The ability of cyclic AMP to inhibit Na+, K+-ATPase activity in adrenal medulla was examined to elucidate mechanisms of cyclic AMP stimulatory modulations in catecholamine (CA) secretion from adrenal gland. Cyclic AMP...
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The ability of cyclic AMP to inhibit Na+, K+-ATPase activity in adrenal medulla was examined to elucidate mechanisms of cyclic AMP stimulatory modulations in catecholamine (CA) secretion from adrenal gland. Cyclic AMP, 10(-7) -10(-4) M, was demonstrated to inhibit Na+, K+-ATPase activity of microsomes from bovine adrenal medulla. 8-Br cyclic AMP and forskolin reduced [gamma-P-32]ATP hydrolysis by digitonin-permeabilized chromaffin cells and this reduction of ATP hydrolysis was due to an inhibition of Na+, K+-ATPase. Catalytic subunit of cyclic AMP-dependent protein kinase also reduced [gamma-P-32]ATP hydrolysis and the inhibitor of the protein kinase blocked the catalytic subunit-induced reduction of ATP hydrolysis. 8-Br cyclic AMP and forskolin inhibited Rb-86 uptake into cultured chromaffin cells. From these results, the ability of cyclic AMP to inhibit adrenomedullary Na+, K+-ATPase was shown in crude membrane fraction, in leaky cell preparation and also in intact cells.
The production of NOx by lightning over the contiguous United States has been evaluated by using combined ground-based and satellite lightning measurements. The lightning data from the National Lightning Detection Net...
The production of NOx by lightning over the contiguous United States has been evaluated by using combined ground-based and satellite lightning measurements. The lightning data from the National Lightning Detection Network (NLDN) over the period of 1995-1999, along with a ratio of intracloud (IC) to cloud-to-ground (CG) flashes derived in conjunction with satellite lightning measurements from the Optical Transient Detector (OTD), are analyzed to obtain the number of CG and IC flashes. The average annual lightning counts over the 5-year period are about 23 million for CG flashes and 55 million for IC flashes. The resulting lightning distributions are employed to calculate the production of NOx assuming a NO production rate of 6.7 x 10(26) molecules for each CG flash and 6.7 x 10(21) molecules for each IC flash. NOx production by lightning varies seasonally in accordance with the lightning distribution, with the maximum production occurring in the summer (June, July, and August) and in the Southeast. CG flashes produce more NOx than IC flashes despite fewer CG flashes by a factor of 2 or more. The geographical and seasonal production of NOx by lightning is compared to NOx emissions from other sources (i.e., from anthropogenic, soil, and biomass-burning emissions). The results indicate that regional emissions of NOx by lightning can be significant in the summertime and may play a critical role in ozone formation in the free troposphere. Our estimate of NOx emission by lightning over the United States would decrease by an order of magnitude if we use the production rates from a recent laboratory study [Wang et al., 1998] that are significantly lower than previous estimates.
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