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Authors: Andrew Koob
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for an organism to actually be “multicellular,” requires calcium. A calcium signal tells flowers to bloom (see Figure 5.1 ).
FIGURE 5.1 Calcium in action
In the field of biology, the removal of tissue cells from animals and subsequently culturing them in a Petri dish is a common practice. Cells adhere to each other like in tissue when they are placed in a culture dish.Just as human beings are social creatures who need other human beings, so cells need other cells, a process that relies entirely on calcium. Without calcium, the cells are unable to grow as quickly and their structures change. They isolate themselves and eliminate cell interaction.
Extracellular calcium is 20,000 times higher than intracellular calcium. However, the cell has internal complexes that also store calcium at 10–50 times the rate of the surrounding intracellular space. The wide disparity of calcium concentrations inside and outside the cell is due to the interactivity of calcium when it is not controlled. Most calcium inside the cell is attached to proteins and sequestered in internal cell complexes. On the planet earth, calcium cannot exist freely without interacting with something. Like the most respected member of a family, all important matters in the cell involve calcium.
Further calcium experiments were performed on muscle after Ringer’s famous experiments. Extracellular calcium can stop muscle contraction. When it drops below a certain level, muscles twitch uncontrollably. Calcium is also stored in neurons at the synapse. When the electrical signal reaches the end of the axon, calcium floods the synapse from the extracellular space like people into a store for a 50 percent off sale. The calcium “flux” causes a release of calcium from sequestered stores inside the cell and is required for transmitter release. Because the understanding of calcium in the cell came about later than Hodgkin and Huxley’s squid giant axon experiments, the belief is that calcium contributes to the electrical gradient more than previously expected.
In astrocytes, the main signaling comes from complexes inside the cell called “internal calcium stores.” Neurons require the electrical axon impulse for calcium influx from the extracellular space to enter at the synapse and affect transmitter release. External calcium influencing transmitter release has been shown to come from astrocytes.
In the short paper published by Murphy and colleagues, which showed that transmitters can institute a calcium increase in astrocytes, they were concerned with a single cell and did not understand the extent of astrocyte reception of neuronal communication. A neuron signaling to an astrocyte could carry information from our senses. If neurons are the only cell involved in mental processing, why would astrocytes respond to the sensory stimulus of neurons? At the point of their discovery, Murphy and his colleagues did not understand that astrocytes might also be able to signal to other astrocytes and to neurons themselves.
A couple papers from Yale, the first by Ann H. Cornell-Bell and colleagues in 1990, demonstrated that calcium waves occur in astrocytes when they are stimulated. After a transmitter acts on an astrocyte or a researcher mechanically stimulates the cell with an electrode—a long plastic tip about 1/200th of a millimeter wide—the calcium wave spreads from one astrocyte to the next. The spread is similar to what Golgi described—through physical connections between the star-like cells long arms—similar to billions of octopi holding hands.
The understanding of how the cells held hands began in 1969. Researchers at the National Institutes of Health, Milton Brightman and Thomas S. Reese, laid the foundation for what would be known as the gap junction. Looking at pictures taken with the electron microscope, they demonstrated that astrocytes—with the ends of their processes probing blood vessels and neuronal surfaces—also come into contact with
FIGURE 5.1 Calcium in action
In the field of biology, the removal of tissue cells from animals and subsequently culturing them in a Petri dish is a common practice. Cells adhere to each other like in tissue when they are placed in a culture dish.Just as human beings are social creatures who need other human beings, so cells need other cells, a process that relies entirely on calcium. Without calcium, the cells are unable to grow as quickly and their structures change. They isolate themselves and eliminate cell interaction.
Extracellular calcium is 20,000 times higher than intracellular calcium. However, the cell has internal complexes that also store calcium at 10–50 times the rate of the surrounding intracellular space. The wide disparity of calcium concentrations inside and outside the cell is due to the interactivity of calcium when it is not controlled. Most calcium inside the cell is attached to proteins and sequestered in internal cell complexes. On the planet earth, calcium cannot exist freely without interacting with something. Like the most respected member of a family, all important matters in the cell involve calcium.
Further calcium experiments were performed on muscle after Ringer’s famous experiments. Extracellular calcium can stop muscle contraction. When it drops below a certain level, muscles twitch uncontrollably. Calcium is also stored in neurons at the synapse. When the electrical signal reaches the end of the axon, calcium floods the synapse from the extracellular space like people into a store for a 50 percent off sale. The calcium “flux” causes a release of calcium from sequestered stores inside the cell and is required for transmitter release. Because the understanding of calcium in the cell came about later than Hodgkin and Huxley’s squid giant axon experiments, the belief is that calcium contributes to the electrical gradient more than previously expected.
In astrocytes, the main signaling comes from complexes inside the cell called “internal calcium stores.” Neurons require the electrical axon impulse for calcium influx from the extracellular space to enter at the synapse and affect transmitter release. External calcium influencing transmitter release has been shown to come from astrocytes.
In the short paper published by Murphy and colleagues, which showed that transmitters can institute a calcium increase in astrocytes, they were concerned with a single cell and did not understand the extent of astrocyte reception of neuronal communication. A neuron signaling to an astrocyte could carry information from our senses. If neurons are the only cell involved in mental processing, why would astrocytes respond to the sensory stimulus of neurons? At the point of their discovery, Murphy and his colleagues did not understand that astrocytes might also be able to signal to other astrocytes and to neurons themselves.
A couple papers from Yale, the first by Ann H. Cornell-Bell and colleagues in 1990, demonstrated that calcium waves occur in astrocytes when they are stimulated. After a transmitter acts on an astrocyte or a researcher mechanically stimulates the cell with an electrode—a long plastic tip about 1/200th of a millimeter wide—the calcium wave spreads from one astrocyte to the next. The spread is similar to what Golgi described—through physical connections between the star-like cells long arms—similar to billions of octopi holding hands.
The understanding of how the cells held hands began in 1969. Researchers at the National Institutes of Health, Milton Brightman and Thomas S. Reese, laid the foundation for what would be known as the gap junction. Looking at pictures taken with the electron microscope, they demonstrated that astrocytes—with the ends of their processes probing blood vessels and neuronal surfaces—also come into contact with
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