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Biophys J, June 2001, p. 2742-2750, Vol. 80, No. 6
Laboratory of Cardiovascular Sciences, Gerontology Research Center, National Institute on Aging, National Institutes of Health, Baltimore, Maryland 21224 USA
Little is known about the native properties of unitary
cardiac L-type calcium currents (iCa) measured with
physiological calcium (Ca) ion concentration, and their role in
excitation-contraction (E-C) coupling. Our goal was to chart the
concentration-dependence of unitary conductance (
) to physiological
Ca concentration and compare it to barium ion (Ba) conductance in the
absence of agonists. In isolated, K-depolarized rat myocytes,
iCa amplitudes were measured using cell-attached patches
with 2 to 70 mM Ca or 2 to 105 mM Ba in the pipette. At 0 mV, 2 mM of
Ca produced 0.12 pA, and 2 mM of Ba produced 0.19 pA unitary currents.
Unitary conductance was described by a Langmuir isotherm relationship
with a maximum Ca of 5.3 ± 0.2 pS
(n = 15), and Ba of 15 ± 1 pS
(n = 27). The concentration producing half-maximal
, Kd(
), was not different
between Ca (1.7 ± 0.3 mM) and Ba (1.9 ± 0.4 mM). We found
that quasi-physiological concentrations of Ca produced currents that
were as easily resolvable as those obtained with the traditionally used
higher concentrations. This study leads to future work on the molecular
basis of E-C coupling with a physiological concentration of Ca ions
permeating the Ca channel.
Biophys J, June 2001, p. 2742-2750, Vol. 80, No. 6
© 2001 by the Biophysical Society 0006-3495/01/06/2742/09 $2.00
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