Unequal distribution of ions between the interior and exterior is characteristic of living cells. In many thus far studied the concentration of potassium is much higher in the interior while the concentrations of sodium and chloride are lower. This ionic asymmetry is associated with a potential difference across the plasma membrane which is approximately related to the relative concentration of potassium (Hober, 1945; Hodgkin, 1951) according to the Nernst equation:or at 20 C., E (in mv.) = -58 log (A + )o Membrane potentials have been recorded from many cells (Hodgkin, 1951 ;Grundfest, 1955), including some whose internal potassium concentration is known, by means of a fine, saline-filled, microcapillary (Gelfan, 1927(Gelfan, , 1931Ling and Gerard. 1949) inserted through the cell surface. The magnitude of this potential in different cells ranges from 50 to 100 mv., inside negative. This indicates an internal excess of potassium approximately 9 to 50 times the external concentration, and is in approximate accord with the observed values in specific cases in which potassium concentration has been determined.
Abstract:The objective of this study was to evaluate Sargassum meal as feed for sheep through the measures of in vivo digestibility, dry matter degradability, pH, ammonia and volatile fatty acids in rumen. The Sargassum algae used in this experiment were collected at the end of spring, when they are more abundant, bigger, and have completed their reproductive cycle. Four tons (wet weigth) were collected manually from the intertidal zone of La Paz bay, Baja California Sur, Mexico. These algae were sun-dried and ground in a hammer mill to obtain the Sargassum meal. Four fistulated Pelibuey sheep, were fed daily with diets containing the marine algae (MA) at different levels (0, 10, 20 and 30 %), using a 4 x 4 Latin-square design experiment. Feed intake was not affected (p>0.05). Water consumption and urine excretion increased with MA (p<0.05; r 2 =0.54 and r 2 =0.74, respectively). In all treatments dry matter digestibility was of 74%-79%, and crude protein digestibility was of 85%-88%. Acid detergent fiber (59%-65%) and neutral detergent fiber (55%-66%) digestibility were greater in all treatments with MA. Ruminal pH was greater in all groups fed with MA (p<0.05). Ammonium concentration was not influenced (p>0.05) by MA. Ruminal volatile fatty acids decreased in all MA groups (p<0.05). The marine algae Sargassum spp. can be used as a feed supplement for sheep, especially in tropical and subtropical regions where these marine algae are available. Rev. Biol. Trop. 57 (4): 1271-1281. Epub 2009 December 01.
We have studied the differentiation of the vitelline coat (VC) of the ascidianCiona intestinalis. In the young previtellogenic oocyte the vitelline coat precursor material (VCPM) makes its first appearance as patches of fibrous material in close apposition to the outer surface of the oocyte. The presence of subcortical vescicles containing a fuzzy electron-dense material and their opening into the oocyte surface parallels the formation of VCPM. Numerous microvillar-like structures emerge from the oocyte surface. When the VCPM completely surrounds the oocyte the microvilli are withdrawn. An overall increase of VCPM parallels the growth of the oocyte. The next step in the differentiation of the vitelline coat consists in the packing of the constituent fibrils in a dense layer at its outer surface, i.e. the one in contact with the follicle cells. At this time the VC is penetrated by microvilli protruding both from the oocyte and follicle cells. The VC reaches its final structure and thickness at the time the test cells are extruded into the perivitelline space.The participation of the follicle cells in VC organization is also discussed.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.