Assay of human erythrocyte sodium-dependent lithium efflux: the importance of timing of blood sampling.
The activity of the human erythrocyte sodium-lithium countertransport (SLC) is stable over long periods in individuals. However, it is becoming increasingly evident that the transport system is susceptible to modulation, both acutely and chronically, by various factors. In this study, the authors observed temporal variation in SLC over a period of 10 h (08.00-18.00 hours) in healthy volunteers. SLC Vmax was maximum (0 center dot 354 +/- 0.051 mmol L-1 cell-1 h-1; mean +/- SE) at 'mid-day' and significantly higher than in the morning (0 center dot 291 +/- 0 center dot 035 mmol L-1 cell, h; P < 0 center dot 010). Its value in the evening (0 center dot 316 +/- 0.042 mmol L-1 cell-1 h-1) was lower than at 'mid-day' (P < 0 center dot 045) but higher than in the morning (P < 0 center dot 037). These changes were not accompanied by any significant change in the affinity of the transporter for external sodium, Km. Changes in SLC Vmax did not correlate with the corresponding ones in either plasma cortisol or aldosterone. However, they correlated well with those in plasma renin activity, the correlation between mid-day and a.m. sets of values (r = 0 center dot 718; P = 0 center dot 019) being better than that between mid-day and p.m. (r = 0 center dot 688; P = 0 center dot 028). The authors conclude that changes in SLC occur during the day, and this need be taken into account in the planning and execution of studies involving determination of the activity of this transport system.
Department of Therapeutics, Trinity Centre for Health Science, St. James's Hospital, Dublin, Eire.
G I
GI
Adebayo
P
P
Gaffney
M
M
Sinnott
J
J
Feely
D000328:Adult; D017920:Antiporters / Q000378:metabolism*; D004912:Erythrocytes / Q000378:metabolism*; D006801:Humans; D006854:Hydrocortisone / Q000097:blood; D008094:Lithium / Q000378:metabolism*; D012083:Renin / Q000097:blood; D012964:Sodium / Q000378:metabolism*
D017920:Antiporters; C045885:sodium-lithium countertransporter; D008094:Lithium; D012964:Sodium; D012083:Renin; D006854:Hydrocortisone