Effects of temperature on ionic transport in aortas from rat and ground squirrel

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].