MadSci Network: Cell Biology

Re: how many mitochondria does an average human muscle contain?

Date: Fri Oct 17 00:09:27 2003
Posted By: Sanjida Rangwala, Graduate Student, Washington University
Area of science: Cell Biology
ID: 1062792625.Cb

Hello Christine,

I wasn't able to find your answer but I asked around, and a fellow moderator, 
Steve Mack, who worked on mitochondrial DNA evolution in his thesis, gave me 
this response:

See this reference paper.

Robin, E. D. and Wong, R. (1988) Mitochondrial DNA molecules and virtual number 
of mitochondria per cell in mammalian cells. J. Cell. Physiol. 136, 507-513. 

Steve says:

This paper estimated the number of "virtual" mitochondria (see below) in cells
from 5 different cell lines, which were derived from rat (skeletal muscle), 
mouse (fibroblast), rabbit (2 types of macrophage), and human (fibroblast). 
They found that the rat skeletal muscle cells had on average 140 "virtual"
mitochondria. The overall counts ranged from ~90 mitochondria per cell in
one type of rabbit macrophage to ~700 in the other type of macrophage. 

The authors used the term "virtual" mitochondria, because it was not clear if
the mitochondria existed in the cell as discrete units, or if they were part of a 
single large branching network. Today, it looks like a more accurate answer 
to this question might be something like "just one big one," because while 
individual mitochondria can exist as discrete organelles, they can just as easily 
form a giant branched "reticulum" structure. The paper from 2002 that I list 
below suggests that complete mixing of the contents of the mitochondrial 
matrices in a human cell can occur in 12 hours, and the paper from 1994 
suggests that "the actual number of mitochondria per cell is not of crucial 
importance, and mitochondria in a cell should be considered as a virtually 
single dynamic unit." 

The mass of mitochondria in a cell changes in response to the energy demands of 
the cell, but it looks like measures of mitochondrial mass are relative to the 
cell types being studied, so it is hard to say what the absoloute mitochondrial 
mass of a muscle cell is in comparison to any other cell type. However, it should
be noted that the muscle cells in a cell line are not "active" in the sense that a
working muscle is, so the count of 140 "virtual" mitochondria from the cell line
data could be a significant undercount in comparison to muscle tissue.

Here are some references for the "one big happy mitochondrion" concept : 

Frédéric Legros, Anne Lombès, Paule Frachon, and Manuel Rojo (2002) 
Mitochondrial Fusion in Human Cells Is Efficient, Requires the Inner Membrane 
Potential, and Is Mediated by Mitofusins. Mol Biol Cell. December; 13 (12): 

Hayashi J, Takemitsu M, Goto Y, Nonaka I (1994) Human mitochondria and 
mitochondrial genome function as a single dynamic cellular unit. J Cell Biol. 

Kirkwood, S.P., Munn, E.A., and Brooks, G.A. (1986). Mitochondrial 
reticulum in limb skeletal muscle. Am. J. Physiol. 251, C395–C402. 

Stevens, B. (1981). Mitochondrial structure. In The Molecular Biology 
of the Yeast Saccharomyces: Life Cycle and Inheritance, J.N. Strathern, 
E.W. Jones, and J.R. Broach, eds. (Cold Spring Harbor, NY: 
Cold Spring Harbor Press), pp. 471–504.

These references might be a bit too academic for your purposes, but I hope you 
get the general idea and that this helps,


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