TABLE 2.

Estimated concentration of exosome-transported PGJ₂ in endosomes of target cells

	A	B	C	D	E	F
	Mean diameter	Mean volume of 106 cells or their endosomes	Exosomes internalized in 106 cells in 1 h	PGJ2 transported by 1 µg exosomes	Final PGJ2 concentrati on in cells or endosomes	Concentration ratio
		ml	µg	pmoles	µM
1) Exosomes			1	0.193
2) Cell	15 µm	1.76 × 10−3			0.11	1
3) Endosomes	600 nm
4) Total endosome compartment		3.38 × 10−6			57.1	519

The amount of PGJ2 (column D) transported by the amount of exosomes plotted in column C was converted into µM concentrations (column E) either by considering the total volume of the recipient cells (column E line 2), or the total volume of late endosomes present in cells (column E line 4). The resulting values indicated that PGJ2 was about 500 times more concentrated in the total endosome compartment than in the total cell volume (column F). Column A: Values were obtained from literature data (see “Results”) and correspond to RBL-2H3 cells. Column B: The total volume of 10⁶ cells (line 2) and the corresponding volume of their endosome compartment (line 4) were calculated from data in column A (1 ml = 10¹² µm³). Column C: Net amount of exosome internalized in 10⁶ cells in 1 h (from Fig. 4D). Column D: Amount of PGJ₂ transported by the amount of exosome in column C; calculated from data in Fig. 3E [average of 193 pmol/mg protein in exosomes (Fig. 3E, right bars)]. Column E: PGJ₂ concentrations obtained by dividing the amount of PGJ₂ (column D) by the volume of cells (column B, line 2) or the volume of their total endosome compartment, considering an average of 30 endosomes per cell (column B, line 4). Column F: Ratio between PGJ₂ concentrations in endosomal compartment versus total cell. The same calculation procedure was applied to the other prostaglandins and two typical fatty acids [arachidonic acid (AA) and docosahexaenoic acid (DHA)] from data in Fig. 3 and reported in “Results.”

^a30 endosomes per cell.