“Coupled” and “digital” single channel properties of IP3R calcium channels
Karol Ondrias* and Lubica Malekova
Ins Mol Physiol
& Genetics, Slovak Acad Sci,
*karol.ondrias@savba.sk
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The aim of our work was to look for
“coupled” IP3R calcium release channels from rat brain microsomes.
We incorporated the microsomes into bilayer lipid membrane
and used 53 mmol/l Ca2+
as an ion carrier. After application of 5 μmol/l
of IP3, single channel behavior was observed in 16
out of 71 experiments. After activation by IP3, we recognized three different behaviors of the IP3R channels. A.) A “digital” channel
behaviour. The channel after activation by 5 μmol/l of IP3 opened only once or twice
for a few ms and after that remained closed for more than one minute. Increased
concentration of IP3 up to 15 μmol/l
did not activate the channel. Conductance 1.2-1.5 pA and open time (a few
ms) of the “digital” channels were similar to the regular channels. B.) A
“classical” regular channel behavior. The channels
were regularly gated after application of 5 μmol/l IP3, and their activity was prolonged
for more than two minutes. C.) A “coupled” channel behavior.
The calcium channels after application of 5 μmol/l IP3 had double conductance of the
regular channels. The coupled channels were inhibited by
20 μmol/l Heparin. We supposed that
IP3R calcium channels had at least three different behaviors,
probably performing different physiological functions.