The effects of cyclopiazonic acid on cycloplasmic ca2+
concentration and membrane currents in guinea-pig urinary bladder
myocytes.
Yoshikawa, Akiyoshi, Cornelis Van Breemen, and Gerrit Isenberg.
Wakayam Medical College, Department of Cardiology, Internal
Medicine, Wakayama City, Japan
APStracts 3:0085C, 1996.
The effects of cyclopiazonic acid (CPA), an inhibitor of the
sarcoplasmic reticulum (SR) Ca2+ ATPase (SERCA), on cytosolic Ca2+
concentration ([Ca2+]c) and membrane currents were studied in
isolated urinary bladder myocytes with the objective of identifying
roles for SERCA in the regulation of [Ca2+]c and membrane potential.
At 36 oC and 3.6 mM [Ca2+]o, 10 [mu]M CPA was applied by rapid bath
application and [Ca2+]c was ratiometrically estimated from indo-1
fluorescence (100 [mu]M K5indo-1 in the pipette). Inhibition of SERCA
by CPA was demonstrated by the following modifications of the
caffeine-induced [Ca2+]c transients: a) CPA prolonged the 90% decay
time from peak to resting [Ca2+]c from 2.2+/-0.3s to 8.3+/-0.92s
(n=5). b) CPA abolished the "undershoot" of the [Ca2+]c
transient that follows the washout of caffeine. c) CPA prevented
caffeine from inducing a second [Ca2+]c transient suggesting that
Ca2+ refilling of the SR was inhibited.
Received 18 September 1995; accepted in final form 22 February
1996.
APS Manuscript Number C559-5.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 27 March 96