Model for the regulation of platelet volume and responsiveness by the trans-membrane Na+/K+-pump

✍ Scribed by Gerard Marx; Avigdor Blankenfeld; Rivka Panet; Raphael Gorodetsky

• Publisher: John Wiley and Sons
• Year: 1992
• Tongue: English
• Weight: 566 KB
• Volume: 151
• Category: Article
• ISSN: 0021-9541
• DOI: 10.1002/jcp.1041510205

✦ Synopsis

Services, Tel Hashomer 5262 7 (A B I, and Department of Nuclear Medicine i R P ) and 5harett Institute of Oncology (R C j , Hadasah Un/vcrsity Hosptal, lerusalcm 9 1 120, h a d

The correspondence between K + uptake in platelets to their responsiveness was studied using "'Rb+ as an analogue of K+. An average 86Rbi uptake rate of 0.73 ( I 0.140) X l o -' " mole Rb'irnin-plt (n = 20) was observed. By the use of K+-influx inhibitors, we were able to distinguish three distinct 8"Rb ' uptake pathways: an ouabain-sensitive (61 YO & 2% inhibitable) pump and two equivalent channels, only one of which is sensitive to furosemide. Other platelet parameters were also examined in conjunction with K+-uptake. Platelets incubated with ouabain exhibited an overall rise in their cell volume (MPV) with incubation time (AMPV = 7.4 x lo-" I./niin-'plt-').

Concomitantly, over 24 hours, a steady decrease in platelet number was recorded by blood cell coulter, which correlated inversely with the counts of particles, which by their size resemble white blood cells (r = 0.89). On a cellular level, incubation with ouabain induced greater expression of surface fibrinogen-receptor (GPllb), increased binding of FITC-labelled fibrinogen, and increased responsiveness to ADP. Our observations suggest the following sequence of events: Ouabain turns off the Na+iK+-ATPasc pump, which leads to water accumulation in platelets and concomitant increased MPV. Greater expression of fibrinogen receptors on the distended platelet surface corresponds to spontaneous rnicroaggregate furmation as well as greater responsiveness to agonists. Our model links volume regulation, the expression of fibrinogen receptors, and the sensitivity of platelets to agonists to the activity of the Na+/K+-ATPase pump.

1992 Wiley-Liss, Inc.