Photoreceptor Spike Responses in the Hardshell Clam, Mercenaria mercenaria

Spikes were recorded from single axons in the siphonal nerve of the hardshell clam Mercenaria mercenaria which respond to dimming of light. No axons were found to respond to the onset, or increase, of illumination. In a dark-adapted state there is little or no ongoing spike activity. The responsive area of a single axon is a circle of approximately 85 µm diameter on the inner siphon wall. The number of spikes elicited at the off of constant-duration flashes grows as approximately the 0.4 power of flash intensity. For constant intensity and constant light-time fraction, the off-response increases with increasing duration at least up to 500 s duration. For long durations, the response grows as the logarithm of stimulus duration. Subthreshold light can suppress the off-response from preceding illumination. In a light-adapted state, the off-response is greater and its latency shorter than in the dark-adapted state. The fine structure of groups of cell processes thought to comprise the photoreceptor in Mercenaria is described. On the basis of morphological and physiological findings it is suggested that phototransduction occurs in the fine distal processes of the axons from which we have recorded. Axonal processes were found to contain well organized pentalaminar whorls which may be the site of photo-pigment concentration. The action spectrum obtained from the integrated responses of nerve bundles appears to be that of a single Dartnall pigment having maximal absorption at about 510 nm.     

The effects of drought stress on respiration of isolated corn mitochondria

Mitochondria were isolated from etiolated corn shoots (Zea mays L.) that were stressed to a measured water potential. The rates of mitochondrial respiration in state III, state IV, and without phosphate or ADP on a milligram protein basis decreased as water stress increased with succinate, malatepyruvate, or reduced nicotinamide adenine dinucleotide as substrates. Coupling (as determined by respiratory control and ADP/O ratios) did not decrease with increasing water stress. At water potentials greater than −35 bars all respiration had ceased.     

Trichinella spiralis: differences between "early" and "late" rapid expulsion evident from inhibition studies using cortisone and irradiation

Cortisone administered once at 100 mg/kg during the first 3 weeks of infection inhibited rapid expulsion. In rats immunized with an abbreviated infection (T/M regime) inhibition averaged approximately 50%, whereas in rats given a complete infection (C.I.) 14% inhibition occurred. Sensitivity to 400 rad whole-body irradiation was greatest 7 days before a challenge infection in all immune rats. Three days after beginning the T/M infection rats were highly susceptible to cortisone but only weakly so to irradiation. Rats immunized by C.I. were equally, but only weakly, susceptible to either cortisone or irradiation 3 days after infection. Acute administration of cortisone 1 or 4 hr prior to challenge did not inhibit rapid expulsion but 60% inhibition occurred when cortisone was given 24 hr prior to challenge. Inhibition of rapid expulsion by irradiation 7 days prior to challenge was not reversed by immune serum and irradiation did not affect antibody titer in treated rats. It was suggested that irradiation 7 days before challenge compromised the intestinal, and not the immunological, component of rapid expulsion. Differences in sensitivity of "early" and "late" rapid expulsion to irradiation and cortisone therapy provide further evidence of functional differences between these rejection processes.     

Identification of erythro-beta-hydroxyasparagine in the EGF-like domain of human C1r

Previous studies [(1987) Biochem. J. 241, 711-720] have shown that position 150 of human C1r is occupied by a modified amino acid that, after acid hydrolysis, yields erythro-beta-hydroxyaspartic acid. In view of further investigations on the nature of this residue, peptide CN1a T8/T9 TL8 (positions 147-155) was isolated from C1r A chain by CNBr cleavage followed by enzymatic cleavages by trypsin and thermolysin. Amino acid analysis, sequential Edman degradation and FAB-MS of this peptide indicate that the residue at position 150 is an erythro-beta-hydroxyasparagine resulting from post-translational hydroxylation of asparagine.     

Sphingosine inhibition of protein kinase C activity and of phorbol dibutyrate binding in vitro and in human platelets

Sphingosine inhibited protein kinase C activity and phorbol dibutyrate binding. When the mechanism of inhibition of activity and phorbol dibutyrate binding was investigated in vitro using Triton X-100 mixed micellar methods, sphingosine inhibition was subject to surface dilution; 50% inhibition occurred when sphingosine was equimolar with sn-1,2-dioleoylglycerol (diC18:1) or 40% of the phosphatidylserine (PS) present. Sphingosine inhibition was modulated by Ca2+ and by the mole percent of diC18:1 and PS present. Sphingosine was a competitive inhibitor with respect to diC18:1, phorbol dibutyrate, and Ca2+. Increasing levels of PS markedly reduced inhibition by sphingosine. Since protein kinase C activity shows a cooperative dependence on PS, the kinetic analysis of competitive inhibition was only suggestive. Sphingosine inhibited phorbol dibutyrate binding to protein kinase C but did not cause protein kinase C to dissociate from the mixed micelle surface. Sphingosine addition to human platelets blocked thrombin and sn-1,2-dioctanoylglycerol-dependent phosphorylation of the 40-kDa (47 kDa) dalton protein. Moreover, sphingosine was subject to surface dilution in platelets. The mechanism of sphingosine inhibition is discussed in relation to a previously proposed model of protein kinase C activation. The possible physiological role of sphingosine as a negative effector of protein kinase C is suggested and a plausible cycle for its generation is presented. The potential physiological significance of sphingosine inhibition of protein kinase C is further established in accompanying papers on HL-60 cells (Merrill, A. H., Jr., Sereni, A. M., Stevens, V. L., Hannun, Y. A., Bell, R. M., Kinkade, J. M., Jr. (1986) J. Biol. Chem. 261, 12010-12615) and human neutrophils (Wilson, E., Olcott, M. C., Bell, R. M., Merrill, A. H., Jr., and Lambeth, J. D. (1986) J. Biol. Chem. 261, 12616-12623). These results also suggest that sphingosine will be a useful inhibitor for investigating the function of protein kinase C in vitro and in living cells.     

sn-1,2-Diacylglycerol kinase of Escherichia coli. Structural and kinetic analysis of the lipid cofactor dependence

The lipid cofactor requirement of Escherichia coli sn-1,2-diacylglycerol kinase was studied using a beta-octylglucoside mixed micellar assay (Walsh, J. P., and Bell, R. M. (1986) J. Biol. Chem. 261, 6239-6247). The enzyme was shown to have an absolute requirement for a lipid activator. sn-1,2-Dioleoylglycerol was both an activator and a substrate for the enzyme, 1,3-dioleoylglycerol was an activator but not a substrate, and sn-1,2-dioctanoylglycerol was a substrate but not an activator. Activation was observed with a large number of phospholipids, sulfolipids, neutral lipids, and detergents. Lipids with longer alkyl/acyl chains stimulated activity to a greater extent and at lower concentrations than their shorter chain homologs. Anionic lipids were the best activators, and neutral lipids were somewhat less effective. Cationic lipids were poor activators. Lipid activation was cooperative in all cases, with Hill coefficients ranging from 2.9 to 4.7. Lipid activators stabilized the enzyme against inactivation induced by diacylglycerols. The effectiveness of several lipids in stabilizing the enzyme correlated with their effectiveness as kinetic activators, suggesting a common mechanism. Kinetic analyses also suggested that a lipid cofactor-induced conformational change occurs as a part of the activation process. beta-Octylglucoside was shown not to function as a lipid cofactor for diacylglycerol kinase. The requirement for detergent in the assay was related, instead, to the need to disperse and deliver water-insoluble substrates and cofactors to the enzyme. beta-Octylglucoside also provided an inert matrix to which lipid substrates and cofactors could be added, enabling study of their concentration dependencies.     

Neuronal and Nonneuronal Contributions to Renal Catecholamine Content in the Dog

Endogenous noradrenaline and 3,4-dihydroxyphenylethylamine (dopamine) levels were measured in different zones of the dog kidney following chronic unilateral renal denervation. In outer and inner renal cortex, and in outer medulla, greater than 95% of the tissue content of both catecholamines was contributed by renal nerves, whereas in inner medulla only nonneuronal catecholamines were found. The amounts of neuronal dopamine present in outer renal cortex were greater than would be expected for a population of solely noradrenergic nerves.     

Effect of 9.6-GHz pulsed microwaves on the orb web spinning ability of the cross spider (Araneus diadematus)

Eight cross spiders (Araneus diadematus) were exposed overnight (16 h) during web-building activity to pulsed 9.6-GHz microwaves at average power densities of 10, 1, and 0.1 mW/cm2 (estimated SARs 40, 4, and 0.4 mW/g). Under these conditions, 9.6-GHz pulsed microwaves did not affect the web-spinning ability of the cross spider.     

Abelson transformed fibroblasts lacking the EGF receptor are not tumourigenic in nude mice.

Cells transformed by the v-abl-oncogene produce large amounts of the tumour growth factor alpha TGF. alpha TGF is homologous to the epidermal growth factor (EGF) and stimulates cell growth via the EGF receptor pathway. To separate metabolic events in the v-abl-transformed cells mediated by alpha TGF as opposed to the v-abl-encoded protein-tyrosine kinase, we have employed the Swiss 3T3 variant cell line NR6 which lacks a functional EGF receptor. v-abl was found to transform efficiently NR6 cells in vitro. These transformed NR6 cells displayed a variety of in vitro properties which were indistinguishable from transformed wild-type fibroblast lines. However, in contrast to the wild-type lines, v-abl-transformed NR6 cells failed to form tumours when injected into athymic nude mice. These results imply an important function for alpha TGF and the EGF receptor in the establishment of the v-abl-induced fibrosarcomas.