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Biomedical subjects

D C Marcus

Publications and source records attributed to D C Marcus.

61 records · Page 4Linked to original sources
PubMed1978

Respiratory quotient of stria vascularis of guinea pig in vitro.

The respiratory quotient of the stria vascularis was measured in vitro by means of Cartesian diver microgasometry. A value of about 1.2 was found when the incubation medium was phosphate-buffered serum substitute with glucose as the sole substrate. This value suggests that endogenous lipids and amino acids do not contribute significantly to strial respiratory metabolism and that carbohydrate is the primary fuel in vitro. A high activity of the hexose monophosphate pathway may be responsible for raising the respiroatyr quotient above unity.

Animals↗
PubMed1978

Respiratory rate and ATP content of stria vascularis of guinea pig in vitro.

Stria vascularis from guinea pig cochleae was incubated in vitro to determine its metabolic response to variations in substrate and ion composition of the incubation medium. The respiratory rate at 37 degrees C in a medium containing glucose and pyruvate as substrate was 17.3 +/- 1.33 (SEM, n = 51) microliter O2/mg dry weight-hour. The stria could not maintain constant respiration by relying solely upon endogenous fuel stores. With substrate supplied, the ATP level could be maintained at about 73% of that existing in vivo. Glucose appears to be an adequate substrate for stria in vitro since glutamate, pyruvate, and fumarate did not increase the respiratory rate. Succinate increased respiration markedly but did not increase the ATP level. Ouabain (10(-4) M) caused a 48% decrease in the respiratory rate. Incubation in Na+-free and K"-free medium, each resulted in irreversible decrease of respiratory rate comparable to (or greater than) that caused by ouabain. These data are in accord with the high activity of Na+-K+-ATPase in the stria and the pronounced sensitivity of the endolymphatic potential to ouabain.

Adenosine Triphosphate↗
PubMedDate not supplied

Transepithelial cation movements in gerbil utricles.

The inner ear epithelium secretes potassium (K+) and absorbs sodium (Na+). The authors' experiments utilized, for the first time, isolation of the nonsensory from the sensory regions of the utricle in the vestibular labyrinth of the gerbil by means of injecting insulating seals. It was found that the isolated nonsensory region accumulated rubidium (Rb+) (as a marker for K+) in the endolymph to a level of eight times (41 mmol/l) that in the incubation medium (5 mmol/l) over a 90-minute period. However, Na+ rose during this period, suggesting that cells excluded from this preparation (sensory regions) may be involved in Na+ reabsorption. Further observations of the time course of changes in the luminal concentrations of cations suggested that the endpoints observed at 90 minutes represented a new steady state in which both Na+ and K+ concentrations were higher and lower, respectively, than under control conditions (by about 40 mmol/l each), but they were still each displaced from electrochemical equilibrium. This implies that the processes of Na+ absorption and/or K+ secretion may be shared in some way between the two regions. This finding is unexpected, based on previous models of endolymph production, in which ionic regulation has been assigned to nonsensory regions alone.

Animals↗