Nitric oxide (NO) electrochemical sensors - Electrochemical Sensors, Biosensors and Their Biomedical Applications - page 19

study a 30 m diameter carbon fi ber was coated with nickel tetrakis(3-methoxy-4-

hydroxyphenyl)porphyrin, via electrodeposition using differential pulse voltammetry,
and Nafi on. This electrode was then inserted into the cavernous bodies of a rat penis.
The results showed an increase in NO concentration, and intracavernous pressure,
upon cavernous nerve stimulation and a subsequent decrease upon the introduction of
NO synthase isoenzymes. This study was important to facilitate further measurements
of NO concentrations in vivo in the penis.
NO measurements have also been made in the ears of a guinea pig. The fi rst of these
studies was performed by Nuttall and coworkers in 2002 [113]. For this investigation
an ISONOP30 carbon fi ber electrode from WPI was inserted into the perilymph of the
basal turn of the guinea pig ear to measure changes in NO concentration as a result of
noise stimulation. This study showed that guinea pigs exposed to broadband noise for
3 h/day at 120 dBA, for 3 days, exhibited an increase in NO concentration in the peril-
ymph. This result is important in order to understand the role that NO plays in hearing
loss. A subsequent publication by Nuttall and coworkers used the ISONOP200 from
WPI to measure NO concentration in the spiral modiolar artery (SMA) of a guinea pig
[114]. This study is important to gain a better understanding of how NO potentially
regulates cochlear blood fl ow to set a benchmark for pharmacological and pathological
evaluation. To perform this study a 3 mm section of the SMA was added to a bath solu-
tion and the complete tip of the 200

µ

m electrode was inserted into the bath, parallel
to the SMA, to measure basal NO concentration as well as drug induced NO release
and how that relates to cochlear blood fl ow regulation. The key fi ndings of this study
were that the SMA continuously releases NO and that a blockage of this release by
L-NAME causes a decrease in NO production and a vasoconstriction. These fi ndings
are important in order to understand and interpret future fi ndings.
An interesting study was performed by Kashiwagi and coworkers studying the role
that NO plays in tumor vessel morphogenesis and maturation [105]. For this study,
B16 tumor cells were injected into mice and tumor tissue removed from the mice when
it reached

µ

8 mm in diameter. The tip of a Nafi on polymer coated Au microelectrode
was subsequently inserted into the tumor to monitor NO production. The results of this
study showed that NO mediates mural cell coverage and vessel branching/longitudinal
extension but does not play a part in the growth of tumor blood vessels. The investiga-
tors also used an NOS inhibitor to show that NOS from endothelial cells in tumors is
the primary source of NO and mediates tumor growth.
Kishi and coworkers used a commercial NO-selective microelectrode to monitor the
effect that exercise has on platelet-derived NO [110]. This study used 23 healthy male
non-smokers who underwent treadmill exercise. Blood samples were taken from the
subjects before and directly following exercise and blood platelets isolated. The study
showed that NO concentration and platelet levels were increased following exercise.
This increase in NO concentration is thought to play a role in the prevention of exer-
cise induced platelet activation in humans.
Kellogg and coworkers recently reported on the measurement of NO under the human
skin in response to heat stress. For this study a fl exible 200

µ m NO microelectrode from