Fatty acid incorporation increases the affinity of muscarinic cholinergic receptors for agonists

Incorporation of unsaturated fatty acids into membrane fragments from rat brain cortex and medulla pons selectively increased the affinity of the muscarinic agonist, carbamylcholine. The affinity and number of binding sites for the labeled antagonist, N-[3H]methyl-4-piperidyl benzilate was unchanged. The effect on agonist binding was most prominent in the cortex, in which carbamylcholine IC50 values were decreased up to 5-fold. Selectivity of the effect was observed with fatty acids of chain length 18-20 carbons, unsaturation in position 11-12, and a cis conformation of the double bond being most effective. The effects of fatty acids on agonist binding were due primarily to alterations in the affinity constants for the binding reaction, with minor increases in the proportion of high-affinity sites. Transition metals selectively increased the percentage of high-affinity sites in the cortex, but in cis-vaccenic-acid-treated membranes more than additive effects of the metal were observed; both were reversed by GTP. GTP also reversed binding parameters in cis-vaccenic-acid-treated medulla membranes to control level. We conclude that the primary effect of the active fatty acids is to alter the thermodynamic properties of muscarinic agonist binding without markedly inducing interconversion.     

Segregation analysis of schizophrenia and related disorders

Segregation analysis was applied to 79 nuclear families ascertained through chronic schizophrenic probands. Analysis was performed on the diagnosis of schizophrenia alone and on schizophrenia and schizotypal personality disorder (milder phenotype) combined. The models used were the transmission probability model and the mixed model. Because the disease is associated with reduced fertility, all likelihoods were calculated conditional on parental phenotypes. However, compatibility of the mating-type distribution predicted by each model with the observed was also examined. In all analyses, results suggested consistency with genetic transmission. In the analysis of schizophrenia alone, discrimination among models was difficult. In the analysis including the milder phenotypes, all single-locus models without polygenic background were excluded, while pure polygenic inheritance could not be eliminated. The polygenic model also gave good agreement with supplementary observations (lifetime disease incidences, mating-type distribution, and monozygotic twin concordance). The estimated components of variance for the polygenic model were: polygenes (H) 81.9%; common sib environment (B) 6.9%; random environment (R) 11.2%. Although the polygenic model was parsimonious, segregation analysis and the supplementary observations were also consistent with a mixed model, with a single major locus making a large contribution to genetic liability. Such a locus is more likely to be recessive than dominant, with a high gene frequency and low penetrance. The most likely recessive mixed model gave the following partition of liability variance: major locus, 62.9%; polygenes, 19.5%; common sib environment, 6.6%; and random environment, 11.0%.     

Genetic Basis of Vi Antigen Expression in Salmonella paratyphi C

Analysis of hybrids formed in a cross between a Salmonella paratyphi C Hfr and an S. typhimurium recipient indicated that the structural genetic determinants of the S. paratyphi C Vi antigen are located closely adjacent to the mel determinant, between this marker and purA. A similar location was indicated for the structural genetic determinants of the S. typhi Vi antigen (the viaB locus) by the results of a mating in which a hybrid S. typhimurium Hfr bearing the S. typhi viaB determinants was used to transfer these genes to an S. typhimurium recipient. Mating experiments with a Vi-antigen-expressing S. typhi Hfr and an S. typhimurium hybrid recipient expressing the Vi antigen of S. paratyphi C yielded no recombinants in which loss of Vi antigen expression occurred, indicating that the chromosomal locus occupied by the genetic determinants of the S. paratyphi C Vi antigen is the same one at which, in S. typhi, the viaB genes reside. Introduction of a mutant S. typhi viaA gene into an S. typhimurium hybrid expressing the Vi antigen, as the consequence of prior receipt of the S. paratyphi C viaB determinants, resulted in that hybrid's loss of Vi antigen expression, demonstrating that the viaA determinant plays a role in Vi antigen expression in S. paratyphi C, as well as in S. typhi. Although the percentages of coinheritance of the viaB and mel determinants in the mating experiments suggested that their linkage is sufficiently close to allow cotransduction by P22, attempts to accomplish this with lysates prepared on S. typhimurium hybrids expressing either S. typhi or S. paratyphi C viaB determinants were not successful.     

A P Nuclear Magnetic Resonance Study of Intracellular pH of Plant Cells Cultivated in Liquid Medium

³¹P nuclear magnetic resonance has been used to study the vacuolar and cytoplasmic pH of Acer pseudoplatanus, Catharanthus roseus, and Glycine max cells grown as cell suspensions. The adaptation of this technique to plant cells grown in liquid medium is described with emphasis on the removal of Mn²⁺ and phosphate from the extracellular medium and on providing the O₂ supply of the cells in the nuclear magnetic resonance tube and the various problems of calibration. Aerobic and anaerobic cells show large differences in their glucose-6-phosphate, their cytoplasmic inorganic phosphate pools, and their cytoplasmic pH. Differences in the relative sizes of the cytoplasmic and vacuolar inorganic phosphate pools have been observed for the three cell strains studied.     

The modelling of a burst-generating neuron with a field-effect transistor analog

An electronic analog that models the burst generating neuronR ₁₅ of theAplysia abdominal ganglion is described. The analog is based on the four branch Hodgkin-Huxley equivalent circuit for a patch of squid axon membrane, with a choice of parameter values appropriate to theAplysia cell membrane. To realize the slow subthreshold oscillations seen in cellR ₁₅ upon exposure to the drug tetrodotoxin (TTX), it was necessary to include two additional conductance branches,g _Na andg _K, to the basic Hodgkin-Huxley circuit. Without these, the analog was capable of generating only action potentials and hence termed the suprathreshold analog. With all six branches operative, bursts very similar to those seen inR ₁₅ were realized, and subsequent inhibition of the Hodgkin-Huxley sodium conductanceg _Na resulted in the desired subthreshold oscillations. The electronic circuitry and the performance of the suprathreshold and complete analog are described. An explanation is offered for the progressive widening of the action potentials within a burst seen inR ₁₅. The analog also simulates the phenomenon of potassium ion accumulation outside the cell membrane during a burst, using a local feedback loop to reduce the potassium equilibrium potential in a manner roughly proportional to the logarithm of the time integral of the outward potassium current. Some consequences of this effect are also discussed.     

Mechanisms involved in parasitic castration: in vitro effects of the trematode Prosorhynchus squamatus on the gametogenesis and the nutrient storage metabolism of the marine bivalve mollusc Mytilus edulis

The mechanisms involved in the parasitic castration of the marine mussel Mytilus edulis by the trematode parasite Prosorhynchus squamatus Odhner, 1905, have been investigated in vitro with two bioassays employing dissociated host tissues. There is no conclusive evidence that P. squamatus affects the secretion of two host neuroendocrine factors, viz., gonial mitosis-stimulating factor and glycogen mobilization hormone, involved in the gametogenesis/nutrient storage cycles of the mussel. In contrast, extracts of P. squamatus sporocysts and cercariae significantly stimulated glycogen mobilization in host glycogen cells and strongly inhibited host gonial mitosis. A gonial mitosis-inhibiting factor (GMIF) was found in the hemolymph of parasitized mussels. The existence of an endogenous GMIF in mantle tissue of uninfected mussels has been demonstrated. This factor appeared to be secreted into the hemolymph during the period of sexual maturity. Whether the parasite acts directly on the host gonia, or by provoking the liberation of this endogenous GMIF, has yet to be ascertained. It would appear, however, that the parasite acts directly on host glycogen cells.     

Protein modules

As the database of protein sequences grows it is becoming apparent that many proteins are constructed from relatively few modular units that appear many times. Determination of the three-dimensional structure of such modules by NMR has been possible due to their production in relatively large quantities by recombinant DNA techniques. The knowledge gained about the structure of individual modules can then be used to predict their properties in a variety of intact proteins.     

Production and specificity of monoclonal antibodies against calmodulin from Dictyostelium discoideum

Monoclonal antibodies were raised against calmodulin purified from Dictyostelium discoideum. To increase its antigenicity, the calmodulin was conjugated to keyhole limpet hemocyanin; mice were immunized with the conjugate. Hybridomas producing antibodies against calmodulin were identified by screening culture supernatants with calmodulin coupled to bovine serum albumin. The specificity of antibodies from hybridoma culture supernatants was tested by Western blot of Dictyostelium cell lysates. For the purpose, methods were developed that permitted sensitive detection of calmodulin bound to membranes. The key elements of the blotting protocol were used of PVDF membrane, transfer conducted in phosphate buffer, and glutaraldehyde fixation after transfer. These methods permitted detection of as little as 0.1 ng of calmodulin spotted directly onto the membrane, or 10 ng transferred from an SDS polyacrylamide gel. Ten calmodulin-specific antibodies were identified; most of these reacted preferentially with the calcium-containing form of Dictyostelium calmodulin. Several of the monoclonal antibodies cross-reacted with calmodulin from bovine brain.