Electrical Activity of Nerve Cells 
We are also interested in other nerve cell ion 
channels that are not primarily regulated by cal- 
cium. For example, we have recently been able to 
record directly the activity of a potassium ion 
channel that we had previously postulated and 
called the M channel. This channel operates in a 
membrane potential range (—60 to —30 mV) in 
which calcium entry is not important. Neverthe- 
less, agents (e.g., the neurotransmitter acetylcho- 
line and the widely consumed drug caffeine) that 
alfect intracellular calcium can also affect the M 
channel. In recent experiments we have used two 
different methods to raise intracellular calcium 
and explore this relationship. One method uses 
light to release calcium from a molecular cage; 
the other involves perfusing the cell interior with 
various calcium-buffer mixtures. Both ap- 
proaches show that M channel activity increases 
when calcium levels increase moderately above 
normal. Transmitters that decrease M channel ac- 
tivity must therefore work by some other, un- 
known, mechanism. 
We have also recently studied a neurotransmit- 
ter-operated synaptic channel in relay cells of the 
lateral geniculate nucleus (LGN). Excitatory 
synapses on LGN relay cells from both the eye 
and cerebral cortex activate voltage-dependent 
NMDA (7V-methyl-D-aspartate) channels. We are 
currently trying to understand the voltage-depen- 
dent responses of these cells. 
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