Calcium currents in human colonic smooth muscle cells .
Xiong, Zhiling, Nicholas Sperelakis, Amy Noffsinger & Cecilia
Fenoglio-Preiser.
Departments of Molecular and Cellular Physiology and Pathology and
Laboratory Medicine, University of Cincinnati College of Medicine,
Cincinnati, Ohio 45267
APStracts 2:0069G, 1995.
The voltage-gated Ca 2+ currents were investigated in single smooth
muscle cells freshly isolated from the circular layer of the human
colon (ascending and descending portions) using the whole-cell
voltage clamp technique. The tissue samples were obtained at the time
of therapeutic surgery. In physiological salt solution (containing 2
mM Ca2+), an inward current was observed when the cell membrane was
depolarized in the presence of tetrodotoxin. This current disappeared
when the Ca2+ ion was removed from the bath solution, and was
inhibited when Ca2+ channel blockers were applied, indicating that
the inward current was Ca2+ current (ICa). Changing the holding
potential (HP) from -100 mV to more positive potentials (e.g., -60
and -40 mV) markedly decreased the amplitude of I Ca. The voltage
dependence of steady-state activation and inactivation was
represented by Boltzmann distributions; there was a substantial
amount of overlap (window current) between -60 and -10 mV. A fast
-inactivating ICa component followed by a slow-inactivating ICa
component was observed in some cells from both ascending and
descending colons. The fast ICa component was observed only when the
cells were held at -80 mV or -100 mV, and had a more negative
threshold potential (-70 to -60 mV). This component was sensitive to
low concentration of Ni 2+ (30 [mu]M), but was resistant to
nifedipine (10 -20 [mu]M). In contrast, the slow (sustained) ICa
component was observed at all HPs (-40 to -100 mV), and had a more
positive threshold potential (ca. -40 mV). This component was
insensitive to low concentration of Ni2+, but was sensitive to
nifedipine and Bay K 8644. These results suggest that the fast
-inactivating (transient) current component might be a T-type Ca2+
current (ICa(T)), whereas the sustained component is an L-type Ca2+
current (ICa(L)). The current density of total ICa (L + T), ICa(L),
and ICa(T) declined with aging, but the decline in ICa(T) was less.
Received 31 August 1994; accepted in final form 25 March 1995.
APS Manuscript Number G331-4.
Article publication pending Am. J. Physiol. (Gastrointest. Liver
Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 25 April 1995.