Cftr-dependent membrane insertion is linked to stimulation of the
cftr chloride conductance.
Takahashi, Akira, Simon C. Watkins, Marybeth Howard, and Raymond A.
Frizzell.
Department of Cell Biology and Physiology, University of Pittsburgh
School of Medicine, Pittsburgh, PA 15261
APStracts 3:0212C, 1996.
We examined the relation between Cl current (ICl) stimulation and cell
membrane capacitance (Cm) when CFTR was expressed in Xenopus oocytes.
ICl and Cm increased in parallel when oocytes expressing CFTR were
stimulated by forskolin (10 [mu]M) and IBMX (1 mM). The cAMP -
induced increase in surface area detected by Cm was confirmed by
morphometry in the same oocytes used for the electrical recordings.
These increases in ICl and Cm were reversible and were absent from
control oocytes not injected with CFTR cRNA. The time to reach peak
ICl lagged slightly behind the peak in Cm. ICl was varied by altering
CFTR expression level, agonist dose, or by expressing different CFTR
mutants. In all cases, there was a close correlation between ICl and
Cm, and the kinetics of ICl and Cm stimulation were more rapid the
larger the magnitude of the stimulated current. The Cm - ICl relation
for wt CFTR saturated, consistent with a limited capacity of cells to
increase their surface area. These results indicate that stimulation
of the CFTR Cl current is linked closely to increases in membrane
area. This suggests that CFTR is present in the membrane vesicles
whose insertion is stimulated by cAMP. The contents of these vesicles
may provide a link between activation of CFTR and its cAMP-dependent
regulation of other channels.
Received 17 May 1996; accepted in final form 19 June 1996.
APS Manuscript Number C274-6.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 4 July 96