Suppression of adrenocorticotropic hormone (ACTH)-induced corticosterone secretion in cultured rat adrenocortical cells by gossypol and gossypolone

We have reported that gossypol, an antifertility agent, and gossypolone, a major metabolite of gossypol, inhibited steroidogenesis in bovine luteal cells in vitro. In the current study, the effects of these two compounds on steroidogenesis were examined in adrenocortical cells of young rats. ACTH-induced corticosterone secretion and intracellular adenosine monophosphate (cAMP) formation were significantly inhibited by gossypol at concentrations of 8.6 and 4.3 microM, respectively, and by gossypolone at concentrations of 8.6 and 4.3 microns, respectively. The present study demonstrated that both compounds inhibit ACTH-induced corticosterone synthesis and secretion in rat adrenocortical cell and this inhibition is, at least partially, attributed to the reduction of intracellular cAMP formation. Our data suggest that gossypol and its metabolite(s) probably affect steroidogenesis not only in gonads but also in adrenal glands by a common mean-reduction of intracellular cAMP.

Gossypol effects on monoamine oxidase (MAO) activity in several organs of term rats

In order to study the effect of gossypol on the monoamine oxidase (MAO) activity in pregnant rat organs, 20 day pregnant rats were sacrificed, and MAO activity/0.02 g tissue of several organs and total MAO activity/organ, were determined. The control group (n = 5) were injected with vehicle intramuscularly on the 17th, 18th and 19th day of pregnancy, and the gossypol treated group (n = 4) were injected with gossypol acetic acid (GAA) (25 mg/kg of body weight) intramuscularly on the 17th, 18th and 19th day and were decapitated on the 20th day of pregnancy. Maternal liver, uterus, placenta, and fetal liver were collected and examined. In placenta, total MAO activity/organ was significantly (p less than 0.05) lower in the GAA treated group than that in the control group. However, in maternal liver, uterus and fetal liver, there was no significant difference in total MAO activity/organ between the two groups. There was no significant difference in MAO activity/0.02 g tissue (specific activity), weight of organ, protein weight/organ and protein/g tissue between the two groups in maternal liver, uterus, placenta and fetal liver. These results suggest that, after intramuscular injection of GAA, total MAO activity/organ in the placenta of pregnant rats might decrease significantly.

Gossypol pharmacokinetics in mid-lactation Brown Swiss dairy cows

A bolus equivalent to 450 ppm (dosage based on average feed intake for lactating dairy cows of similar mass) of gossypol was administered orally to three Brown Swiss dairy cows in mid lactation daily for a 7-day treatment period. Blood samples were taken during a 2-day pretreatment period, the 7-day treatment period and a 6-day recovery period. The serum recovered from the cows was stored at -20 degrees C until analysis for extractable gossypol content. The highest concentration of gossypol (a mean of 0.53 microgram/ml serum) was attained in all the cows on day 6 of the treatment period, indicating that a steady-state condition had been reached before the end of the treatment period. The gossypol concentrations then gradually declined during the 6-day recovery period but never fell to the zero baseline. The cows exhibited terminal elimination half-lives of 67, 67.5 and 40 h. Gossypol elimination was best described by a bi-exponential decay curve in two cows and a mono-exponential decay curve in the remaining cow.

[Vascular anastomosis using CO2 laser: an experimental study]

This experiment was done on 50 left side carotid communal arteries of rats. The arteries were cut and then anastomosed by welding using CO2 laser which produced by a self design laser microsurgical machine which was designed by us, while the right side arteries as control were anastomosed by conventional suturing with 11/0 nylon thread. The results showed that the patency rate was 100% in both groups either immediately or 1 hour, 3 days, and 10 days and 2 months after operation. The operative time of the laser group is about 5-6 min shorter than the sutured group which took 10-15 min. The anastomotic quality was examined by scanning electronmicroscopy. The results showed: On the third day the endothelium growth rate was 18% and on the 10th day was 98% in the laser group which was very close to the sutured group.

Effect of obstructive jaundice on renal Na-K ATPase activity and ATP contents, their response to E. coli or endotoxin and effect of 1-6 fructose diphosphate

A two-week bile duct ligation (BDL) in Sprague-Dawley (SD) rats raised the serum billirubin level and decreased the mean arterial blood pressure and renal cortical ATP contents compared with those in sham-operated (SO) rats (3.6 +/- 1.15 mg% vs 0.54 +/- 0.36, P less than 0.001; 69 +/- 24 mmHg vs 86 +/- 21, P less than 0.05; 3.72 +/- 0.86 x 10(-10) mol/mg tissue vs 7.27 +/- 0.18, P less than 0.05). No difference could be found in the medullary ATP contents (8.42 +/- 2.20 vs 8.70 +/- 2.80, P = NS). In SO rats, injection of endotoxin (0.7 mg/kg BW) and E. coli (3.1 x 10(5) bacteria/100 g BW) reduced cortical ATP content to 1.86 +/- 0.97 and 1.30 +/- 0.47 (P less than 0.001), and medullar ATP to 1.33 +/- 0.31 and 2.12 +/- 0.46 (P less than 0.001) respectively. In BDL rats, the same treatment led to further decrease in cortical ATP to 1.25 +/- 0.40 and 0.62 +/- 0.20, medullary ATP to 0.97 +/- 0.41 and 1.64 +/- 0.83 (P less than 0.001). Basal Na-K ATPase activity in BDL is the same compared with that in SO both in the cortex (2.85 +/- 2.2 mumol/mgpr/h vs 2.19 +/- 0.75; P = NS) and medulla (2.79 +/- 1.83 vs 3.05 +/- 1.38; P = NS).(ABSTRACT TRUNCATED AT 250 WORDS)

Properties of embryonic and adult muscle acetylcholine receptors transiently expressed in COS cells

We used transient transfection in COS cells to compare the properties of mouse muscle acetylcholine receptors (AChRs) containing alpha, beta, delta, and either gamma or epsilon subunits. gamma- and epsilon-AChRs had identical association rates for binding 125I-alpha-bungarotoxin, and identical curves for inhibition of toxin binding by d-tubocurarine, but epsilon-AChRs had a significantly longer half-time of turnover in the membrane than gamma-AChRs. A myasthenic serum specific for the embryonic form of the AChR reduced toxin binding to gamma-, but not epsilon-AChRs. The gamma-AChRs had channel characteristics of embryonic AChRs, whereas the major class of epsilon-AChR channels had the characteristics of adult AChRs. Two minor channel classes with smaller conductances were also seen with epsilon-AChR. Thus, some, but not all, of the differences between AChRs at adult endplates and those in the extrasynaptic membrane can be explained by the difference in subunit composition of gamma- and epsilon-AChRs.

Taenia taeniaeformis: inactivation of metacestodes by gossypol in vitro

Gossypol, a natural biphenyl compound inhibits Taenia taeniaeformis metacestode development in vivo. In this paper, the direct effect of gossypol on metacestodes was examined. Within 24 hr of incubation at 37 degrees C in greater than or equal to 10(-5) M gossypol, shedding of the tegument from the surface of the metacestodes was observed. There was a significant decrease in [3H]thymidine uptake by T. taeniaeformis in greater than or equal to 10(-5)M gossypol. In addition, NADH lactate dehydrogenase activity of metacestodes was significantly inhibited in greater than or equal to 10(-5) M gossypol. Thus, gossypol has a direct inhibitory effect on T. taeniaeformis metacestodes in vitro.

[Preparation conditions for decoction of Epimedium grandiflorum Morr]

The time, volume and method in preparing decoction of Epimedium grandiflorum have been studied by orthogonal design through the determination of icariin. The factors which influence decoction-making conditions are in the order of: volume greater than time greater than method.

Inhibitory effect of gossypol on steroidogenic pathways in cultured bovine luteal cells

Gossypol inhibits the reproductive system and steroidogenesis in both sexes. The present study investigated some possible sites subsequent to cAMP formation at which gossypol may inhibit progesterone biosynthesis. Bovine luteal cells were cultured with dibutyryl cAMP (dbcAMP), 25-OH cholesterol, or pregnenolone in the presence or absence of gossypol. Gossypol, at 17-34 microM, inhibited dbcAMP-induced progesterone secretion. Gossypol significantly inhibited the conversions of exogenous 25-OH cholesterol and pregnenolone to progesterone. However, the conversion of 25-OH cholesterol to pregnenolone was not significantly inhibited by gossypol at low doses (less than or equal to 34 microM). These results suggest that gossypol inhibits progesterone synthesis in bovine luteal cells by suppressing steroidogenic enzyme activity.

[Studies on antigens of human lung adenocarcinoma with McAb LC-1]

The soluble antigens extracted from both human lung adenocarcinoma cell line SPC-A-1, and normal adult lung tissue with non-idet P-40 were subjected to 10% SDS-PAGE. The number of bands distinguishable by naked eyes of lung adenocarcinoma are 57, in which 4 bands are more significant. The bands of normal human lung tissue are 52, in which 2 bands are more significant. The molecular weights of these bands mainly are within 30 to 94 KD The thin layer chromatographs of these two antigenic extracts have shown that there is difference in their sugar content, but both of them shown little sialic acid. The Immunoblot pattern of McAb LC-1 reacted with the extracts of SPC-A-1 cells shows that all of 3 bands detected can be stained by alcian blue, indicating that they are glycoproteins. However, of them two bands, M. W. of 70 KD and 51 KD can also be stained by Sudan Black B, indicating that these two bands are glycolipoproteins. The ganglioside and neutral glycolipid can inhibit the binding of LC-1 with the extract of SPC-A-1 cells. The results indicate that the epitopes of SPC-A-1 cell extract reacted with McAb LC-1 are probably located in the polysaccharide.

Effects of ractopamine on adipose tissue metabolism and insulin binding in finishing hogs. Interaction with genotype and slaughter weight

Twenty-four barrows were divided among eight treatments in a 2 x 2 x 2 design to quantify the influence of ractopamine (0 or 20 mg/kg diet) over the final 40 kg of gain on metabolic activity in adipose tissue. Interactions with genotype (Hampshire cross or Landrace cross) and slaughter weight (100 or 127 kg) were investigated also. Backfat was removed at slaughter and rates of lipolysis and fatty acid synthesis (FS), activities of malic enzyme (ME) and fatty acid synthetase (FAS), and insulin binding to adipocytes were assessed. Adipocytes from ractopamine-fed pigs were less sensitive (EC50 increased 90%) and had a lower maximum lipolytic response (40%) to ractopamine stimulation. Rates of basal and insulin-stimulated FS were decreased 40% in ractopamine-fed pigs and were reflected in lower activities of ME (50%) and FAS (15%). Breed and slaughter weight had no consistent influence on the ractopamine response. Landrace-cross pigs had greater insulin binding capacity (30-60%) whether data were expressed on a cell or surface area basis. Ractopamine feeding did not consistently affect insulin binding capacity. Results suggest that ractopamine interacts in vivo with the beta-adrenergic receptor of swine adipocytes, decreasing lipogenic capacity and diminishing responsiveness to beta-adrenergic stimulation.

Effects of larval tapeworm (Taenia taeniaeformis) infection on reproductive functions in male and female host rats

This report examined the effects of larval tapeworm infection on the reproductive functions in both male and female host rats. Female rats were matched by age, then randomly assigned to control and treatment groups (infected with larval tapeworms). Estrous cycles were determined by vaginal smear with 95% of the control group exhibiting 4-day normal cyclicity and only 55% of the treated group exhibiting normal cycles. Female fertility was then evaluated for the normally cycling rats based on the percentage of successful matings on the evening of proestrus, number of implantation sites on Day 8 of pregnancy, and number of pups born at term. The normally cycling rats exhibited 96% successful mating, 12.95 +/- 1.80 implantation sites, and 11.20 +/- 1.80 pups born. Five months after larval tapeworm infection, the fertility parameters were decreased to 79%, 9.10 +/- 1.20, and 7.50 +/- 1.50, respectively. The control females were then used in a study of male fertility after larval tapeworm infection employing the same parameters used to test female fertility. At the onset of the study, control groups exhibited 95% successful mating, 12.50 +/- 1.50 implantation sites, and 11.60 +/- 1.60 pups born at full term. After the 5-month infection period, the parameters were substantially reduced to 29%, 6.20 +/- 0.80 implantation sites, and 5.10 +/- 0.80 pups, respectively. Average testosterone concentrations in serum and testis from control male rats were 8.80 +/- 0.95 ng/ml and 3.88 +/- 0.25 ng/mg protein, respectively. After the 5-month infection period, these levels were reduced to 2.47 +/- 0.31 ng/ml and 1.28 +/- 0.12 ng/mg protein, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Endoscopic lithotripsy of gastric bezoars using a laser-ignited mini-explosive device

This paper reports the successful experiences of in vitro and in vivo studies on endoscopic fragmentation of gastric bezoars using a laser-ignited mini-explosive device. This new technique has been used clinically in 31 patients with gastric bezoars since January 1988. All patients were completely cured without any complication. The relationship between gastric bezoars and ulcers, and the technique of treatment were discussed.

Inhibitory effect of gossypol on human chorionic gonadotropin (hCG)-induced progesterone secretion in cultured bovine luteal cells

Inhibitory effects of gossypol on the female reproductive system have been recently reported. This study investigated a possible site of gossypol action on progesterone synthesis. Bovine luteal cells were cultured with hCG and forskolin in the presence or absence of gossypol. At 10 micrograms/ml, gossypol significantly inhibited hCG- and forskolin-stimulated progesterone secretion and intracellular cAMP formation; at 20 micrograms/ml, gossypol completely abolished the stimulative effect of hCG and forskolin. The results suggest that adenylate cyclase may be a site of gossypol action on steroidogenesis of bovine luteal cells.

[McAb LC-1 against human lung cancer]

Recently Ge et al reported LAC-122, LAC-210 and LAC-163 McAbs against Human non-small cell lung cancer and LSC McAbs against human lung small cell carcinoma. The immunotoxin, composed of McAb LAC-122 conjugated with Ricin A chain has been reported to have the significant cytotoxic effect in vitro on lung adenocarcinoma cell line SPC-A-1 by Tan et al. The LAC-122 alone has no effect on this target cell in the presence of complement from human, rabbit or guinea pig. The tumor associated antigens of human lung cancer have been recognized for many years, but only few reports deal with the common antigens or common epitopes of the lung cancer. From one fusion, 20 hybrids had been observed, all of these culture supernatants could react with target cell by IF. One of them after 4 th cloning, immunoglobulin isotype of the monoclonal antibody thus far obtained belonged to IgM and named to LC-1. Table 1 showed the results of ABC staining of LC-1 with a variety of tumors, normal adult and fetal tissues. From 12 non-small cell lung cancers, including 7 lung adenocarcinoma, 2 lung squamous carcinoma, 3 lung giant cell carcinoma, only one adenocarcinoma gave negative staining. As for 6 small cell lung cancers, all of them showed the positive reaction. It could be also reacted with 11 other tumors.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine receptor in a C2 muscle cell variant is retained in the endoplasmic reticulum

We have examined the properties and intracellular localization of acetylcholine receptors in the C2 muscle cell line and in a variant (T-) that accumulates AChR intracellularly. On immunoblots, the subunit structures of the AChR from wild-type and T- cells were similar except that the gamma and delta subunits of the variant AChR had altered mobilities. Digestion with endoglycosidases H and F demonstrated that this difference results from a failure of high-mannose N-linked oligosaccharides on AChR subunits to be processed to complex forms in the variant. N-linked glycosylation of other proteins in the variant was normal. When examined by immunocytochemistry, the distribution of internal AChR in wild-type cells was consistent with a location both in the endoplasmic reticulum and in the Golgi. Variant cells, however, showed no evidence of Golgi staining. Subcellular fractionation experiments also demonstrated AChR in the Golgi fractions of wild-type cells, but not in those derived from T- cells. We conclude that in T- myotubes most of the AChR fails to be transported out of the endoplasmic reticulum.

A C2 muscle cell variant defective in transport of the acetylcholine receptor to the cell surface

We have previously reported the isolation of variants of the C2 mouse muscle cell line that express reduced amounts of acetylcholine receptors (AChRs) on their surface (Black, R. A., and Hall, Z. W. (1985) Proc. Natl. Acad. Sci. U.S.A. 82, 124-128). One of the variants, T-, makes an approximately normal amount of the AChR but accumulates most of it in an intracellular pool. This pool is stable and does not serve as precursor for surface AChR. Surface levels of insulin receptor and transferrin receptor are normal in T- cells, and a normal proportion of total hemagglutinin is expressed on the surface after infection of the T- variant with influenza virus. Pulse-chase experiments and kinetic analysis show: 1) that T- cells synthesize a normal amount of the alpha subunit but degrade it much more slowly than do wild-type cells; and 2) that newly synthesized alpha subunit is assembled into the AChR at a normal rate. A small fraction of the assembled AChR in T- cells is transported to the surface with normal kinetics, but most of it remains in an internal pool. This variant may provide an important tool for investigation of the factors that regulate AChR assembly and transport to the surface membrane.

Can late abortion be ethically justified?

This paper reviews the practice of late abortion in China and summarizes the arguments for morally justifying the 'one couple, one child' policy.

Developmental changes in lactate dehydrogenase-X activity in young jaundiced male rats

This study was designed to examine the testicular maturation in both jaundiced (jj) and nonjaundiced (Jj) male Gunn rats as indicated by the activity of a testis and sperm-specific enzyme, lactate dehydrogenase-X (LDH-X), and serum testosterone levels. Testicular cytosolic LDH-X activity was determined by oxidation of reduced nicotinamide adenine dinucleotide (NADH). Serum testosterone levels were measured by radioimmunoassay (RIA). Testicular LDH-X activity increased rapidly between 30 and 50 days of age in both Jj and jj Gunn rats. LDH-X activity was significantly lower in the jj Gunn rats at 50 and 60 days of age. Testosterone level was significantly lower in the jj Gunn rats at 50 days of age. LDH-X activity and serum testosterone levels were similar for both genotypes at 180 days of age. The delay of testicular maturation in the jaundiced males seems to be due to lower LDH-X activity and serum testosterone levels.

Characterization of acetylcholine receptor subunits in developing and in denervated mammalian muscle

We have used subunit-specific antibodies to identify and to characterize partially the alpha, beta, gamma, and delta subunits of rat skeletal muscle acetylcholine receptor (AChR) on immunoblots. The alpha subunit of rat muscle is a single band of 42 kDa, whereas the beta subunit has an apparent molecular mass of 48 kDa. Both alpha and beta subunits are glycosylated and contain one or more N-linked oligosaccharide chains that are sensitive to endoglycosidase H digestion. The gamma and delta subunits, on the other hand, each appear as doublets on immunoblots, with apparent molecular masses of 52 kDa (gamma), 48 kDa (gamma') and 58 kDa (delta), 53 kDa (delta'), respectively. In each case, the two bands are structurally related and the lower band is probably the partial degradation product of the corresponding upper band. Each of the four gamma and delta polypeptides is N-glycosylated and contains both endoglycosidase H-sensitive and endoglycosidase H-resistant oligosaccharides. When the AChRs purified from embryonic, neonatal, adult, and denervated adult rat muscles were compared, no differences in the mobilities of alpha, beta, or delta subunits on sodium dodecyl sulfate gels were detected among them, either with or without endoglycosidase treatment. The gamma subunits, which were present in AChRs purified from neonatal, embryonic, or denervated rat muscles, were also identical; no gamma subunit was detected, however, in AChRs of normal adult rat muscle.

Immunological evidence for a change in subunits of the acetylcholine receptor in developing and denervated rat muscle

We used specific antibodies to gamma, delta, and epsilon subunits to characterize acetylcholine receptor (AChR) in extracts and at endplates of developing, adult, and denervated rat muscle. The AChRs in normal adult muscle were immunoprecipitated by anti-epsilon and anti-delta, but not by anti-gamma antibodies, whereas AChRs in denervated and embryonic muscles were precipitated by anti-gamma and anti-delta, but showed little or no reactivity to anti-epsilon antibodies. In immunofluorescence experiments, AChRs at neonatal endplates bound antibodies to gamma or delta, but not epsilon, subunit, whereas those in adult muscles bound antibodies to epsilon or delta, but not gamma, subunit. AChRs at denervated endplates and at developing endplates between postnatal days 9 and 16 bound all three antibodies. We conclude that the distribution of gamma and epsilon subunits of the AChR parallels the distribution of AChRs with embryonic and adult channel properties, respectively.

Gastric processing and emptying of fat

This study was undertaken to determine whether fat leaves the stomach within or bound to the surface of particles of solid food. We studied gastric emptying of fat in 6 human subjects and in 6 dogs with Roux-en-Y duodenojejunostomies so that chyme leaving the stomach could be collected free of bile and pancreatic enzymes. Humans were studied with a duodenal multilumen tube so that phase-specific, nonabsorbed markers in the meal could be tracked with corresponding, phase-specific markers perfused into the duodenum. In this way, we observed the separate time-courses of gastric emptying of the aqueous and solid phases, as well as the extracellular fat (ECF) and intracellular fat (ICF) phases of the meal. In the dogs, all chyme leaving the stomach was collected from a Roux-en-Y fistula and was analyzed directly for aqueous, solid, ECF, and ICF markers in the meal. In both the humans and the dogs, the aqueous phase emptied promptly, whereas the solid, ECF, and ICF phases emptied together, in parallel, after an initial lag. In humans, 22% of the ECF versus 51% of the ICF (p less than 0.02) emptied on or in the solid food particles. In dogs, 81% of the ECF emptied as an oil, 13% emptied on the solid particles, and only 6% emptied as a stable, aqueous emulsion. Sixty-six percent of the ICF emptied in the solid food particles, 20% as a stable, aqueous emulsion, and 14% as an oil. We conclude that most of the ICF empties within the solid food phase, whereas most of the ECF empties as an oil phase.

Effects of viscosity and fluid outflow on postcibal gastric emptying of solids

It is known that the food-filled stomach retains large spheres or pieces of food, allowing the passage of food particles or of plastic spheres with diameters mainly below 2 mm. We have recently shown that spheres having densities greater or less than water emptied from the food-filled canine stomach more slowly than spheres of the same diameter with a density of 1. Thus, hydrodynamics seem to govern gastric emptying of spheres. The present studies were undertaken to determine how altering other hydrodynamic factors, viscosity and velocity of fluid outflow, might affect gastric sieving. Ten mongrel dogs were prepared with chronic duodenal fistulas, which allowed collecting and measuring of emptied spheres and food. The dogs were fed a standard meal of 75 g of steak plus 25 g of 99mTc-labeled chicken liver. Immediately afterward, 50 3.2-mm Teflon spheres were instilled into the stomachs along with 200- or 800-ml volumes of saline or saline plus guar (a viscous polysaccharide). Whether 200- or 800-ml volumes were instilled, the guar significantly sped the emptying of the spheres. Fluid outflow was twice as fast after the 800-ml instillates, but the faster outflow with the 800 ml of saline did not speed emptying of spheres. With the guar instillates, the faster outflow slightly sped the emptying of the spheres and significantly increased the diameter of emptied particles of 99mTc-labeled chicken liver. We conclude that meal viscosity significantly affects gastric sieving.

Effects of gossypol on the estrous cycle and ovarian weight in the rat

The effect of subcutaneously injected gossypol on the estrous cycle and ovarian weights in rats was examined. Daily injections of 5 or 10 mg gossypol/kg/day for 20 days significantly reduced the ovarian weights by 32% and 29%, respectively. Injections of 0.1 and 1.0 mg gossypol/kg/day had no significant effect on ovarian weight. Similarly, ovarian weights were significantly reduced by 37% when hemi-ovariectomized animals were injected with 10 mg gossypol/kg/day for 15 days whereas those of control animals increased in weight by 15%. Animals receiving 5 or 10 mg gossypol/kg/day essentially remained in diestrus by the 15th or the 10th day of injections, respectively. No significant change was found in the liver, adrenal gland or body weight of gossypol-treated rats.

The effects of a myasthenic serum on the acetylcholine receptors of C2 myotubes. I. Immunological distinction between the two toxin-binding sites of the receptor

We have examined the effect of a serum from a patient with myasthenia gravis on the binding of alpha-bungarotoxin (alpha-BuTx) to the acetylcholine receptors (AChRs) of a mouse muscle cell line, C2. After a 2-hr incubation, antibodies in the serum reduced toxin binding to C2 myotubes to a maximal extent of approximately 50%. The degradation of surface AChRs could account for the loss of only 5% of sites during the incubation; the remainder, therefore, must have been lost by blockage of binding. To investigate whether the antibodies blocked specifically one of the two toxin-binding sites that each AChR possesses, we used an analysis based on that of Sine, S. W., and P. Taylor, [1981) J. Biol. Chem. 255: 10144-10156). Although the two sites could not be distinguished by their rates of binding of alpha-BuTx, d-tubocurarine (dTC) inhibition of the initial rate of toxin binding revealed that the sites had affinities for dTC that differed by approximately 30-fold. Incubation with the myasthenic antibodies reduced the number of high affinity dTC sites, without affecting those of low affinity. We conclude that the two toxin-binding sites of the AChR are immunologically distinct.

The effects of a myasthenic serum on the acetylcholine receptors of C2 myotubes. II. Functional inactivation of the receptor

We have investigated the effect of antibodies from a myasthenic serum on the physiological properties of acetylcholine receptors (AChRs) in myotubes of a mouse muscle cell line, C2. The antibodies in this serum blocked the binding of 125I-alpha-bungarotoxin to the myotubes to an extent of about 50%. The antibodies also inhibited the increase in 22Na influx caused by carbamylcholine (CARB). At a concentration of antibody that blocked about 50% of toxin binding, greater than 80% of the AChR-mediated 22Na influx was blocked. The apparent KD for CARB, estimated from the dose-response curve for 22Na influx, was unaffected. The effect of the antibodies was further examined by patch-clamp recording. In greater than 30% of the patches from antibody-treated cells, no channel activity in response to acetylcholine was seen; in contrast, every patch from control cells showed activity. The channels that were seen after antibody treatment were indistinguishable from those seen in normal cells, both in their single-channel conductance and in the kinetic constants used to describe channel opening and closing. We conclude that the antibodies in this serum inhibit the functional response of AChRs in C2 myotubes to acetylcholine and do so by inactivating individual receptors.