Effects of haemoglobin O2 saturation on volume regulation in adrenergically stimulated red blood cells from the trout, Oncorhynchus mykiss.

Adrenergic stimulation of trout red blood cells activates a Na+/H(+)-exchange. If unopposed, the ensuing increase in cell Na+ leads to an isosmotic cell swelling. In this study the effect of the level of haemoglobin O2 saturation on volume regulation has been investigated in adrenergically stimulated red blood cells from trout: at full haemoglobin O2 saturation, net influx of Na+ through the Na+/H(+)-exchanger was balanced by net efflux of K+ and no increases in cell volume took place. In contrast, at low O2 saturation (8-14%) adrenergic stimulation led to a substantial increase in cell Na+, K+ and volume. Moreover, cell volume recovery after adrenergic swelling was incomplete at low O2 saturation, whereas cells at high O2 saturation exhibited a fast and complete cell volume recovery. In cells exposed to alternating high and low O2 saturation, volume regulation was similar to the regulation found in cells maintained at high O2 saturation. In cells at high O2 saturation, extrusion of cellular Na+ by the Na+/K(+)-pump significantly contributed to the volume decrease. It is concluded that trout red blood cells at high or alternating O2 saturations possess a powerful regulatory volume decrease response that is shut off at low O2 saturation. The physiological implications of this regulation is discussed.