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B A Block

Publications and source records attributed to B A Block.

27 records · Page 2Linked to original sources
PubMed1992

Direct sequencing of mitochondrial DNA detects highly divergent haplotypes in blue marlin (Makaira nigricans).

We were able to differentiate between species of billfish (Istiophoridae family) and to detect considerable intraspecific variation in the blue marlin (Makaira nigricans) by directly sequencing a polymerase chain reaction (PCR)-amplified, 612-bp fragment of the mitochondrial cytochrome b gene. Thirteen variable nucleotide sites separated blue marlin (n = 26) into 7 genotypes. On average, these genotypes differed by 5.7 base substitutions. A smaller sample of swordfish from an equally broad geographic distribution displayed relatively little intraspecific variation, with an average of 1.3 substitutions separating different genotypes. A cladistic analysis of blue marlin cytochrome b variants indicates two major divergent evolutionary lines within the species. The frequencies of these two major evolutionary lines differ significantly between Atlantic and Pacific ocean basins. This finding is important given that the Atlantic stocks of blue marlin are considered endangered. Migration from the Pacific can help replenish the numbers of blue marlin in the Atlantic, but the loss of certain mitochondrial DNA haplotypes in the Atlantic due to overfishing probably could not be remedied by an influx of Pacific fish because of their absence in the Pacific population. Fishery management strategies should attempt to preserve the genetic diversity within the species. The detection of DNA sequence polymorphism indicates the utility of PCR technology in pelagic fishery genetics.

Amino Acid Sequence↗
PubMed1991

Activities of key metabolic enzymes in the heater organs of scombroid fishes.

Maximal in vitro activities of key metabolic enzymes were measured in brain and eye heaters of five species of scombroid fishes. Istiophorid billfishes (blue marlin, striped marlin and Mediterranean spearfish), xiphiid billfishes (Pacific and Mediterranean stocks) and a scombrid fish (butterfly mackerel) were included in the analysis. Our main objectives were (1) to assess the maximum possible substrate flux in heater tissue, and (2) to determine what metabolic substrates could fuel heat production. Heater tissue of all scombroids examined showed extremely high oxidative capacity. Activities of citrate synthase, a commonly measured index of oxidative metabolism, included the highest value ever reported for vertebrate tissue. In most billfishes, citrate synthase activities were similar to or higher than those found for mammalian cardiac and avian flight muscle. Marker enzymes for aerobic carbohydrate metabolism (hexokinase) and fatty acid metabolism (carnitine palmitoyltransferase and 3-hydroxyacyl-CoA dehydrogenase) also displayed extraordinarily high activities. Activities of carnitine palmitoyltransferase measured in heater organs were among the highest reported for vertebrates. These results indicate that heat production could be fueled aerobically by either lipid or carbohydrate metabolism. Inter- and intraspecifically, heater organs of fishes from the colder Mediterranean waters had a higher aerobic capacity and, hence, a greater heat-generating potential, than fishes from the warmer waters of the Pacific. This difference may be attributed to different thermal environments or it may result from allometry, since fishes caught in the Mediterranean were considerably smaller than those caught in the Pacific.

Animals↗
PubMed1988

The structure of the membrane systems in a novel muscle cell modified for heat production.

A thermogenic organ, modified from an eye muscle, warms the brain and eyes of several oceanic fish. The extraocular muscles associated with thermogenesis are composed of modified muscle cells that are structurally distinct from all other types of muscle previously described. In "heater" cells, contractile filaments are virtually absent and the cell volume is packed with mitochondria and smooth membranes. Freeze-fracture studies and negative staining of microsomal fractions treated with vanadate indicate that most of the membrane system of heater cells has a high Ca2+-ATPase density and is equivalent to skeletal muscle sarcoplasmic reticulum (SR). High voltage electron micrographs of heater cells infiltrated with the Golgi stain demonstrate that the cells also have an extensive transverse tubule system with a complicated three-dimensional structure. Junctional regions between transverse tubules and SR occur in the heater cell and contain feet protein. Activation of thermogenesis in heater cells may occur through the same protein components involved in excitation-contraction coupling and appears to be associated with the ATP-dependent cycling of calcium at the SR.

Animals↗
PubMed1988

Structural evidence for direct interaction between the molecular components of the transverse tubule/sarcoplasmic reticulum junction in skeletal muscle.

The architecture of the junctional sarcoplasmic reticulum (SR) and transverse tubule (T tubule) membranes and the morphology of the two major proteins isolated from these membranes, the ryanodine receptor (or foot protein) and the dihydropyridine receptor, have been examined in detail. Evidence for a direct interaction between the foot protein and a protein component of the junctional T tubule membrane is presented. Comparisons between freeze-fracture images of the junctional SR and rotary-shadowed images of isolated triads and of the isolated foot protein, show that the foot protein has two domains. One is the large hydrophilic foot which spans the junctional gap and is composed of four subunits. The other is a hydrophobic domain which presumably forms the SR Ca2+-release channel and which also has a fourfold symmetry. Freeze-fracture images of the junctional T tubule membranes demonstrate the presence of diamond-shaped clusters of particles that correspond exactly in position to the subunits of the feet protein. These results suggest the presence of a large junctional complex spanning the two junctional membranes and intervening gap. This junctional complex is an ideal candidate for a mechanical coupling hypothesis of excitation-contraction coupling at the triadic junction.

Animals↗
PubMed1987

Evidence for a junctional feet-ryanodine receptor complex from sarcoplasmic reticulum.

Heavy sarcoplasmic reticulum vesicles, labelled with the Ca2+ release channel probe [3H]ryanodine, were solubilized in detergent, then centrifuged through sucrose gradients. A single peak of ryanodine binding activity was observed with an apparent sedimentation coefficient of 30S. Electron microscopy of the peak fraction showed disk structures of 25-28 nm diameter and 10 nm thickness. Proteins specifically enriched in the peak fraction were the Mr 160,000 and 260,000 and junctional feet proteins (Mr 320,000 and 300,000). This suggests that the feet proteins and ryanodine receptor may be specifically associated into a large oligomeric complex comprising subunits of Mr 160,000-320,000.

Alkaloids↗
PubMed1986

Structure of the brain and eye heater tissue in marlins, sailfish, and spearfishes.

Marlins, sailfish, and spearfishes have a heat-producing tissue beneath the brain and adjacent to the eyes. This tissue warms the brain and eyes while the rest of the body remains at water temperature. The heater tissue is derived from the superior rectus eye muscle. Only a portion of this eye muscle contains normal skeletal muscle tissue; the rest consists of the modified muscle tissue that is associated with heat production. The heat-producing portion is supplied with blood through a countercurrent heat exchanger that originates from the carotid artery. The vascular rate prevents the heat being produced by the tissue from being dissipated at the gill. An unusual circulatory supply to the eyes and brain is associated with the presence of the heater tissue in these fishes.

Animals↗
PubMed1985

Warm brain and eye temperatures in sharks.

Temperatures in the brain and eyes of mako and porbeagle sharks (Lamnidae) are 5 degrees C warmer than the water while the brain and eye temperatures in six other species of pelagic sharks are within 0.1 degrees C of water temperature. An orbital rete mirabile is present in the porbeagle and mako sharks but absent in the cranial vasculature of eleven other species of pelagic sharks. The orbital rete in the head of the porbeagle and mako sharks acts as a heat exchanger which conserves metabolic heat and raises the local tissue temperatures. This brain and eye warming system should buffer the central nervous system from the effects of rapid temperature change. Warming of the retina may improve the visual sensitivity of these active predators.

Animals↗
PubMed1982

Fluvoxamine maleate, a serotonergic antidepressant; a comparison with chlorimipramine.

1. Fluvoxamine is a potent serotonin re-uptake inhibitor, with little or no noradrenergic or anticholinergic activity. 2. The results of three studies using an almost identical protocol with a prospectively randomized, double-blind design comparing fluvoxamine and chlorimipramine are presented. 3. In a population of 98 subjects suffering from a variety of depressive conditions, there was a marked improvement over four weeks in both groups. dosage was maintained between 150 and 300 mg per day. 4. There were no changes of clinical importance in vital signs, hematology or biochemistry, but pulse rates increased in the chlorimipramine group. 5. There were fewer concurrent signs and symptoms in the fluvoxamine group, especially those attributable to anticholinergic activity.

Antidepressive Agents↗