Abstract
The rates of synthesis, turnover, and half-lives were determined for brain microsomal ether phospholipids in the awake adult unanesthetized rat. A multicompartmental kinetic model of phospholipid metabolism, based on known pathways of synthesis, was applied to data generated by a 5 min intravenous infusion of [1,1-(3)H]hexadecanol. At 2 h post-infusion, 29%, 33%, and 31% of the total labeled brain phospholipid was found in the 1-O-alkyl-2-acyl-sn-glycero-3-phosphate, ethanolamine, and choline ether phospholipid fractions, respectively. Autoradiography and membrane fractionation showed that 3% of the net incorporated radiotracer was in myelin at 2 h, compared to 97% in gray matter microsomal and synaptosomal fractions. Based on evidence that ether phospholipid synthesis occurs in the microsomal membrane fraction, we calculated the synthesis rates of plasmanylcholine, plasmanylethanolamine, plasmenylethanolamine, and plasmenylcholine equal to 1.2, 9.3, 27.6, and 21.5 nmol. g(-1). min(-1), respectively. Therefore, 8% of the total brain ether phospholipids have half-lives of about 36.5, 26.7, 23.1, and 15.1 min, respectively. Furthermore, we clearly demonstrate that there are at least two pools of ether phospholipids in the adult rat brain. One is the static myelin pool with a slow rate of tracer incorporation and the other is a dynamic pool found in gray matter. The short half-lives of microsomal ether phospholipids and the rapid transfer to synaptosomes are consistent with evidence of the marked involvement of these lipids in brain signal transduction and synaptic function.
Highlights
The rates of synthesis, turnover, and half-lives were determined for brain microsomal ether phospholipids in the awake adult unanesthetized rat
For the first time, synthesis rates, turnover times, and half-lives of brain microsomal ethanolamine and choline ether phospholipids in vivo, and show that in the adult rat the tracer is preferentially incorporated into gray matter regions
JhexPakOH ϭ JPakOHPakCho ϩ JPakOHPakEtn JPakOHPakEtn ϭ JPakEtnPlsEtn ϭ JPlsEtnPlsCho (Eq 5) (Eq 6). Both equations five and six must hold to the extent that the assumption of steady state is valid. These assumptions and the recognition that synthesis of ether phospholipids occur in the peroxisomes and microsomes by reactions outlined in Fig. 1 allows us to estimate the transfer coefficients of the tracer into the stable ether phospholipids, use these coefficients to calculate the rates at which the microsomal ether phospholipids are synthesized and turnover
Summary
[1,1-3H]hexadecanol (55 Ci иmmolϪ1 у97% pure) was purchased from Moravek Biochemicals (Brea, CA). Neutral lipids and brain HOGpl from the phospholipid separation were extracted from the silica gel using n-hexane [2-propanol (3:2, v/v) ϩ 5.5% H2O]. Samples and standards were applied to 20 cm ϫ 20 cm Analtech silica gel G TLC plates and the neutral lipids separated as previously described [45]. The radioactivity (dpm иgramϪ1) of hexadecanol and of the different ether phospholipids was measured in plasma and whole brain extracts of rats killed at 5, 10, 20, 30, 60, or 120 min following the start of infusion. Both equations five and six must hold to the extent that the assumption of steady state is valid These assumptions and the recognition that synthesis of ether phospholipids occur in the peroxisomes and microsomes (microsomal fraction) by reactions outlined in Fig. 1 allows us to estimate the transfer coefficients of the tracer into the stable ether phospholipids, use these coefficients to calculate the rates at which the microsomal ether phospholipids are synthesized and turnover
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
