Calcium signaling, TRP channels and intracellular Ca2+ measurement in neurons

Year 2019, Cilt 11 Supp 1 (BRS), 1 - 1, 21.06.2019

Mustafa Nazıroglu

https://doi.org/10.37212/jcnos.583175

Abstract

Calcium ion (Ca²⁺)
has several physiological and pathophysiological functions such as communication,
cell death and development in neurons. Normally, Ca²⁺ concentration
is too high in out of the neurons (1-3 mM) as compared to the inside of the
neurons (50-100 nM). Ca²⁺ passes the cell membranes through passive and
active channels. Passive channels are leak channels. Well known active channels
are including several channels such as voltage gated channels, chemical
channels, store operated channels and mechanical channels (Kumar et al. 2014).  In addition, Ca²⁺ is released from
intracellular organelles to cytosol by activation IP₃ and ryanodine
receptors. Apart from the well-known cell membrane Ca²⁺ channels,
transient receptor potential (TRP) channels were discovered within the last
decades. The TRP channels have 28 members within the 6 subgroups in mammalian.
Activation and inhibition mechanisms of the TRP channels are very different
from the well-known Ca²⁺ channels. For example, TRP vanilloid 1
(TRPV1) channel is activated by hot chili pepper component (capsaicin), acidic
pH, high temperature and the vanilloids (Caterina et
al. 1997).  TRP melastatin 2 (TRPM2)
channel is activated by ADP-Ribose and NAD⁺. TRPM2 and TRPV1
channels are also activated by oxidative stress (Nazıroğlu and Braidy,
2017). In several neuronal diseases such as epilepsy and Alzheimer’s disease,
intracellular free Ca²⁺ concentration is increased by the oxidative
stress. Hence, measurement of intracellular free Ca²⁺ concentration
is very important for discovering new calcium channel blocker drugs. In the cytosol
of neurons, intracellular free Ca²⁺ concentration was measured by
using Ca²⁺ indicators.      

There are two
main classes of calcium indicators namely chemical indicators and genetically
encoded calcium indicators. Chemical indicators of free intracellular Ca²⁺
are Fura-2, Fluo-3, Fluo-4 and Rhod2. These dyes are often used with
acetoxymethyl esters, in order to render the molecule lyphophlilic and to allow
easy entrance into the cell. Genetically encoded indicators do not need to be
loaded into cells, instead the genes encoding for these proteins can be easily
transfected to cells. These indicators are fluorescent proteins derived from
green fluorescent protein (GFP). In this presentation, I will summarize Ca²⁺
signaling and using the fluorescent dyes for Ca²⁺ imaging.

In conclusion,
intracellular free Ca²⁺ concentration can be measured by using the
indicators. In the measurement techniques, laser confocal microscopy seems best
technique.

Keywords

Calcium signaling, apoptosis, neuron

References

• Caterina MJ, Schumacher MA, Tominaga M, Rosen TA, Levine JD, Julius D. 1997. The capsaicin receptor: a heat-activated ion channel in the pain pathway. Nature. 389(6653):816-24.
• Kumar VS, Gopalakrishnan A, Nazıroğlu M, Rajanikant GK. 2014. Calcium ion--the key player in cerebral ischemia. Curr Med Chem. 21(18):2065-2075.
• Nazıroğlu M, Braidy N. 2017 Thermo-sensitive TRP channels: Novel targets for treating chemotherapy-induced peripheral pain. Front Physiol. 8:1040.