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Oxygen-sensitive reduction in Ca²⁺-activated K⁺ channel open probability in turtle cerebrocortex.
C I Rodgers-Garlick1, D W Hogg, L T Buck
1Department of Cell and Systems Biology, University of Toronto, Toronto, ON, Canada M5S 3G5.
Neuroscience
|February 7, 2013
Summary
Western painted turtles reduce brain metabolism during anoxia by decreasing neuronal firing. Researchers found oxygen-sensitive calcium-activated potassium channels (KCa) in turtle neurons, which decrease activity during anoxia, conserving energy.
Area of Science:
- Neuroscience
- Comparative Physiology
- Biophysics
Background:
- The western painted turtle brain reduces metabolic rate and neuronal activity under low oxygen (anoxia).
- This involves altered activity of N-methyl-D-aspartate (NMDA) and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors, and paradoxically, increased γ-aminobutyric acid (GABA) receptor currents.
- The role of other oxygen-sensitive ion channels in this adaptive response is not fully understood.
Purpose of the Study:
- To identify and characterize other oxygen-sensitive ion channels in the turtle brain.
- To investigate the role of calcium-activated potassium channels (KCa) in the anoxic response of turtle cortical neurons.
Main Methods:
- Single-channel recordings of KCa activity were performed using cell-attached and excised inside-out patch configurations on turtle cortical neurons.
- Neurons were bathed in artificial cerebrospinal fluid (aCSF) under normoxic or anoxic conditions.
- The effects of protein kinase C (PKC) modulators (chelerythrine and phorbol ester) on KCa channel activity were examined.
Main Results:
- A Ca(2+)-activated K(+) channel (KCa) with a slope conductance of 223pS was identified.
- In cell-attached mode, anoxia reversibly reduced KCa channel open probability (P(open)) by fivefold.
- PKC inhibition prevented the anoxia-induced decrease in P(open), while a PKC activator reduced P(open) under normoxia.
Conclusions:
- Turtle pyramidal cell KCa channels are oxygen-sensitive and regulated by intracellular factors.
- The anoxia-mediated decrease in KCa channel activity likely prevents excessive calcium influx and reduces energy expenditure.
- These channels are proposed as the reptilian counterparts of mammalian large-conductance Ca(2+)-activated K+ (BK) channels.
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