A model for the stimulation of taste receptor cells by salt

A taste cell mucosal surface is regarded as a planar region containing bound anionic sites and openings to ionic channels. It is assumed that the bulk aqueous properties of the exterior phase are not continuous with the surface but terminate at a plane near the surface. The region between the (Stern) plane and the membrane is regarded as having a lower dielectric constant than bulk water. This fact admits the possibility of ion pair formation between fixed sites and mobile cations. Mobile ion pairs entering the region may also bind to a fixed anionic site. Thus, it is assumed that mobile cations and ion pairs are potential determining species at the surface. Binding cations neutralizes surface charges, whereas binding mobile ion pairs does not. This competition accounts for the observed anion effect on stimulation of tast receptors by sodium salts. The potential profile is constructed by superimposing the phase boundary potentials with an ionic diffusion potential across the membrane. The model accounts for the anion effect on receptor potential, pH effects, the reversal of polarity when cells are treated with FeCl3, and the so-called "water reponse," depolarization of the taste cell upon dilution of the stimulant solution below a critical lower limit. The proposed model does not require both bound cationic and anionic receptors, and further suggests that limited access to a Stern-like region continuous with membrane channels may generally serve to control transport of ions.     

An analysis of the need for pediatric surgeons in the United States

A questionnaire study covering all major population areas in the United States indicated that pediatric surgeons and potentially capable hospitals are already well-distributed throughout the country. The estimation of need for pediatric surgeons based on the area questionnaires is close to the present number of surgeons. A computer analysis was made to project numbers of pediatric surgeons per unit population to the year 2000 with differing levels of trainee output. The study indicates that 14-15 training programs are sufficient to allow for slow, modest growth of the specialty if current population trends continue.     

Ultrastructures of atypical acinar cell nodules in rat pancreas induced by 4-hydroxyaminoquinoline-1-oxide

A single intravenous injection of 4-hydroxyaminoquinoline-1-oxide (4HAQO) to rats induces multiple atypical acinar cell nodules in the pancreas. In this study, the ultrastructure of cells in these nodules was examined at 6, 9, and 12 months, and the features were compared to those of developing embryonal pancreas. The cells in the nodules are exocrine acinar cells in type and exhibited several features which distinguish them from the nonnodular acinar cells. Irregular nuclear shape with enlarged nucleoli was frequently observed. Zymogen granules in the nodular cells appeared as vesicles with contents of extreme electrom lucency and their ultrastructural appearance was similar to those of developing embryonic pancreatic acinar cells at 16 and 18 days of gestation. At the cell periphery, the lateral cell membrane showed bizarre interdigitation and the ectoplasm showed hyaloplasmic rarefaction. These findings indicate that the acinar cell nodules induced by 4-hydroxyaminoquinoline-1-oxide are composed of a new population of phenotypically altered acinar cells showing nuclear abnormalities, modified cell to cell interaction, and a possible defect in synthesis and/or maturation of secretory enzymes. The latter may indicate an arrest in the differentiation of acinar cells. The significance of these findings is discusses, and it is suggested that the atypical nodules in the pancreas induced by 4-hydroxyaminoquinoline-1-oxide may represent early neoplastic foci.     

Glucose and bicarbonate reabsorption in edematous dogs

Glucose and bicarbonate reabsorption were studied in dogs made edematour by aortocaval fistula (A-V dogs) and in sham-operated dogs. Following construction of the A-V fistula, there was a significant increase in body weight; glomerular filtration rate, renal plasma flow, hematocrit, and sodium excretion decreased significantly. Bicarbonate reabosorption was significantly higher in A-V than in sham dogs both during control and volume expansion. Volume expansion depressed bicarbonate reabsorption significantly in both groups. Glucose reabsorption fell following volume expansion in both groups; glucose reabsorption was significantly higher in A-V dogs than in sham dogs during control and volume expansion. Volume expansion led to a minimal increase in sodium excretion in A-V dogs when compared to the increase in the sham dogs. These data demonsttate that chronic sodium retention is associated with enhanced reabsorption of glucose and bicarbonate. The site in the neophron responsible for the increase in reabsorption of these substances cannot be determined with certainty based on these clearance studies although it is possible that proximal reabsorption may be enhanced in this model.     

Regulation of nitrogen catabolic enzymes in chick liver -- effects of amino acids

It is well-known that in the chick, dietary protein increases the levels of several hepatic enzymes that are involved in nitrogen metabolism and excretion. However, the biochemical mechanism of this response is essentially unknown. The experiments presented in this paper show that the chick is responding to alpha-amino nitrogen and not to any specific amino acid. Furthermore, it is shown that this system responds to endogenous sources of nitrogen as well as dietary protein and that the xanthine dehydrogenase response involves regulation of enzyme synthesis without changing the rate of degradation.