plus Triton X-100) 10-fold that in brush border membranes. ATP enhanced guanylate cyclase activity only in basal-lateral membranes. It is proposed that guanylate cyclase, in addition to (Na⁺ + K⁺)-ATPase, be used as an enzyme “marker” for the renal basal-lateral membrane.     

Isolation and characterization of plasma membrane from lactating bovine mammary gland

Plasma membranes were isolated from lactating bovine mammary gland. Two crude membrane fractions; medium/d 1.033 (light membrane) and 1.033/1.053 interfaces (heavy membrane), were obtained by Ficoll density gradient centrifugation of osmotically washed microsomal fraction. Two crude membranes were further purified separately by sucrose density gradient centrifugation. Both light and heavy membranes banded at a sucrose density of 1.14. The purified membranes appeared as heterogeneous smooth membrane vesicles on electron microscopy. The contaminating suborganelles were not detected. The yield of the purified membranes relative to the homogenate was 1.2%. The degree of purity of the membranes was shown by a great increase in the specific activity of 5′-nucleotidase over the homogenate of 20-fold for light membrane and of 16-fold for heavy membrane. The relative activities of Mg²⁺-ATPase, (Na⁺ + K⁺)-ATPase, γ-glutamyl transpeptidase, phosphodiesterase I, akaline phosphatase and xanthine oxidase were also high (12–18-times) and nearly 20% of these enzymes was recovered. The activity of marker enzyme for mitochondria, endoplasmic reticulum and Golgi apparatus was very low, while that of acid phosphatase for lysosome was relatively high (5-times). DNA and RNA contents were very low. The major polypeptides rich in other suborganelles were not detected profoundly in the membrane fraction and the polypeptide compositions in both light and heavy membranes were similar upon SDS-polyacrylamide gel electrophoresis.     

Modulation of single cardiac Na+ channels by cytosolic Mg++ ions

Elementary Na⁺ currents were recorded in inside-out patches excised from cultured neonatal rat heart myocytes in order to study the influence of cytosolic Mg⁺⁺ and other bivalent cations present at the cytoplasmic membrane surface on cardiac Na⁺ channel gating. Exposing the cytoplasmic membrane surface to a Mg⁺⁺-free environment shortened the open state of cardiac Na⁺ channels significantly. _open declined to 62±2% of the value obtained at 5 mmol/l Mg_i ⁺⁺. Other channel properties including the tendency to reopen and the elementary current size either changed insignificantly within a 10% range or remained completely unchanged. An almost identical change of _open can be caused by switching from a Mn⁺⁺ (5 mmol/l) containing internal solution to a Mn⁺⁺-free internal solution. But _open failed to significantly respond to a variation in internal Ni⁺⁺ from 5 mmol/l to 0 mmol/l. The same response to internal Mg⁺⁺ withdrawal was obtained with (–)-DPI-modified, non-inactivating Na⁺ channels, indicating that the exit rate from the open state remains as sensitive to cytosolic Mg⁺⁺ variations as in normal Na⁺ channels with operating inactivation. Offprint requests to: M. Kohlhardt     

Adenylate cyclase system of human skeletal muscle: Characteristics of catecholamine stimulation and nucleotide regulation

The subcellular localization of adenylate cyclase was examined in human skeletal muscle. Three major subcellular membrane fractions, plasmalemma, sarcoplasmic reticulum and mitochondria, were characterized by membrane-marker biochemical studies, by dodecyl sulfate polycrylamide gel electrophoresis and by electron microscopy. About 60% of the adenylate cyclase of the homogenate was found in the plasmalemmal fraction and 10–14% in the sarcoplasmic reticulum and mitochondria. When the plasmalemmal preparation was subjected to discontinuous sucrose gradients, the distribution of adenylate cyclase in different subfractions closely paralleled that of (Na⁺ + K⁺)-ATPase. The highest specific activity was found in a fraction which setteled at the 0.6–0.8 M sucrose interface. The electron microscopic study of this fraction revealed the presence of flattened sacs of variable sizes and was devoid of mitochondrial and myofibrillar material. The electron microscopy of each fraction supported the biochemical studies with enzyme markers. The three major membrane fractions also contained a low K_m phosphodiesterase activity, the highest specific activity being associated with sarcoplasmic reticulum.The plasmalemmal adenylate cyclase was more sensitive to catecholamine stimulation than that associated with sarcoplasmic reticulum or mitochondria. The catecholamine-sensitive, but not the basal, enzyme was further stimulated by GTP. The plasmalemmal adenylate cyclase had typical Michaelis-Menten kinetics with respect to ATP and the apparent K_m for ATP was approx. 0.3. mM. The pH optimum for that enzyme was 7.5. The enzyme required Mg²⁺, and the concentration to achieve half-maximal stimulation was approx. 3 mM. Higher concentrations of Mg²⁺ (about 10 mM) were inhibitory. Solubilization of the plasmalemmal membrane fraction with Lubrol-PX resulted in preferential extraction of 106 000- and 40 000-dalton protein components. The solubilized adenylate cyclase lost its sensitivity for catecholamine stimulation, and the extent of fluoride stimulation was reduced to one-sixth of that of the intact membranes. It is concluded that the catalytically active and hormone-sensitive adenylate cyclase is predominantly localized in the surface membranes of the cells within skeletal muscle. (That “plasmalemmal” fraction is considered likely to contain, in addition to plasmalemma of muscle cells, plasmalemma of bloodvessel cells (endothelium, and perhaps smooth muscle) which may be responsible for a certain amount of the adenylate cyclase activity and other propertiesobserved in that fraction.)The method of preparation used in this study provides a convenient material for evaluating the catecholamine-adenylate cyclase interactions in human skeletal muscle.     

Characterization of plasma membrane domains of mouse EL4 lymphoma cells obtained by affinity chromatography on concanavalin A-Sepharose

Purified plasma membranes of mouse EL₄ lymphoma cells were fractionated by means of affinity chromatography on concanavalin A-Sepharose into two subfractions; one (MF1) eluted freely from the affinity column, the second (MF2) adhered specifically to Con A-Sepharose. Both membrane subfractions proved to be of plasma membrane origin, as evidenced by the following criteria. (i) The ratio of cholesterol to phospholipid was nearly identical in plasma membrane and both subfractions. (ii) When isolated plasma membranes were labelled with tritiated NaBH₄, both subfractions exhibited identical specific radioactivities. (iii) After enzymatic radioiodination of the cells, the total content of labelled proteins was very similar in isolated plasma membranes and in both subfractions. (iv) Some plasma membrane marker enzymes exhibited nearly identical specific activities in plasma membranes, MF1 or MF2 including γ-glutamyl transpeptidase, 5′-nucleotidase and Mg²⁺-ATPase. Both subfractions exhibited characteristic differences. Thus the specific activities of (Na⁺ + K⁺)-ATPase, Ca²⁺-ATPase and lysophosphatidylcholine acyltransferase were several-fold enriched in MF2 compared to MF1. SDS-polyacrylamide gel electrophoresis revealed a different polypeptide composition of the two subfractions. Polypeptides of apparent molecular mass of 116, 95, 42, 39, 30 and 28 kDa were highly enriched in MF2, whereas MF1 contained another set of proteins, of apparent molecular mass of 70, 55 and 24 kDa. The phospholipid fatty acid composition of the subfractions proved to be different, as well, MF2 contained more saturated fatty acids than MF1. The data suggest the existence of plasma membrane domains in the plasma membranes of the mouse EL₄ lymphoma cells, containing a set of polypeptides, among others membrane bound enzymes, embedded in a different phospholipid milieu.     

Distribution of selected phospholipid modifying enzymes in rat brain microsomal subfractions prepared by density gradient zonal rotor centrifugation

A rat brain P₃ fraction enriched in ER derived microsomes was centrifuged through a 20–40% linear sucrose gradient in a Beckman Ti-14 Zonal rotor and 11 fractions were obtained. The distribution of marker enzyme activities and protein were determined in these 11 subfractions. NADPH-Cytochrome C reductase, choline phosphotransferase were employed for endoplasmic reticulum, Na⁺, K⁺-ATPase, 5-nucleotidase, and acetylcholinesterase were employed for plasma membrane, 2, 3-cyclic nucleotide phosphohydrolase was employed for myelin. The bulk of the protein was recovered in the 24–34% sucrose fractions, Na⁺, K⁺-ATPase, 5-nucleotidase, and acetylcholinesterase were in the 22–38% sucrose fractions while NADPH-cytochrome C reductase and CNPase were enriched in the 20–22% sucrose fractions. The ethanolamine and the serine base exchange activities had a bimodal distribution, with highest specific activities in sucrose fractions 32–34% and 20–24%. Choline base exchange activity was nearly undetectable in all the fractions. The specific activities of CDP-choline phosphotransferase, and phospholipid-N-methyltransferase were highest in the 20–22% sucrose fraction. Phospholipid-N-methyltransferase activity was significantly stimulated in the presence of exogenous phospholipid acceptors as phosphatidylethanolamine or phosphatidylmonomethylethanolamine or phosphatidyldimethylethanolamine, however, the greatest response was with phosphatidylmonomethylethanolamine. The rat brain P₃ fraction yielded a population of a membrane at the light end of the sucrose gradient which has a buoyant density similar to myelin but seemed to be enriched with NADPN cytochrome C reductase and phospholipid modifying enzymes. This is in contrast to liver microsomes submitted to a similar fractionation.     

Synaptosomal non-mitochondrial ATPase activities and drug treatment

Energy-using non-mitochondrial ATPases were assayed in rat cerebral cortex synaptosomes and synaptosomal subfractions, namely synaptosomal plasma membranes and synaptic vesicles. The following enzyme activities were evaluated: Na⁺, K⁺-ATPase; high- and low-affinity Ca²⁺-ATPase; basal Mg²⁺-ATPase; Ca²⁺, Mg²⁺-ATPase. The evaluations were performed after four week-treatment with saline [controls] or -adrenergic agents (-yohimbine, clonidine), energymetabolism interfering compound (theniloxazine), and oxygen-partial pressure increasing agent (almitrine), in order to define the plasticity and the selective changes in individual ATPases. In rat cerebral cortex, the enzyme adaptation to four-week-treatment with -yohimbine or clonidine was characterized by increase in both high- and low-affinity Ca²⁺-ATPase activities. The action involves the enzyme form located in the synaptic plasma membranes. The enzyme adaptation to the subchronic treatments with theniloxazine or almitrine was characterized by increase in Na⁺, K⁺-ATPase or Mg²⁺-ATPase activities, respectively. The action involves the enzymatic forms located in the synaptic plasma membranes. Thus, the pharmacodynamic effects of the agents tested should also be related to the changes induced in the activity of some specific synaptosomal nonmitochondrial ATPases.     

Modifications of adenylate and guanylate cyclase activities during multiplication of KB cells.

Adenylate and guanylate cyclase activities do not vary in concert during the multiplication of KB cells. Adenylate cyclase activity is low and slightly increases at cell confluency, guanylate cyclase activity, great in sparce cells, decreases during cell multiplication period. These variations are not caused by a modification of catalytic sites because the apparent Km for ATP or GTP is not changed, but by a modification of the dependance on Mg⁺⁺ or Mn⁺⁺ ions. Fresh serum increases guanylate cyclase activity but does not affect adenylate cyclase.     

Ultrastructural cytochemistry of membrane-bound phosphatases in preimplantation mouse embryos.

The time of appearance and the ultrastructural localization of the enzyme activity of alkaline phosphatase (AlkPase), 5′-nucleotidase (5′Nuc), Mg²⁺-ATPase, transport ATPase, cyclic AMP phosphodiesterase (cAMP-PDase), and adenylate cyclase (AC) were investigated in unfertilized eggs and in mouse preimplantation embryos. Enzyme activity was associated only with the plasma membrane. AlkPase activity appeared only in limited areas of the plasma membrane of one-cell embryos and increased in the eight-cell and morula stages. In blastocysts, the enzyme activity was concentrated mainly in the trophoblast cells. 5′Nuc activity appeared first in four- or eight-cell embryos and the highest activity was observed in trophoblast cells in the blastocyst and in plasma membrane between cells forming inner cell mass. Mg²⁺-activated ATPase activity was present in all embryos and in unfertilized egg plasma membrane. Transport (Na⁺K⁺)-ATPase appeared only in the closely apposed membranes of adjacent cells in morulae and blastocysts. A very low cAMP-PDase activity appeared between adjacent cells in two-cell embryos, and the highest activity was observed on the outer surface of the plasma membrane of trophoblasts. AC was the only enzyme whose activity was located on the inner (cytoplasmic) side of the plasma membrane and appeared as early as the one-cell stage embryo. The relation between the time of the appearance of enzyme activity and the preparation of embryos for implantation and upon embryonic proliferative activity is discussed.     

A comparison of the subcellular distribution of 5′-nucleotidase, (Na+K+)-ATPase and adenyl cyclase in beef thyroid gland

The validity of 5′-nucleotidase as a plasma membrane marker enzyme in beef thyroid has been tested by comparing the subcellular distribution of its activity to that of (Na⁺K⁺)-activated ATPase and adenyl cyclase. The specific activity and total activity of (Na⁺K⁺)-ATPase and adenyl cyclase were greatest in the 1000 × g (“nuclear”) and 33 000 × g (“mitochondrial and lysosomal”) fractions. In contrast, 5′-nucleotidase activity was concentrated in the 165 000 × g (“microsomal”) pellet and supernatant. Partially purified plasma membranes were separated from the 1000 (N₂), 30 000 (M₂) and 165 000 × g (P₂) pellets by discontinuous sucrose gradient centrifugation. Again a discordant distribution of these enzyme activities was observed. (Na⁺K⁺)-ATPase specific activity was increased approximately 30-fold over the homogenate in Fractions N₂ and M₂. Basal, thyroid-stimulating hormone-and fluoride-stimulated adenyl cyclase activities were concentrated in the same fractions. 5′-Nucleotidase activity was preferentially located in M₂ and P₂. These differences in distribution pattern suggest that 5′-nucleotidase activity is not uniquely located in the plasma membrane in the thyroid.     

Study of some enzyme activities in cultured chick embryo brain nerve cells treated by chick embryo brain extracts

Brain extracts from 8-day-old chick embryos have been shown to influence morphological development of dissociated brain cells from 7-day-old chick embryos in culture. Stimulatory, effects on size of the neuronal somas and on growth of long processes were observed by adding the cytosol of the brain extract or the dialysate of the cytosol. These morphological changes parallel modifications of various enzyme activities according to the age of the cultures. Adenyl cyclase, (Na⁺, K⁺)- and Mg²⁺-ATPase, 5-nucleotidase, choline acetyltransferase, and acetylcholinesterase activities were studied between 5 and 14 days of culture. Adenyl cyclase activity was strongly stimulated at 8 days by both extracts. (Na⁺, K⁺)-and Mg²⁺-ATPase activities were stimulated in 8-day-old cultures only by the dialysate. 5-Nucleotidase activity was stimulated in 8-day-old cultures by the dialysate and in 11-day-old cultures by both extracts. Choline acetyltransferase activity was stimulated by the cytosol in 8-day-old cultures and by the dialysate in 11-day-old cultures. The total acetylcholinesterase activity was higher in 8-, 11-, and 14-day-old cultures treated with the cytosol. When the cells were treated with the dialysate, the activity was only higher in 14-day-old cultures. We also found that following the addition of brain extracts, the specific activity of the enzymes we studied was enhanced and became close to the values found in vivo during embryogenesis. Thus in parallel to the morphological modifications observed in nerve cell cultures treated by embryo brain extracts, biochemical variations especially involved in synaptogenesis and membrane development could be measured.     

Adenylate cyclase activity in porcine sperm in response to female reproductive tract secretions

Adenylate cyclase activities were studied in porcine sperm in the presence and absence of Mn⁺⁺ before and after incubation in vivo and in vitro. Incubation of sperm in vivo for 30 min increased the Mg⁺⁺-stimulated adenylate cyclase activity from 35.1 pmoles cyclic AMP formed per mg protein per 10 min to 50.4 pmoles. The activity stimulated by Mg⁺⁺ and Mn⁺⁺ increased from 392 to 729 pmoles after 30 min of in vivo incubation. Activity after incubation in vivo for 120 min was not different from activity after 30 min. In vitro incubation of porcine sperm in Ca⁺⁺-free Ringer-fructose resulted in no change, but incubation in oviductal and uterine flushings obtained from gilts soon after ovulation increased Mg⁺⁺-stimulated activity by 24% and Mg⁺⁺?+ Mn⁺⁺-stimulated activity by 49%. In vitro incubations in preovulatory flushings plus follicular fluid or in bovine serum albumin also increased adenylate cyclase activity.