Arachidonic Acid Activates Cation Channels in Bovine Adrenal Chromaffin Cells

Abstract— Microscopic fluorescence analysis of fura-2-loaded bovine adrenal chromaffin cells demonstrates that ～70% of the cells responded to arachidonic acid in increasing the intracellular Ca²⁺ concentration. Because this increase was markedly less in the absence of external Ca²⁺, we examined the effect of arachidonic acid on Ca²⁺ influx electrophysiologically. Bath application of 10 μM arachidonic acid induced a long-lasting inward current when the cell was clamped at -50 mV. Other fatty acids, such as oleic acid, linoleic acid, eicosatrienoic acid, and eicosa-pentaenoic acid, were all ineffective. The current-voltage relationships suggest that arachidonic acid may activate voltage-insensitive channels. Arachidonic acid (2μM) activated a single-channel current in the inside-out patch, even in the presence of inhibitors of cyclooxygenase and lipoxygenase, possibly suggesting that arachidonic acid could activate channels directly. The onset delay of the inward channel current in the outside-out patch configuration (54.02 ± 63.5 s; mean SD) was significantly shorter than that in the inside-out patch one (197.3 ± 177.7 s). Washout of arachidonic acid decreased the probability of channel openings in the outside-out patch but not in the inside-out one. These results suggest that arachidonic acid activates channels reversibly from outside of the plasma membrane. The unitary conductarce for Ca²⁺ of arachidonic acid-activated channel was ～17 pS. The arachidonic acid-activated channel was permeable to Ba²⁺, Ca²⁺, and Na⁺ but not to Cl^?. The opening probability of the arachidonic acid-activated channel did not depend on membrane potential. These results demonstrate that arachidonic acid activates cation-selective, Ca²⁺-permeable channels in bovine adrenal chromaffin cells.     

Effects of longitudinal laparotomy on respiratory system, lung, and chest wall mechanics.

In six sedated, anesthetized, paralyzed, and mechanically ventilated guinea pigs, total respiratory system (RT,rs), lung, and chest wall resistances and respiratory system (Est,rs), lung, and chest wall (Est,w) elastances were determined before and after longitudinal laparotomy. Furthermore the resistances were also split into their initial and difference components, with the former reflecting the Newtonian resistances and the latter representing the viscoelastic/inhomogeneous pressure dissipations in the system. For such purpose the end-inflation occlusion during constant inspiratory flow method was used. During laparotomy, a statistically significant increase in respiratory system difference resistance (from 0.086 to 0.101 cmH2O.ml-1.s) significantly augmented RT,rs (from 0.157 to 0.167 cmH2O.ml-1.s). The former was entirely secondary to a significant increase in chest wall difference resistance (0.019 to 0.034 cmH2O.ml-1.s), which naturally raised chest wall total resistance (from 0.030 to 0.047 cmH2O.ml-1.s). Est,rs and Est,w also increased (14.7 and 13.1%, respectively) after abdominal incision. It can be concluded that the midline xiphipubic laparotomy accompanied by the bilateral ventrodorsal infracostal incision increases RT,rs as a consequence of augmented chest wall difference resistance and Est,rs as a result of higher Est,w.     

Developmental and regional alteration of methionine enkephalin-like immunoreactivity in seizure-susceptible E1 mouse brain

Methionine enkephalin-like immunoreactivity (ME-LI) in the brain of El mice (seizure-susceptible strain) was measured by radioimmunoassay (RIA) to elucidate the relation between seizures and the opioid system. The lyophilized supernatants of tissue extracts were subjected to ME RIA. The concentration of ME-LI in 25-day-old El mice that had no seizures was significantly decreased in the hippocampus. At the age of 50 days when El mice displayed abortive seizures, the levels of ME-LI in both El(+) and nonstimulated El(o) mice were also significantly reduced in the hippocampus and septal area. It was further shown that the ME-LI concentrations in both 150-day-old adult El(+) during interictal periods and El(o) mice were markedly decreased in the cerebral cortex, septal area, and striatum, as compared with the corresponding regions in ddY mice (seizurenonsusceptible strain; the mother strain of El). The decrease of ME-LI in the El mouse brain was generally compatible with our previous findings concerning the up-regulation of opioid delta receptors in this species. These results suggest that the reduction of ME-LI in the El mouse brain is not due to convulsions, but could be associated with the pathogenesis of seizure diathesis and seizure manifestations in the El mouse.     

Fluorescence Induction in Chloroplasts Isolated from the Green Alga, Bryopsis maxima IV. The I-D Dip

Fluorescence induction of intact Bryopsis chloroplasts whichpreviously had been illuminated in the presence of dithionitethen kept in the dark prior to measurement showed marked quenchingfrom an intermediary peak I to a lower level D before a secondaryrise to a peak P. A small hump (H), related to the membranepotential formed across the thylakoid membranes, overlappedD. The maximum extent of quenching—the I-D dip—wasattained in chloroplasts which had been illuminated for 1 secprior to dark incubation for 1 min. This illumination causedthe complete reduction of secondary electron acceptors and thepartial reduction of Q, the primary electron acceptor of photosystemII. Chloroplasts developed the capacity for transient photooxidationof cytochrome f during subsequent dark incubation, indicatingthat there was dark oxidation of electron acceptors of photosystemI which had been reduced by the illumination. A close correlationwas found between the I-D dip and the transient photooxidationof cytochrome f with respect to the kinetics of light inducedchanges as well as dark restoration after the illumination.Inhibitor studies showed that the dip decreased when the poolsize of photosystem I acceptors was reduced. Our results showthat the I-D dip and the transient photooxidation of cytochromef depend upon a common acceptor pool of photosystem I. We concludedthat the I-D dip is due to the oxidation of Q by photosystemI with a limited electron acceptor pool. (Received September 12, 1980; Accepted November 14, 1980)     

A photoactive Photosystem-II reaction-center complex lacking a chlorophyll-binding 40 kilodalton subunit from the thermophilic cyanobacterium Synechococcus sp.

The Photosystem-II reaction-center complex of the thermophilic cyanobacterium Synechococcus sp. was resolved into two complemental chlorophyll-protein complexes, CP2b which contained a chlorophyll-binding 47 kDa polypeptide, two polypeptides in the 28–31 kDa region and a 9 kDa polypeptide, and CP2c which had only a chlorophyll-binding 40 kDa polypeptide. CP2b was found to be highly active in photoreduction of 2,6-dichlorophenolindophenol with diphenylcarbazide as an electron donor. The activity was insensitive to 3-(3,4-dichlorophenyl)-1,1-dimethylurea and ioxynil but was half inactivated by the treatment of the complex at 50°C for 5 min, or on addition of 0.001% sodium dodecyl sulfate, indicating its dependence on the protein conformation. CP2c also showed a low activity of the dye photoreduction, which was insensitive to heat and enhanced at high concentrations of sodium dodecyl sulfate. The quantum yield of the photoreduction was estimated to be 0.12 for CP2b and 0.002 for CP2c. It is concluded that the 47 kDa polypeptide is the site of the Photosystem-II reaction center and the 40 kDa polypeptide is not required for the Photosystem-II-driven electron transport.