Isotopic efflux of sodium and potassium were measured in aortic smooth muscle from the rat and the ground squirrel, a hibernator, at temperatures between 37°C and 0°C. Turnover of 42K in cells of hibernators was significantly lower at 0°C than in the cells of rats. Q10 values of 1.5 at temperatures above 10°C for the hibernator and the rat suggest potassium moved passively out of cells. 24Na turnover in K-free solution was highly temperature dependent in all groups; Q10 between 2.6 and 3.7 imply that this passive movement of sodium was not by free diffusion. K-stimulated 24Na turnover at 8°C was significantly greater in the aortas from both normothermic and hibernating squirrels than in those from rats. Turnover followed Arrhenius' theory between 37°C and 8°C in squirrel tissues. However, in the rat vessel the Arrhenius plot demonstrated a distinct break at 17°C, at which temperature the Q10 increased more than 3-fold to 8.8. It is suggested that cells of the hibernator may have undergone alterations in lipids which maintain 'fluidity' in the domain of the transport sites during cold. A model is proposed to explain the maintenance of ionic gradients at 7°C by the hibernator. An important factor is the stimulation of active transport by a small increase in cell [Na].
ASJC Scopus subject areas
- Cell Biology