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A Power Grid in Muscle Cells Has Profound Design Implications

Photo credit: pisauikan via Unsplash.

A finding announced in Nature represents a blockbuster for intelligent design. We knew about ATP synthase — that rotary engine that uses proton flow to create “batteries” of energy-packed ATP molecules. Those motors in the mitochondria are arranged along folds (cristae) in the mitochondrial membranes to maximize their output.

But researchers have learned that the mitochondria themselves are connected by electrical wires in a vast intracellular network. This allows us to see another level in the hierarchy of design in the cell.

The findings are of revolutionary significance. Skeletal muscle cells were known to have many mitochondria, but it was not clear how the products of ATP production, called metabolites, became distributed throughout the cell. Many assumed it was by diffusion, or simple spreading out of molecules from regions of high concentration to areas of low concentration. The truth is far more exciting. Research news from the National Institutes of Health explains:

A new study overturns longstanding scientific ideas regarding how energy is distributed within muscles for powering movement. Scientists are reporting the first clear evidence that muscle cells distribute energy primarily by the rapid conduction of electrical charges through a vast, interconnected network of mitochondria — the cell’s “powerhouse” — in a way that resembles the wire grid that distributes power throughout a city. The study offers an unprecedented, detailed look at the distribution system that rapidly provides energy throughout the cell where it is needed for muscle contraction. [Emphasis added.]

Introducing the “Mitochondrial Reticulum”

Diffusion is too slow for a fast-acting muscle cell. Electricity, though, is fast. The same proton-motive force that powers ATP synthase is conducted along cellular wires, the researchers found. You’ve heard of the endoplasmic reticulum. They’re calling this one the “mitochondrial reticulum” — a conductive pathway for energy distribution. The Editor’s Summary of the paper puts it this way:

How is energy distributed within the cell? In the skeletal muscle, energy distribution has been proposed to occur through metabolite-facilitated diffusion, although genetic evidence has raised questions about the importance of this mode of distribution. Using various forms of high-resolution microscopy, Robert Balaban and colleagues explore whether the mitochondria themselves — as well as actually generating the energy — also have a role in its distribution. They find that they do, by forming a conductive pathway throughout the cell in the form of a proton-motive force. Throughout this network, the mitochondrial protein localization seems to be varied, allowing optimized generation and utilization of the mitochondrial membrane potential. This energy distribution network, which depends on conduction rather than diffusion, is potentially extremely rapid, thereby enabling muscle to respond almost instantaneously to new energy demands.

Not only is the system extremely fast, it is well organized. The Abstract states:

Within this reticulum, we find proteins associated with mitochondrial proton-motive force production preferentially in the cell periphery and proteins that use the proton-motive force for ATP production in the cell interior near contractile and transport ATPases. Furthermore, we show a rapid, coordinated depolarization of the membrane potential component of the proton-motive force throughout the cell in response to spatially controlled uncoupling of the cell interior. We propose that membrane potential conduction via the mitochondrial reticulum is the dominant pathway for skeletal muscle energy distribution.

The mitochondrial reticulum was known before, but scientists had not previously seen that it conducts electricity. The potential of this discovery to shed light on muscular dystrophy, heart disease, and other disorders is apparent.

The images in the paper even look like a power grid. More:

For the current experiments, the NIH scientists collaborated in a detailed study of the mitochondria structure, biochemical composition, and function in mouse skeletal muscle cells. The researchers used 3D electron microscopy as well as super-resolution optical imaging techniques to show that most of the mitochondria form highly connected networks in a way that resembles electrical transmission lines in a municipal power grid.

A Case of Design Prediction

It’s clear why this is a superior design to diffusion. Strenuous exercise can raise the power demands of a muscle cell by 100-fold. “Researchers have suspected that a faster, more efficient energy pathway might exist but have found little proof of its existence — until now,” we read. That’s a case of design prediction!

Robert Balaban of the National Heart, Lung, and Blood Institute (NHLBI), a co-leader of the team, tells more about how well-optimized the organization of this power grid is. 

The study provides unprecedented images of how these mitochondria are arranged in muscle. “Structurally, the mitochondria are arranged in such a way that permits the flow of potential energy in the form of the mitochondrial membrane voltage throughout the cell to power ATP production and subsequent muscle contraction, or movement,” Dr. Balaban explained. Mitochondria located on the edges of the muscle cell near blood vessels and oxygen supply are optimized for generating the mitochondrial membrane voltage, while the interconnected mitochondria deep in the muscle are optimized for using the voltage to produce ATP, Balaban added.

This implies another level in the design hierarchy: not only is the power grid well organized inside the cell, but the cells are organized in the muscle tissues for the optimum utilization of the power where it is needed most.

Implications for Intelligent Design

The implications of this spectacular discovery for intelligent design are profound. To see why, we must remember that muscles first appear in the Cambrian explosion. Many of the Cambrian phyla that burst on the scene had muscles for contraction (jellyfish), crawling (worms), fin movement (Anomalocaris and Metaspriggina, the vertebrate fish), and coordinated action of jointed appendages (trilobites and other arthropods). Most of the Cambrian animals used muscles in various ways. Muscles are but one of many new cell types that appear suddenly, fully functional, across multiple phyla in the early Cambrian.

As Stephen Meyer emphasizes in Darwin’s Doubt, these new cell types are arranged in a hierarchy: tissues, organs, systems — and ultimately, integrated body plans. This hierarchical arrangement of complex parts for unified function challenges all undirected mechanisms such as natural selection. It takes foresight — a plan for a functional goal and the means to achieve it — to bring parts together into a hierarchical arrangement that works. The film Darwin’s Dilemma illustrates this point as well. In our uniform experience, Meyer argues, the only cause capable of doing that is intelligence. 

Now we can extend this hierarchical thinking into the arrangement inside one new cell type in a Cambrian animal: a muscle cell. That optimal hierarchical arrangement, furthermore, extends downward into the intracellular environment and upward into the tissue in which the cell resides. It’s hierarchy all the way down.

This article was originally published in 2015.