Photo-released intracellular Ca2+ rapidly blocks Ba2+ current in Lymnaea neurons. Johnson, B. D. & Byerly, L. The Journal of Physiology, 462(1):321–347, Wiley Online Library, mar, 1993.
Photo-released intracellular Ca2+ rapidly blocks Ba2+ current in Lymnaea neurons. [link]Paper  doi  abstract   bibtex   
1. The effect of intracellular Ca2+ on Ba2+ current flowing through voltage‐dependent Ca2+ channels was studied using the whole‐cell patch‐clamp technique on isolated neurons from the snail Lymnaea stagnalis. Intracellular Ca2+ was increased by flash photolysis of the caged Ca2+ compound DM‐nitrophen and measured with the optical indicator fluo‐3. 2. After the highest intensity flashes, peak Ba2+ current was blocked by 42% with a time constant of 5 ms. The onset of the block followed a similar time course whether channels were activated or closed. The Ba2+ current surviving after the flash had the same voltage dependence of activation and rate of inactivation as did the total Ba2+ current before the flash. 3. Recovery of the Ba2+ current from block was nearly complete and occurred with a time constant of 16 s. Multiple episodes of photolysis‐induced block could be studied in the same cell when 7‐10 min were allowed between flashes. In some cells, recovery from block was accompanied by a transient enhancement of the current above the pre‐block magnitude. 4. Neurons greatly reduced the ability of photolysis to increase Ca2+, both by unloading the DM‐nitrophen before flashes were applied and by rapidly buffering the photolytically released Ca2+. Maximal flashes on extracellular droplets of the DM‐Ca2+ solution created a Ca2+ jump from 110 nM to 40 microM. In contrast, the same flashes on DM‐Ca(2+)‐loaded neurons resulted in a Ca2+ transient starting from a baseline of 36 nM to a peak of 130 nM. This intracellular Ca2+ transient decayed with three time constants (120 ms, 2 s and 13 s). 5. Endogenous buffer(s) binds Ca2+ rapidly. When intracellular Ca2+ was monitored within 2 ms of the flash, no rapid Ca2+ spike due to binding of photo‐released Ca2+ could be detected. Addition of dibromo‐BAPTA to the intracellular solution reduced the block by one third, which is consistent with the measured reduction of intracellular Ca2+. This indicates that the endogenous buffer can bind Ca2+ as rapidly as dibromo‐BAPTA and as fast as Ca2+ is released by photolysis. 6. The Ca2+ dependence of the block, obtained by varying flash intensity, indicates some saturation by 130 nM. A simple two‐state model of the block consistent with both the time course of block and recovery and the concentration dependence gave a dissociation constant of approximately 50 nM and forward rate constant of 7 x 10(8) M‐1 s‐1.(ABSTRACT TRUNCATED AT 400 WORDS) \textcopyright 1993 The Physiological Society
@article{pop00672,
abstract = {1. The effect of intracellular Ca2+ on Ba2+ current flowing through voltage‐dependent Ca2+ channels was studied using the whole‐cell patch‐clamp technique on isolated neurons from the snail Lymnaea stagnalis. Intracellular Ca2+ was increased by flash photolysis of the caged Ca2+ compound DM‐nitrophen and measured with the optical indicator fluo‐3. 2. After the highest intensity flashes, peak Ba2+ current was blocked by 42{\%} with a time constant of 5 ms. The onset of the block followed a similar time course whether channels were activated or closed. The Ba2+ current surviving after the flash had the same voltage dependence of activation and rate of inactivation as did the total Ba2+ current before the flash. 3. Recovery of the Ba2+ current from block was nearly complete and occurred with a time constant of 16 s. Multiple episodes of photolysis‐induced block could be studied in the same cell when 7‐10 min were allowed between flashes. In some cells, recovery from block was accompanied by a transient enhancement of the current above the pre‐block magnitude. 4. Neurons greatly reduced the ability of photolysis to increase Ca2+, both by unloading the DM‐nitrophen before flashes were applied and by rapidly buffering the photolytically released Ca2+. Maximal flashes on extracellular droplets of the DM‐Ca2+ solution created a Ca2+ jump from 110 nM to 40 microM. In contrast, the same flashes on DM‐Ca(2+)‐loaded neurons resulted in a Ca2+ transient starting from a baseline of 36 nM to a peak of 130 nM. This intracellular Ca2+ transient decayed with three time constants (120 ms, 2 s and 13 s). 5. Endogenous buffer(s) binds Ca2+ rapidly. When intracellular Ca2+ was monitored within 2 ms of the flash, no rapid Ca2+ spike due to binding of photo‐released Ca2+ could be detected. Addition of dibromo‐BAPTA to the intracellular solution reduced the block by one third, which is consistent with the measured reduction of intracellular Ca2+. This indicates that the endogenous buffer can bind Ca2+ as rapidly as dibromo‐BAPTA and as fast as Ca2+ is released by photolysis. 6. The Ca2+ dependence of the block, obtained by varying flash intensity, indicates some saturation by 130 nM. A simple two‐state model of the block consistent with both the time course of block and recovery and the concentration dependence gave a dissociation constant of approximately 50 nM and forward rate constant of 7 x 10(8) M‐1 s‐1.(ABSTRACT TRUNCATED AT 400 WORDS) {\textcopyright} 1993 The Physiological Society},
annote = {Query date: 2020-06-29 13:05:30},
author = {Johnson, B. D. and Byerly, L.},
doi = {10.1113/jphysiol.1993.sp019558},
issn = {00223751},
journal = {The Journal of Physiology},
month = {mar},
number = {1},
pages = {321--347},
publisher = {Wiley Online Library},
title = {{Photo-released intracellular Ca2+ rapidly blocks Ba2+ current in Lymnaea neurons.}},
url = {https://physoc.onlinelibrary.wiley.com/doi/abs/10.1113/jphysiol.1993.sp019558 http://doi.wiley.com/10.1113/jphysiol.1993.sp019558},
volume = {462},
year = {1993}
}

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