Seventeen clones of the ciguatera‐causing dinoflagellate Gambierdiscus toxicus Adachi and Fukuyo were acclimated to the same environments over several months. Significant variance components were detected between non‐acclimated and acclimated cultures for cell potencies, yields and reproduction rates. The resultant variance in acclimated potencies among clones was statistically significant (P < 0.0001), indicating that potency can be used for genetic comparisons. However, cell potency differences for a clone of G. toxicus in the acclimated vs. non‐acclimated phases can exceed genetic differences between clones. This stresses the need for a rigorous acclimation process. Caribbean isolates of G. toxicus were inherently more toxic than isolates from other areas. One Caribbean clone yielded 55 × 10−4 mu (mouse units)·cell−1 whereas clones Bermuda, the Bahamas, and Florida ranged from only 1.8 × 10−4 mu·cell−1 to a maximum of 19.8 × 10−4 mu·cell−1. Toxicity decreased with increasing latitude (r =–0.819, P < 0.01), indicating that environmental differences probably influenced the potencies. A comparison of acclimated reproduction rates at four light intensities also indicated that genetic differences among clones existed. The resulting reproduction rate/light slopes overlapped, indicating that the clones may be adapted to specific light regimes.
The dinoflagellate toxin maitotoxin (MTX) stimulated 45Ca2+ uptake in cultured NG108-15 neuroblastoma x glioma cells. Depolarizing stimuli (e.g., 50 mM K+) produced an immediate stimulation in Ca2+ uptake, whereas that produced by MTX One of the most important aspects of research on voltagesensitive sodium channels (VSNaC) has been the discovery and development of chemical probes that selectively alter different facets of channel function (1). Thus, toxins such as tetrodotoxin (TTX), batrachotoxin (BTX), and scorpion venom have been shown to interact with separate sites on the channel molecule (2). These toxins have been invaluable in studies directed at isolating the channel molecule and in understanding its properties at a molecular level. Clearly, similar agents would be helpful in advancing our understanding of other channels, such as those for potassium and calcium.Maitotoxin (MTX) is a water-soluble toxin of unknown structure isolated from the poisonous dinoflagellate Gambierdiscus toxicus (3). It is one of the entities responsible for the syndrome known as ciguatera poisoning, which is common in tropical and subtropical areas. The purified toxin has a positive inotropic effect (4), contracts smooth muscle (5, 6), stimulates transmitter release from sympathetic neurons (6) and cultured PC12h pheochromocytoma cells (7,8), and releases prolactin from primary pituitary cultures (9). It has been suggested that MTX is an "activator" of voltage-sensitive calcium channels (VSCC) (5-9). However, no experimental data have been obtained that directly examine the effect of MTX on VSCC.We have previously demonstrated that several cell lines including the neuroblastoma x glioma hybrid NG108-15 express a type of VSCC when grown under the appropriate conditions (10). The pharmacology of these channels has been characterized in detail (10). They appear to be extremely similar to those occurring in smooth muscle. Thus, they are blocked by nanomolar concentrations of dihydropyridines, such as nifedipine, and are activated by the novel dihydropyridines BAY K8644 and CGP 28392 (10, 11). In the present series of studies, we have investigated the interaction of MTX with VSCC in these cultured neuronal cells. Ca2+ Uptake Studies. 45Ca2+ uptake studies were carried out exactly as described by Freedman et al. (10). Briefly, NG108-15 cells were grown as monolayers in 5% C02/95% air in Eagle's minimum essential medium supplemented with 10% fetal bovine serum and 2 mM glutamine. Cells were subcultured onto 60-mm tissue culture plates. To induce cellular differentiation, growth medium was supplemented with 10 ,M prostaglandin E1 and 50 AM 3-isobutyl-1-methylxanthene. Supplemented medium was replaced every 2 days or when required. 3T3 fibroblasts were cultured in Dulbecco's modified Eagle's medium containing 10% fetal bovine serum. During the assay, tissue culture plates were supported in an open air water bath at 37°C. Cells were incubated for 5 min at 37°C. The uptake of 45Ca2+ was measured for increasing periods of time in...
Seventeen clones of the toxic, epiphytic‐benthic dinoflagellate Prorocentrum lima (Ehrenberg) Dodge isolated from three separate sites on the reef flats of Heron Island, Australia, were acclimated under the same set of environmental conditions. Morphological features examined for each clone included cell surface configuration, size, and dry weight. Physiological and biochemical features determined for each clone included reproduction rates, pigments (chlorophyll a, chlorophyll c2, peridinin, and other xanthophylls), toxins (okadaic acid and methyl‐okadaic acid), and macromolecular compounds (total protein, lipid, and carbohydrate). Variation in morphological features and reproduction rates of clones within and between sites was minimal and not significant. Also, variation in biochemical features within an individual site was low, but pronounced differences existed among sites, the most notable of which was toxin content (okadaic acid and methyl‐okadaic acid). The greatest difference in biochemical features was between clones isolated from the southern site and clones isolated from the northern and southeastern sites. Results of a cluster analysis of clonal characters support the view that these two groups represent distinct genotypes. We suggest that these groups originated from separate seed sources and that the genetic integrity of each is maintained through asexual reproduction.
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