The sources and sequestration of Ca2+ contributing to neuroeffector Ca2+ transients in the mouse vas deferens

• Published in: The Journal of physiology 2003-12, Vol.553 (2), p.627-635
• Main Authors: Brain, Keith L., Cuprian, Alina M., Williams, Damian J., Cunnane, Thomas C.
• Format: Article
• Language: English
• Subjects: Original
• ISSN: 0022-3751; 1469-7793
• DOI: 10.1113/jphysiol.2003.049734

The detection of focal Ca 2+ transients (called neuroeffector Ca 2+ transients, or NCTs) in smooth muscle of the mouse isolated vas deferens has been used to detect the packeted release of ATP from nerve terminal varicosities acting at postjunctional P2X receptors. The present study investigates the sources and sequestration of Ca 2+ in NCTs. Smooth muscle cells in whole mouse deferens were loaded with the Ca 2+ indicator Oregon Green 488 BAPTA-1 AM and viewed with a confocal microscope. Ryanodine (10 µ m ) decreased the amplitude of NCTs by 45 ± 6 %. Cyclopiazonic acid slowed the recovery of NCTs (from a time course of 200 ± 10 ms to 800 ± 100 ms). Caffeine (3 m m ) induced spontaneous focal smooth muscle Ca 2+ transients (sparks). Neither of the T-type Ca 2+ channel blockers NiCl 2 (50 µ m ) or mibefradil dihydrochloride (10 µ m ) affected the amplitude of excitatory junction potentials (2 ± 5 % and −3 ± 10 %) or NCTs (−20 ± 36 % and 3 ± 13 %). In about 20 % of cells, NCTs were associated with a local, subcellular twitch that remained in the presence of the α 1 -adrenoceptor antagonist prazosin (100 n m ), showing that NCTs can initiate local contractions. Slow (5.8 ± 0.4 µm s −1 ), spontaneous smooth muscle Ca 2+ waves were occasionally observed. Thus, Ca 2+ stores initially amplify and then sequester the Ca 2+ that enters through P2X receptors and there is no amplification by local voltage-gated Ca 2+ channels.