Differential effects of cooling in hibernator and nonhibernator cells: Na permeation.

Unidirectional Na influx is less inhibited by cooling in guinea pig red blood cells than in ground squirrel cells. To isolate the source of this difference, component pathways of 24Na entry were estimated by use of selective inhibitors (ouabain, bumetanide, amiloride). Amiloride slightly inhibited influx in ground squirrel cells at every temperature between 37 and 5 degrees C. Amiloride did not consistently inhibit Na influx at 37 degrees C in guinea pig cells but caused a 44% inhibition at 25 degrees C and a 35% inhibition at 5 degrees C. Cytoplasmic acidification caused an increase in amiloride-sensitive influx in guinea pig cells, which was greater at 20 degrees C than at 37 degrees C; cytoplasmic acidification decreased amiloride-sensitive Na influx in ground squirrel cells at 37 degrees C and had no effect at 20 degrees C.