Maintenance of ion concentration gradients in the cold in aorta from rat and ground squirrel

Cell water and ionic content were measured in aortic smooth muscle from rats and ground squirrels during 48 h of incubation in oxygenated Krebs solution held at low temperatures. Cells from the ground squirrel, a hibernator, maintained sodium and potassium contents near normal levels during incubation at 7°C. In sharp contrast, cells from the rat lost potassium and gained sodium with half times of 14 and 11 h, respectively. The [K] in cell water for the rat decreased 138 mM while [Na] in cell water increased about 148 mM. Cells from the hibernator tended to lose 10 mM K and gain 13 mM Na. Vascular smooth muscle of both the rat and squirrel was able to maintain K content at 17°C. Tissue content of the divalent cations Ca and Mg did not change in vessels from either animal. The present findings suggest that aortic smooth muscle cells from a hibernator have adapted in such a way as to maintain ionic gradients upon prolonged exposure to low temperatures.