Biology Reference
In-Depth Information
channels for diltiazem (
33
). Here, further studies evaluating
expression and associated currents of all voltage-gated Ca
2+
chan-
nels in arterial myocytes are needed.
3.4. Other Factors
Infl uencing Ion
Channel Expression
Several factors besides subarachnoid blood have great infl uence on
ion channel expression and function and should therefore be
considered. Here, a fussy defi nition and declaration of the general
condition is crucial. Ion channel regulation is highly dynamically
regulated during maturation or in response of other external infl u-
ences (
4, 34-39
). Also yet not been studied for myocytes, several
examples have documented developmental changes of Ca
2+
chan-
nels, for example, in the calyx of Held, where transmission at early
developmental stages is mediated by a cooperative action of spa-
tially intermingled N-, P/Q-, and probably also R-type Ca
2+
chan-
nels and N- and R-type Ca
2+
channel are replaced by P/Q-type
calcium channels during maturation (
34, 35
). Similar changes
occur also in aging brains (
40
) and developmental changes have
also been documented for K
+
channels (
41
). Here, a study evaluat-
ing possible differences in ion channel expression after SAH at
different points of maturation might be interesting. Furthermore,
expression and function of ion channels are regulated by several
other parameters, like in response of several hormones, pain, etc.
(
42-45
). During planning of studies addressing ion channel expres-
sion, function or analysis of corresponding currents, those param-
eters infl uencing channel expression and function, like age of
animals, should be considered and defi ned.
Standard analysis of ion channel expression and of their mediated
currents focused yet on cerebral vessel myocytes. Assessment of ion
channel expression and dysfunction might also include other
vascular layers. Oxy-hemoglobin-induced apoptotic changes in
cultured vascular endothelial cells have been described; also they
could not be prevented by standard Ca
2+
channel blockers (
46
).
Furthermore, evaluation of alterations of ion channel expression
and function in the cerebral cortex in response to SAH might be
interesting and has yet not been investigated. One might speculate,
if subarachnoid bleed and its break-down products impair neuro-
logical transmission. For hippocampal CA1 neurons, such an infl u-
ence on neuronal transmission has not been found for hemoglobin
itself but for its degradation products ferrous chloride and hemin
which produce an irreversible depression of fi eld excitatory post-
synaptic potential (
47
).
3.5. Where Should Ion
Channel Assessment
Be Performed?
Besides analysis of ion channel expression, distribution and their
mediated currents, evaluation of their physiological and pathophys-
iological role is out of outstanding interest. Use of inhibitors
enables specifi c blockade of particular ion channels in the plasma
membrane and a subsequent analysis of their function and
3.6. Functional
Assessment of Ion
Channels by Specifi c
Blockade of Particular
Ion Channels
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