The diacylglycerol analogue, 1,2-sn-dioctanoylglycerol, induces an increase in cytosolic free Ca2+ and cytosolic acidification of T lymphocytes through a protein kinase C-independent process.

In this paper, we demonstrate that low concentrations (0.5-2.5 microM) of 1,2-sn-dioctanoylglycerol (DiC8), a potent diacylglycerol used in many previous studies to probe the role of protein kinase C (PKC) in cell activation, cause cytosolic alkalinization of human, mouse and pig T lymphocytes through PKC-mediated activation of the Na+/H+ antiport. However, at higher concentrations (greater than or equal to 12.5 microM), the effect on cytosolic pH (pHi) is reversed, resulting in a marked cytosolic acidification, followed by a gradual return of pHi to baseline values. DiC8 also induces marked changes in cytosolic free calcium concentrations ([Ca2+]i), initially by releasing calcium from intracellular stores, followed by a net transmembrane influx of calcium. The DiC8-induced cytosolic acidification, the resultant return to baseline pH and the increase in [Ca2+]i are independent of activation of PKC. Unlike many other agents which increase [Ca2+]i, DiC8 does not induce phosphatidylinositol hydrolysis with the resultant production of inositol phosphates. Other compounds known to activate PKC, including the closely related diacylglycerol analogues, 1,2-sn-dihexanoylglycerol and 1,2-sn-didecanoylglycerol, phorbol esters and mezerein, did not induce changes in [Ca2+]i or cytosolic acidification in T lymphocytes. Thus the action of DiC8 on intact lymphocytes is different from that of phorbol esters and other diacylglycerols, and is specific to the length of the acyl chains. Because changes in [Ca2+]i are often associated with cell proliferation and cell differentiation, some effects of DiC8 on intact cells may be a consequence of changes in [Ca2+]i.     

Decreased atrial natriuretic factor receptors and impaired cGMP generation in glomeruli from the cardiomyopathic hamster

To determine a possible basis for the decreased action of atrial natriuretic factors (ANF) in congestive heart failure, we compared the cardiomyopathic hamster (CMH) in frank congestive failure, and the age-matched, normal, F1B strain of Golden Syrian Hamsters. Scatchard analysis of competitive binding studies revealed two classes of glomerular receptors. The CMH exhibited decreased binding overall and a markedly decreased number of high affinity receptors but comparable receptor affinity compared to the F1B. In contrast, the low affinity receptor population in the CMH had a much greater affinity compared to the F1B while receptor number was similar. Plasma ANF levels were substantially elevated in the CMH compared to the F1B and in-vitro generation of cGMP was significantly lower in the CMH. Such abnormalities could contribute to the resistance to ANF in this disease.     

Use of a synthetic dodecapeptide (malantide) to measure the cyclic AMP-dependent protein kinase activity ratio in a variety of tissues.

1. The cyclic AMP-dependent protein kinase activity-ratio assay was investigated by comparing histone and a synthetic peptide, malantide [Malencik & Anderson (1983) Anal. Biochem. 132, 32-40], as substrates. 2. In several tissues the activity ratio was higher when assayed with histone as the substrate; this result was obtained in control tissues and also in those incubated with agents known to increase cyclic AMP. The effect of these agents to increase the activity ratio was more clearly demonstrated with malantide. 3. The higher activity ratios observed with histone are due to: (a) measurement of phosphorylation not catalysed by cyclic AMP-dependent protein kinase; (b) activation of cyclic AMP-dependent protein kinase by histone during the assay. 4. When tissues were homogenized in buffers without NACl, lower activity ratios were found, owing to the catalytic subunit being artifactually removed from the supernatant. 5. We conclude that the measured activity ratio more faithfully reflects that in the tissue when NaCl is included in the homogenization buffer and malantide is used in the assay. This was confirmed in experiments where cyclic AMP-dependent protein kinase was added to the tissue before homogenization, and no dissociation of the exogenous enzyme was observed.     

Neuron-specific and state-specific differences in calcium homeostasis regulate the generation and degeneration of neuronal architecture

Many stimuli (e.g., neurotransmitters and electrical activity) regulate neuromorphogenesis by changing intracellular calcium. The ionophore A23187 was employed as a receptor-independent method to investigate neuronal calcium homeostasis. Distinctive neuron-specific (B5 versus B19) and state-specific (growing versus non-growing) differences in calcium homeostasis were observed in cultured identified Helisoma neurons. Fura-2 studies revealed that A23187 induced a transient rise in intracellular calcium in growing neurons B5 but a sustained rise in growing neurons B19. In stable-state (non-growing) cells A23187 evoked only a transient calcium rise. Both neuron-specific and state-specific differences in calcium homeostasis were dependent on extracellular sodium. Morphological studies also indicated that such differences in calcium-regulatory capacity can have profound consequences on the generation and degeneration of neuronal architecture.     

Haemogregarina georgianae n. sp., a new haemogregarine parasite from the Antarctic teleost Parachaenichthys georgianus

Haemogregarina georgianae n. sp. occurs frequently in the bathydraconid teleost Parachaenichthys georgianus from the western Antarctic portion of the Southern Ocean. The haemogregarine and its developmental stages in the vertebrate have been found in erythrocytes of the fish: both microschizogony and macroschizogony have been seen in fish caught during the austral summer. Morphological evidence suggests the merozoites from macroschizogony give rise to the microschizont, and that the microschizont merozoites give rise to gametocytes. Comparison of H. georgianae with other haemogregarines known from teleosts shows that it has a previously undescribed morphology.     

Characterization of Neurotensin Binding Sites in Intact and Solubilized Bovine Brain Membranes

Analysis of the equilibrium binding of [3H]-neurotensin(1-13) at 25 degrees C to its receptor sites in bovine cortex membranes indicated a single population of sites with an apparent equilibrium dissociation constant (KD) of 3.3 nM and a density (Bmax) of 350 fmol/mg protein (Hill coefficient nH = 0.97). Kinetic dissociation studies revealed the presence of a second class of sites comprising less than 10% of the total. KD values of 0.3 and 2.0 nM were obtained for the higher and lower affinity classes of sites, respectively, from association-dissociation kinetic studies. The binding of [3H]neurotensin was decreased by cations (monovalent and divalent) and by a nonhydrolysable guanine nucleotide analogue. Competition studies gave a potency ranking of [Gln4]neurotensin greater than neurotensin(8-13) greater than neurotensin(1-13). Smaller neurotensin analogues and neurotensin-like peptides were unable to compete with [3H]neurotensin. Stable binding activity for [3H]neurotensin in detergent solution (Kd = 5.5 nM, Bmax = 250 fmol/mg protein, nH = 1.0) was obtained in 2% digitonin/1 mM Mg2+ extracts of membranes which had been preincubated (25 degrees C, 1 h) with 1 mM Mg2+ prior to solubilization. Association-dissociation kinetic studies then revealed the presence of two classes of sites (KD1 = 0.5 nM, KD2 = 3.6 nM) in a similar proportion to that found in the membranes. The solubilized [3H]-neurotensin activity retained its sensitivity to cations and guanine nucleotide.     

An electrophoretic and biometric study of Arctic charr, Salvelinm alpinus (L.), from ten British lakes

Samples of Arctic charr, Salvelinus alpinus (L.), were collected from the eight Cumbrian lakes containing all the known English populations. Comparative material was obtained from North Wales and southern Scotland. Comparisons were performed using otolith ages, meristic and morphological characters and by assessing allele frequencies for serum esterase and for skeletal muscle malate dehydrogenase. The results confirm that both basins of Windermere contain spring and autumn spawning races of charr. As well as differing genetically and exhibiting differing growth rates, the two races have different mean gill raker numbers and mean gill raker lengths. The latter two variables were used to derive a discriminant function which enables individual charr to be ascribed to the correct race with 94-96% accuracy. Within both principal races there were further significant differences between charr from the north and south basins of the lake and possibly also between different spawning grounds within each basin. Variation between six of the remaining seven Cumbrian populations is significant but generally no greater than that between the Windermere spring and autumn spawners. The exception is the Ennerdale charr which stands out on morphological, meristic and genetic characters, has a rapid growth rate despite its oligotrophic environment, and is a river rather than a lake spawner. The charr from North Wales and southern Scotland were clearly distinct, both from each other and from the English populations.