Calcium and ph dependent halothane stimulation of calcium release
in sarcoplasmic reticulum from frog muscle.
Beltr[acute]an, Marianela, Ricardo Bull, Paulina Donoso, and Cecilia
Hidalgo.
Departamento de Fisiolog[acute]ia y Biof[acute]isica, Facultad de
Medicina, Universidad de Chile, Casilla 70005, Santiago 7, Chile,
Centro de Estudios Cient[acute]ificos de Santiago, Casilla 16443,
Santiago 9, Chile
APStracts 3:0099C, 1996.
The effect of halothane on calcium release kinetics was studied in
triad-enriched sarcoplasmic reticulum vesicles from frog skeletal
muscle. Release from vesicles passively equilibrated with 3 mM
45CaCl2 was measured in the millisecond time range using a fast
filtration system. Halothane 400 [mu]M increased release rate
constants at pH 7.1 and 7.4 as function of extravesicular pCa. In
contrast, halothane at pH 6.8 produced the same stimulation of
release in the pCa range 7.0 to 3.0; no release took place in these
conditions in the absence of halothane. Halothane shifted to the left
the calcium activation curve at pH 7.1, but not at pH 7.4, and
increased channel open probability at pH 7.1 in the cis pCa range 7.0
to 5.0. These results indicate that both cytosolic pCa and pH
modulate the stimulatory effects of halothane on calcium release.
Furthermore, halothane stimulated release in frog skeletal muscle at
low pH and resting [Ca2+], indicating that in frog muscle halothane
can override the closing of the release channels produced by these
conditions, as it does in malignant hyperthermia susceptible porcine
muscle.
Received 4 August 1995; accepted in final form 12 March 1996.
APS Manuscript Number C482-5.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 1 April 96