Perceived barriers and biases in the medical education experience by gender and race.

This study examined barriers and biases in the medical education experience by surveying fourth-year medical students. There were 270 female and 288 male respondents; their racial background was: 21% Asian, 13% underrepresented minorities, and 66% white. Women reported that the careers they were encouraged to pursue were affected by their gender (44% versus 15%) and they were often mistaken for a nonphysician (92% versus 3%). More importantly, women reported that the lack of a mentor of either gender as a large barrier (27% versus 19%). Underrepresented minorities reported that their race caused them to feel that they had to be twice as good to be treated as an equal to other students (52% versus 6%). Underrepresented minorities identified the lack of a same-race mentor (23% versus 4%) and role model (40% versus 1%) as a large barrier. Underrepresented minorities also noted an overall lack of mentors as a large barrier (25% versus 19%). Women and underrepresented minorities from the class of 1996 reported having a medical school experience characterized by similar barriers to their professional development.

Hypoxia-induced intracellular acidification in isolated sheep heart Purkinje fibres and the effects of temperature.

The changes of intracellular pH (pHi) produced by hypoxia in sheep heart Purkinje fibres were studied using liquid ion exchanger-filled microelectrodes. A decrease of temperature from 35 degrees C to 22 degrees C caused an alkalinization of 0.3 pH units. Hypoxia (partial pressure of oxygen < 10 mm Hg) for 20 min induced an acidification of 0.26 +/- 0.18 units (n = 14) at 35 degrees C. The hypoxia-induced acidification at 22 degrees C was smaller than that at 35 degrees C by approximately 65%. Increasing the buffering capacity of the cells decreased the hypoxic acidification. This could be achieved either by use of high extracellular HEPES concentrations (40 mM) or by the use of bicarbonate buffers. Sodium cinnamate (5 mM) increased the hypoxic acidification and slowed the pHi recovery on reintroduction of oxygen, implying an importance role for lactate flux in pH regulation during hypoxia.

Intracellular pH changes induced by hypoxia and anoxia in isolated sheep heart Purkinje fibres.

The effects were studied of hypoxia on intracellular ion activities in sheep heart Purkinje fibres. The intracellular pH (pHi), surface pH (pHs), intracellular potassium activity (aki), and intracellular sodium activity (aNai) of the cells were recorded using liquid ion exchanger-filled microelectrodes. Various methods of inhibiting oxidative phosphorylation were compared for their effect on pHi. These methods were the use of hypoxia, anoxia or NaCN (2 mM). Hypoxia was produced by degassing solutions under reduced pressure then bubbling with 100% nitrogen gas. Anoxia was produced in a similar manner but with the addition of the reducing agent sodium dithionite (0.5 mM) to remove all traces of oxygen from the solutions. Anoxia caused the most marked changes. Concentration of sodium dithionite between 0.1 and 1 mM produced similar maximum rates of acidification. High concentrations (5 or 20 mM) could produce larger intracellular acidifications apparently unrelated to anoxia. The effects of hypoxia and NaCN were similar. Inhibition of Na(+)-H+ exchange with amiloride (1 mM) had little effect on the pH changes produced by hypoxia. Periods of hypoxia exceeding 1 h still resulted in rapid, readily reversible changes in pHi. Hypoxia caused a rise in aNai, the effect being larger in anoxic conditions. The intracellular K+ activity decreased in hypoxia with further decreases in anoxic conditions. The intracellular ion changes produced during hypoxia are discussed in terms of the production of lactic acid by the cells and changes in the ATP supply to the Na(+)-K+ pump.

Effects of saponin on contractile force and intracellular ion activities of cardiac tissues.

The effects of the glycoside saponin on ferret ventricular muscle have been investigated. Saponin produced a positive inotropic effect, the extent of which was determined by the bathing calcium concentration. If the bathing calcium concentration is reduced to levels equivalent to those found intracellularly then similar saponin concentrations are able to "skin" the cardiac cells. The effects were further investigated in sheep heart Purkinje fibres. In the presence of normal extracellular calcium concentrations (to prevent skinning), saponin produced increases in sodium activity, decreases in potassium activity but little change in intracellular pH. The decreases of potassium activity were compared to the effects of strophanthidin. The changes in intracellular ion levels were accompanied by the development of a contracture. The effects of saponin could be explained by its interaction with cholesterol in the cell membrane resulting in an increase in membrane permeability to sodium which may be part of a nonspecific increase in membrane permeability.