Membrane excitability expressed in human neuroblastoma cell hybrids

The voltage-sensitive Na+ channel is responsible for the action potential of membrane electrical excitability in neuronal tissue. Three methods were used to demonstrate the presence of neurotoxin-responsive Na+ channels in two hybrid cell lines resulting from the fusion of excitable human neuroblastoma cells with mouse fibroblasts. Only one of the two electrically active hybrid cell lines maintained the sensitivity of the neuroblastoma parent to tetrodotoxin (TTX). The other hybrid, although electrically active, was not responsive to TTX or scorpion venom. Comparisons of the patterns of expression of membrane excitability and of chromosome complements in these human neuroblastoma cell hybrids suggest that the phenotype of membrane excitability is composed of genetically distinct elements.     

Suppression of the rotifer Polyarthra remata by the omnivorous copepod Tropocyclops extensus: predation or competition

Indirect evidence from observations in the field suggested thata common and often abundant cyclopoid copepod, Tropocyclopsextensus, despite its small size (0.5 mm) and largely algaldiet, is an important predator of the rotifer Polyarthra remata.Laboratory experiments showed that copepodids and adults, butnot nauplii, markedly suppressed the population growth of thisrotifer. The suppression could be attributed entirely to predation,rather than to exploitative competition for shared food resourcesor to interference. Mortality rates predicted from a separatefeeding-rate experiment weresufficient to account for the declinein population size observed in the Tropocyclops treatment ofculture experiments. Also, monitoring the availability of cryptomonadfood in treatments with and without Tropocyclops throughoutthese experiments showed that cryptomonad densities always remainedhigh and were just as high or significantly higher in the copepodtreatments. Furthermore, direct videographic observations ofP. remata from cultures with and without Tropocyclops demonstratedno significant differences in swimming velocity, tendency todeviate from a straight-line path, or frequency and length ofspontaneous escape responses. Per capita ingestion rates ofT. extensus on P. remata varied from 2 to 8 day^-1, were significantlyhigher for adult females than adult males or copepodids V, andincreased significantly with rotifer density. A tendency ofcopepods to have higher ingestion rates on young than adultrotifers was not significant. Copepods cultured since birthwith cryptomonads and P. remata ate significantly fewer rotifersthan those cultured only with cryptomonads; this may be explainedby a more sated condition of the former and provided no evidencefor the idea that previous experience with this rotifer mightincrease predation efficiency. The results show that T. extensusin natural communities has the potential to deplete naturalpopulations of susceptible rotifer prey. Accordingly, it mayshift the species structure of rotifer assemblages in favourof resistant species, and provide selection pressure for avoidanceresponses.     

Impact d'une pollution urbaine sur la partie zooplanctonique d'un systeme neitique (Marseille - Cortiou)

Sewage of Marseilles' main outfall permanently pollutes a large coastal area centered around Cortiou, south of the city. In order to study the impact of that urban pollution on the zooplankton, more than 200 samples were collected between 1977 and 1981, according to several sampling strategies.Quantitatively, the study area showed a rather poor zooplankton. The more important populations were encountered near Cortiou, the non-perturbated reference point with lowest abundance of organisms. Sampling sites located near the outfall are sometimes azoic. Qualitatively, the observed communities are not characteristic of a heavily polluted environment, but correspond to an impoverished neritic community. In the more polluted area, the community is organized around the copepods Clausocalanus sp., Paracalanus sp. and Oithona helgolandica, and a group of less important species (Oithona nana and the cladoceran Evadne spinifera). Centropagidae, Coryceidae, Onceidae, but also Chaetognathians, Fritilliarins and the meroplanktonic larvae are more frequently encountered in clean water. Community structure is higher during the cold months than summer. The latter period frequently shows a disorganized zooplankton. In most situations, the copepod Acartia clausi plays a minor role in the structural definition of the communities.The variations observed seem largely independent of the parameters reflecting pollution intensity. Stress integration, in relation with the anterior community history (intensity of contact with polluted water, trophic potential of the area) seem to be the main regulator factors.

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Impact d'une pollution urbaine sur la partie zooplanctonique d'un systeme neitique (Marseille - Cortiou)

Resumé Le rejet permanent du grand émissaire de Marseille (5 m³, sec^–1) perturbe considérablement, par son importance, le système néritique du secteur de Cortiou. Afin d'approcher l'impact de cette pollution sur la partie zooplanctonique du système, plus de 200 prélèvements, concernant l'hydrologie et le plancton, ont of é\'t é réalises entre 1977 et 1981, selon différentes strategiés d'échantillonnage (suivi de masse d'eau, radiales, réseaux).Quantitativement on observe, sur l'ensemble de la zone étudiée, une abondance générale en zooplancton moyenne, voire faible. Les effectifs les plus importants se rencontrent cependant dans la cuvette de Cortiou, alors que le point de référence considéré comme non perturbé présente les effectifs les plus faibles. Les stations situées face à l'égout sont parfois azoïques.Qualitativement les peuplements ne paraissent pas trés caractéristiques d'un secteur pollué mais correspondent plutôt à un appauvrissement du peuplement néritique. Dans le secteur le plus pollué, la composition spécifique varie au cours du temps autour d'une communauté composée d'un groupe important avec Clausocalanus sp., Paracalanus sp., Oithona helgolandica et d'un groups de taxons moins fréquents représentés par des larves méroplanctoniques, Oithona nana et Evadne spinifera, tandis que les coryceidés, onceidés, Centropages typicus, chaetognathes et fritillaires se retrouvent plus fréquemment en eaux propres. La structure des populations est plus importante en période froide qu'en période chaude, période durant laquelle la communauté planctonique est fortement désorganisée. Paradoxalement Acartia clausi joue un rôle assez secondaire dans la définition structurelle de la communauté.Les fluctuations observées paraissent cependant peu liées à des paramètres reflétant l'intensité de la pollution. L'intégration du stress, en relation avec l'histoire antérieure de la communauté (intensité et durée du contact avec la nappe de dilution, potentialités trophiques) semblent ainsi prépondérantes.

     

Dinucleoside tetraphosphate variations in cultured tumor cells during their cell cycle and growth

Asynchronous and synchronized cultures of A549 and HTC cells were used to detect possible, cell cycle or cell density specific variations in the intracellular pools of dinucleoside tetraphosphates (Ap4X). No important variations of the nucleotide pools were observed during cell growth. When HTC cells were released from mitotic arrest, a decrease by a factor of N3 Ap4X and ATP levels was observed when the cells entered the G1 phase. This decrease is essentially due to cell doubling. When A549 cells were released from an arrest at the G1/S boundary, the nucleotide pool size increased slightly during the G2 phase just before mitosis. This result is in agreement with both earlier data from our laboratory and the observed decrease in Ap4X pool after release from mitotic-arrested HTC cells. These results suggest that the Ap4X and ATP pools are only subjected to very small variations during the cell cycle, essentially in the G2 phase and after mitosis.     

The diagnosis of short penis as a cause of impotentia coeundi in bulls

Short penis condition was diagnosed as the cause of impotentia coeundi in 10 bulls, aged 2.5 to 5 yr. The diagnosis was based on observation of service attempts, measurement of the extended penis, and elimination of other causes of impotence. Measurements of the penis were made under general inhalation anesthesia or pudendal nerve block. These measurements were then compared with those of 10 control bulls, matched for age and breed and having no history of impotence; the latter measurements were likewise obtained under general anesthesia, pudendal nerve block or sedation. with propionyl promazine. Similar measurements were obtained from 10 yearling bulls under propionyl promazine sedation. Measurements obtained under general anesthesia or pudendal nerve block in the same bull were usually similar and repeatable, while phenothiazine tranquillization produced incomplete and variable relaxation of the retractor penis muscles. The dimension best correlated with impotence due to short penis was the distance from the tip of the extended penis to the preputial orifice in its resting position. In 10 bulls in which short penis was diagnosed, this distance was 10 to 22 cm, while in 10 control bulls with no history of impotence it was 25 to 42 cm. The distances from the tip of the extended penis to the preputial reflection (fornix) and to the neck of the scrotum were also shorter in affected than in control bulls. Although observation of service ability remains the cornerstone of diagnosis of short penis, a presumptive diagnosis can be made if penile protrusion of less than 25 cm can be obtained in an adult bull under general anesthesia or pudendal nerve block. Phenothiazine tranquillization is suitable for screening examinations but not for definitive diagnosis.