Cultured cells from renal cortex of hibernators and nonhibernators. Regulation of cell K + at low temperature

Abstract

Cells were grown as primary monolayer cultures from kidney cortex of guinea pigs (nonhibernators), hamsters and ground squirrels (both hibernating species). When plates of cells were placed at 5 °C, cells of guinea pigs lost 37% of their K + in 2 h and those of the hibernator lost about 10%. Uptake of 42K into the cells exhibited a simple, single exponential time course at both temperatures. Unidirectional efflux of K + was equal to K + influx in all cultures at 37 °C and, within limits of error, in hibernator cells at 5 °C. Efflux was 3- to 5-fold greater than influx in guinea pig cells at 5 °C. After 2 h in the cold the ouabain-sensitive K + influx remaining (7–15% of that at 37 °C) was about the same in the cells of the 3 species. Cells from active hamsters and from hibernating ground squirrels, however, exhibited significantly greater pump activity after 45 min in the cold (19 and 14%, respectively). The stimulation of K + influx by increasing [K +] o did not show an increase in K m + at 5 °C in cells of guinea pigs and ground squirrels. Lowering [K +] c and/or raising [Na +] c by treatment in low- and high-K + media caused only slight stimulation of K + influx, except in cells of ground squirrels at 5 °C in which the stimulation was at least 11-times greater than at 37 °C or in cells of guinea pigs at either temperature. This altered kinetic response of K + transport to cytoplasmic ion stimulation with cooling accounted for about one-third of the improved regulation of K + at 5 °C in ground squirrel cells; the other two-thirds was attributable to a greater decrease in K + leak with cooling. The inhibition of active transport by cold in all 3 species was much less severe than that previously seen in any (Na + + K +)-ATPase of mammalian cells.