Abstract
Little is known about the native properties of unitary cardiac L-type
calcium currents (i(Ca)) 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 (gamma) to physiological Ca concentration and compare
it to barium ion (Ba) conductance in the absence of agonists. In
isolated, K-depolarized rat myocytes, i(Ca) 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 gammaCa of 5.3
+/- 0.2 pS (n = 15), and gammaBa of 15 +/- 1 pS (n = 27). The concentration
producing half-maximal gamma, Kd(gamma), 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.
- animals;
- barium,
- calcium
- calcium,
- cations,
- channel
- channels,
- conductivity;
- cytology/metabolism;
- divalent,
- dose-response
- drug
- drug;
- effects;
- electric
- gating,
- humans;
- ion
- l-type,
- male;
- membrane
- metabolism/pharmacology;
- metabolism;
- myocardium,
- patch-clamp
- potentials,
- rats,
- rats;
- relationship,
- sprague-dawley
- techniques;
- transport,
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