Re: What mammalian cell gives off the greatest action potential?

Your question has a number of parts, and they need to be answered that way, 
so this may be long.

First, your main question is: "What mammalian cell gives off the greatest 
action potential?"  The short answer is that all mammalian cells give off 
approximately the same size action potential, because they all fire action 
potentials the same way.

Action potentials, the large, fast electrical signals neurons use to 
communicate, work in a way that is common to all animals with nerve cells.  
If you're in a class that's trying to culture neurons, you know that in 
general, neurons maintain a resting potential of about -60 to -70 
millivolts (mV).  They do this in part by actively pumping in two potassium 
ions for every 3 sodium ions they pump out.  When an action potential is 
initiated, channels open up in the neuron to allow ions to flow.  Things 
will only flow if there is some force that makes them flow.  This force can 
be gravity, a concentration difference, or an electrical gradient.  First, 
sodium ions flow into the cell.  When the inside of the cell goes from -60 
or -70 mV to 0 mV, there is no longer an electrical gradient between the 
inside and the outside of the cell (it's zero mV on both sides of the 
membrane), so sodium ions stop flowing.  Then, potassium channels open, and 
because the concentration difference is so great between the inside and 
outside of the cell, potassium ions flow out, and the potential of the cell 
becomes negative again (positive ions flowing out is the same, 
electrically, as negative ions flowing in).  So the bottom line is that if 
all neurons use this same method for firing action potentials, they will 
all fire the same size action potential.  With rare exceptions this is true 
for all nerve cells - in humans, mice, and even squid.

Now, the second part of your question, which is, to paraphrase, "What type 
of neuron or other cell can we grow alone on a plate so that we can measure 
its action potential?"  There is a short answer to this one, too: neurons 
will not live or grow on a plate without their support cells, which are 
called glia.  Neurons are very complicated and metabolically active, even 
for a cell.  They absolutely require a special plating medium with glia, or 
support cells, on it so that they can fire action potentials.  You may be 
able to use other cells to test your sensor, but I don't know what type of 
sensor it is, or how it measures things, so I cannot address that issue 
directly.

The core problem is that there are lots of things I don't know about your 
experiment which make it difficult for me to help you.  Also, to be honest, 
as undergraduates designing such a complicated machine to measure action 
potentials, there are resources other than the Mad Scientist Network that 
you can, and should, use to help you answer your question.  First, about 
the specific type of cell that may be best suited to your experiment: there 
are many companies that sell plates and culture media and cell lines.  They 
all have help/customer support desks that are free.  They will be able to 
ask the right questions to help you find the proper cell line, and they can 
take price into consideration.  They also have researchers who can help you 
do things properly - plating and recording from neurons is very difficult 
to do, and you will need expert advice and help along the way.  Another 
resource is researchers at your university that culture cell lines.  They 
will have specific information and resources for doing this experiment as 
well.  As I said before, culturing cells such as neurons can be difficult, 
and will require expert assistance.

If you have other questions, or wish to ask me further questions about this 
project, I'll be happy to answer them.

Brenda