Effect of local anesthetics on plasma protein secretion by rat hepatocytes

The effects of some local anesthetics on plasma protein secretion by rat liver slices have been studied and have been compared with those of colchicine. Rat liver slices were pulse-labelled with l-[¹⁴C]leucine for 9 min at 37°C, collected on filter paper, washed with non-radioactive leucine and reincubated in the presence or absence of the drug to be tested. The radioactive plasma proteins produced were obtained by immunoprecipitation from either the chase medium or from the washed slices. Chlorpomazine, (3 · 10^?5 M), dibucaine (10^?5 M), lidocaine (10^?3 M) and procaine (5 · 10^?5 M) inhibited both the synthesis and secretion of plasma protein but did not affect the uptake of l-leucine into the slices nor the incorporation of phosphate into intracellular nucleotide phosphates or into phopholipids. The inhibition of secretion elicited by these drugs is probably not due to the inhibition of protein synthesis since cycloheximide, when added to the chase medium at a concentration which completely inhibits protein synthesis, did not inhibit plasma protein secretion, while cycloheximide plus procaine did inhibit secretion and also caused a retention of non-secreted plasma proteins within the slices. Unlike colchicine, howover, procaine did not cause the retained plasma proteins to accumulate in Goli-derived secretory vesicles, but showed a more general effect causing a distribution among several cell fractions.     

Actigraphy: A Means of Assessing Circadian Patterns in Human Activity

-Twenty-three diurnally active (0705-2333), healthy persons between 22 and 54 yrs of age and without history of sleep abnormality were monitored continuously for 120 consecutive hr (five days) by wrist actigraphy. Circadian rhythms of high amplitude were detected by cosinor analysis for each participant and for the groups of 10 males and 13 females with the average span of heightened activity timed between ∼1330 and 1605. The circadian peak-trough difference in wrist movement was marked, equalling aproximately 75% of the 24-hr mean level. In 19 of 23 participants, the 24-hr mean of wrist activity varied between 140-180 movements/min, with four persons exhibiting lesser means of 110-140 movements/min. With respect to the daytime span of activity, the mean wrist movement of individual participants ranged from 155-265 movements/min, with the majority (20/23) varying between 185-245 movements/min. During nocturnal sleep the mean wrist activity level was quite low, varying between individuals from 5 to 25 movements/min for 21 of 23 persons. Wrist actigraphy proved to be well-accepted and was a most reliable means of monitoring aspects of body movement during activity and sleep in ambulatory persons adhering to usual life habits and pursuits.     

Extended reading frame of a ubiquitin gene encodes a stable, conserved, basic protein

Antibodies specific for the 80-amino acid hypothetical protein encoded by the in-frame, 3'-extension of a human ubiquitin gene were produced in rabbits by immunization with a 14-residue synthetic peptide. When used to probe HeLa cell extracts for the non-ubiquitin product of this natural fusion gene, the antipeptide sera detected a protein with an apparent molecular weight of 16,000 Da by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. An immunoreactive protein of identical mobility was detected in organisms ranging from Acanthamoeba to man, indicating that the extension protein, like ubiquitin, is highly conserved. The immunoreactive protein was isolated from calf thymus, and direct sequencing revealed the first 16 amino acids to be identical to those predicted from the extension portion of the human cDNA. Thus, ubiquitin was no longer present at the amino terminus. The purified bovine extension protein failed to react with a ubiquitin-specific antibody indicating the absence of isopeptide-linked ubiquitin as well. Moreover, by denaturing gel permeation chromatography the extension has a molecular weight of 10,000 Da, a value that corresponds more closely to the size of the extension alone (9,000 Da) than to the intact fusion protein (17,500 Da). The extension protein, which was found in both cytoplasmic and nuclear fractions of HeLa cells, persisted at high levels when protein synthesis was blocked with cycloheximide or puromycin. These results show that the 80-residue extension protein is the stable, processed product of the ubiquitin fusion gene.     

Mechanism involved in the mobilization of neutrophil calcium by 5-hydroxyeicosatetraenoate

5-Hydroxyeicosatetraenoate (5-HETE), like leukotriene B4 and platelet-activating factor, stimulated human polymorphonuclear neutrophils to mobilize intracellular calcium. The three compounds acted through mechanisms that were inhibited by pertussis toxin, cholera toxin, and PMA. Each agonist, furthermore, desensitized (or down-regulated) the neutrophil's calcium mobilization response to a second challenge with the same agonist. However, 5-HETE and leukotriene B4 had little or no activity in cross-desensitizing neutrophil responses to each other or to platelet-activating factor. Furthermore, 5-HETE interfered minimally or not at all with the binding of radiolabeled leukotriene B4 and platelet-activating factor to their respective receptors on neutrophils. Thus, 5-HETE mobilizes neutrophil calcium by a mechanism different from those used by leukotriene B4 and platelet-activating factor. This mechanism appears to involve specific 5-HETE receptors that couple to pertussis toxin-inhibitable, GTP-binding proteins.     

Regulation of apo-A-I processing in cultured hepatocytes

Apo-A-I, the major protein component of high density lipoproteins, appears intracellularly as an intermediate precursor (pro-apo-A-I) with a hexapeptide extension (RHFWQQ) at its amino terminus. Proteolytic processing of pro-apo-A-I to apo-A-I has been shown to occur extracellularly in cell and organ cultures from rat and human tissues. Recently, however, intracellular conversion has been detected in chickens. To determine what distinguishes and regulates these two processing methods, the proteolytic processing and secretion of apo-A-I was studied by metabolic labeling in chick hepatocytes and in Hep-G2 cells (derived from a human hepatocellular carcinoma). The proportions of intracellular and secreted pro-apo-A-I and apo-A-I were measured by sequencing NH2-terminal portions of the proteins and determining the location of radio-labeled amino acids. Chick hepatocytes cultured in the absence of hormones or fetal bovine serum secreted primarily processed apo-A-I (83%). In the presence of serum these cells secreted only pro-apo-A-I, whereas incubation with a combination of hormones (insulin, triiodothyronine, dexamethasone) resulted in secretion of a nearly equal mixture of the pro- and processed forms of the protein. In contrast, Hep-G2 cells, maintained in the absence of serum, secreted only pro-apo-A-I; when grown in the presence of serum these cells secreted a mixture of pro- and processed apo-A-I. Under conditions in which chick hepatocytes and Hep-G2 cells secreted both forms of the protein, a mixture of pro- and processed apo-A-I was also found intracellularly; when only the pro-form was secreted, the cells likewise contained only pro-apo-A-I. Under all the above conditions, the secreted apo-A-I exhibited similar isoform patterns in two-dimensional gel electrophoresis. These data show that both chick hepatocytes and human hepatoma cells are capable of intracellularly processing pro-apo-A-I to apo-A-I, and that the extent of intracellular processing is controlled by the cell's hormonal environment.     

Calcium domains associated with individual channels can account for anomalous voltage relations of CA-dependent responses.

Computer-assisted modeling of calcium influx through voltage-activated membrane channels predicted that buffer-limited elevation of cytoplasmic free calcium ion concentration occurs within microscopic hemispherical "domains" centered upon the active Ca channels. With increasing depolarization, the number of activated channels, and hence the number of Ca domains, should increase; the single-channel current should, however, decrease, thereby decreasing Ca2+ accumulation in each domain relative to the macroscopic current. Such voltage dependence of the microscopic distribution of Ca2+ may influence relations between total Ca2+ entry and Ca-dependent processes. Ca-mediated inactivation of Ca channels in Aplysia neurons exhibits behavior consistent with the calcium domain hypothesis.     

Infectious hypodermal and hematopoietic necrosis,a newly recognized virus disease of penaeid shrimp

Populations of the Pacific blue shrimp, Penaeus stylirostris, reared at the University of Arizona's experimental shrimp culture facility on Oahu in Hawaii from late 1980 through 1981, were severely affected by a highly acute and lethal disease of viral etiology. Also found to be susceptible to the disease were P. vannamei and P. monodon. The disease was named infectious hypodermal and hematopoietic necrosis (IHHN) disease to describe the principal lesions observed. The histopathology of acute and subacute IHHN disease in these species was dominated by the presence of conspicuous eosinophilic intranuclear-inclusion bodies of the Cowdry type A variety in ectodermally (especially the cuticular hypodermis) and mesodermally (especially the hematopoietic tissues) derived tissues that were undergoing necrosis. Electron microscopy of affected tissues demonstrated the presence of two or three types of virus-like particles with cubic morphology and diameters of 17 to 27 nm that suggest IHHN virus to be either a parvo- or picornavirus.     

Regulation of fibrinogen assembly. Transfection of Hep G2 cells with B beta cDNA specifically enhances synthesis of the three component chains of fibrinogen

Previous studies indicated that synthesis of B beta chain may be a rate-limiting factor in the production of human fibrinogen since Hep G2 cells contain surplus pools of A alpha and gamma but not of B beta chains, and fibrinogen assembly commences by the addition of preformed A alpha and gamma chains to nascent B beta chains attached to polysomes. To test whether B beta chain synthesis is rate limiting Hep G2 cells were transfected with B beta cDNA, and its effect on fibrinogen synthesis and secretion was measured. Two sets of stable B beta cDNA-transfected Hep G2 cells were prepared, and both cell lines synthesized 3-fold more B beta chains than control cells. The B beta-transfected cells also synthesized and secreted increased amounts of fibrinogen. Transfection with B beta cDNA not only increased the synthesis of B beta chain but also increased the rate of synthesis of the other two component chains of fibrinogen and maintained surplus intracellular pools of A alpha and gamma chains. Transfection with B beta cDNA did not affect the synthesis of albumin, transferrin, or anti-chymotrypsin and had a small inhibitory effect on the synthesis of C-reactive protein. Taken together these studies demonstrate that increased B beta chain synthesis specifically causes increased production of the other two component chains of fibrinogen and that unequal and surplus amounts of A alpha and gamma chains are maintained intracellularly.