The surface ultrastructure of the gill arches of the mullet, Mugil cephalus, was studied by scanning electron microscopy. Each gill arch supports two rows of gill filaments which extend posterolaterally, and two rows of gill rakers which extend anteromedially. Secondary lamellae (respiratory lamellae) extend from both lateral surfaces of each filament, and numerous secondary projections, either spiny or smooth, extend from the anteromedial aspect of each raker. Raker morphology varies somewhat from one gill arch to the next and from the dorsal to ventral aspects of the same gill arch. All surfaces of the gill arch except the respiratory lamellae and portions of the rakers are covered with a mosaic of ridged epithelial cells. These cells measure 3-10 pm in diameter, and possess concentrically arranged surface ridges which measure 0.1-0.15 pm in width. In contrast, the respiratory lamellae and the anteromedial surfaces of the rakers are covered with smooth surfaced epithelial cells lacking surface ridges. Numerous pores, having rounded cellular extensions projecting from their interiors, are irregularly located between the ridged epithelial cells. Pores are common on the apposing surfaces of the rows of gill filaments and a t the bases of the respiratory lamellae, but are rare or absent on other surfaces of the filament. Because the pores likely represent entrances to apical crypts of chloride cells, scanning electron microscopy may be useful in monitoring changes in the number and distribution of chloride cells in gill filaments of euryhaline fish during adaptation to various salinities. Although the gill filament epithelium has been thoroughly described in tissue sections, the surface ultrastructure of the gill arch has been mostly ignored. A detailed knowledge of the surface features of the intact gill arch could be of significant value in understanding the processes of respiration and osmotic regulation, which involve the exchange of substances a t the epithelial surface.The mullet, Mugil cephalus, is a good model for the study of osmotic regulation in euryhaline teleosts, because it is easily obtained, is relatively hardy in captivity, and readily adapts to abrupt changes in salinity. In preparation for studies of the effects of salt waterfresh water adaptation on the biochemistry and morphology of the teleost gill arch, we have conducted the present scanning electron microscopic investigation, and describe here the surface ultrastructure of the gill arch of the mullet, Mugil cephalus. AnimalsMullet (Mugil cephalus), 8-12 cm in length were captured with a cast net in Mississippi Sound near Ocean Springs, Mississippi. To insure they were in good health, the fish were maintained for a t least a week in aerated holding tanks (110-380 liters) a t the temperature and salinity a t which they were captured (usually 20-24°C and 10-14 g m salt/l) before sacrifice. Salinity was adjusted with Rila Marine salts (Rila Products, Teaneck, New Jersey) and fish were fed Master Mix Trout Chow (Central Soya and Subsidiar...
NO2 + NO3 (NOx), the stable oxidation products of NO, and cGMP are widely accepted as indices of in vivo NO production. Whether acute changes in urinary excretion of nitrite + nitrate (UNOXV) can be taken to reflect acute changes in renal and/or systemic NO production is not known. The present studies were conducted in the conscious rat to investigate the effect on acute changes in UNOxV, of maneuvers that (a) enhance NO production and (b) act as diuretics. L-arginine (L-arg) and acetylcholine (Ach) produce equivalent NO dependent falls in renal vascular resistance (RVR), but a much greater increase in UNOX V is seen with L-arg. D-arg does not stimulate NO and has no renal vasodilatory effect, but produces a large rise in UNOX V, and SNP lowers BP but not RVR and results in a reduced UNOX V. None of the diuretics employed should stimulate the NO system or lower RVR; however, the proximally acting agents, acetazolamide and D-arg increased UNOx V, while the loop diuretic furosemide had little effect. H2O diuresis (a distal event) led to a fall in UNOx V. These data suggest that NOx is reabsorbed extensively in the proximal tubule and that inhibition of proximal reabsorption leads to an increase in UNOx V. Also, our results show that the relationship between UNOx V and UcGMP V is unpredictable. Therefore, we conclude that measurements of acute changes in UNOxV and/or UcGMP V should be interpreted cautiously, since they may reflect altered tubular handling of NOx rather than the acute activity of the systemic and/or renal NO systems.
Rat pancreases were minced and treated with collagenase or collagenase supplemented with chymotrypsin to yield a mixture of ducts, islets, acinar cell clusters, blood vessels, and nerves . Histologically and ultrastructurally, the isolated tissues resembled their in situ counterparts in most respects, the major difference being the destruction of the basement membranes (basal laminae) . Ducts ranging in size from the common bile/main pancreatic duct to the intercalated ducts were identified in the digest, although interlobular ducts were most frequently observed .Acinar tissue fragments were separated from nonacinar structures either by flotation through discontinuous gradients of Ficoll or by sieving, the latter technique being the more efficient . Common bile/main ducts, interlobular ducts, and blood vessels were selected manually from the nonacinar fractions . Biochemical analyses showed that the entire nonacinar fraction, as well as isolated ducts and blood vessels, contained larger alkaline phosphatase, carbonic anhydrase, and Mg-ATPase specific activities than acinar tissue, whereas acinar tissue contained larger y-glutamyltranspeptidase and amylase activities . However, >63% of the total recovered activity of each enzyme was associated with the acinar tissue . Both the association of the majority of each of these enzyme activities with the acinar tissue and the similarity in specific activities associated with ducts and blood vessels indicate that none of the enzymes tested is a unique marker for interlobular and larger ducts of the pancreas of the rat.Pancreatic ducts comprise a simple cuboidal to columnar epithelium (12,16,21) and a layer of connective tissue . The ducts serve as a conduit for the movement of exocrine enzymes from the acinar cells to the duodenum and they also produce at least part of the secretin-stimulated bicarbonaterich pancreatic fluid secretion (9, 44) . The role of the ducts in fluid/electrolyte secretion has been supported by ultrastructural (24) and micropuncture (29, 43) studies and by studies of the relatively unimpaired fluid/electrolyte secretion in rats whose acinar cells have been destroyed (14) .Carbonic anhydrase in the dog (4), (Na+K)-ATPase in the rabbit (40, 48), and HC03-ATPase in the dog and cat (45) have been implicated in pancreatic fluid secretion by experiments in which specific inhibitors (acetazolamide, ouabain, and thiocyanate, respectively) reduced fluid secretion by the intact pancreas . Histochemical studies have demonstrated the presence in the duct epithelium J. CELL BIOLOGY C The Rockefeller University Press
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