Voltage-dependent properties of macroscopic and elementary calcium
channel currents in guinea pig ventricular myocytes.
Pflugers Arch, 406 (5):
437--448 (мая 1986)Аннотация
Whole-cell Ca channel currents were recorded from guinea pig ventricular
myocytes that were internally perfused with Cs solution and bathed
in solutions containing 3.6 mM Ca, 3.6 mM Ba or 90 mM Ba (34 degrees
C). Single Ca channel currents were recorded from cell-attached membrane
patches of similar myocytes; the patch pipettes contained a 90 mM
Ba solution. 1. Although the shape of the whole-cell I-V relation
was independent of the bathing solution, this was not the case with
the location of the inward current maximum (Vpeak); Vpeak in 90 mM
Ba was about 30 mV positive to Vpeak in 3.6 mM Ba. 2. The activation
and inactivation of whole-cell currents were voltage dependent. Compared
to the voltage dependencies in 3.6 mM Ba, those in 90 mM Ba were
shifted by about 30 mV to the right, suggesting a neutralization
of surface charges. 3. Observations compatible with the ion permeation
model proposed by Hess and Tsien (1984) included (a) a depression
of current during Ca/Ba solution exchange, (b) a high divalent to
monovalent ion permeability, and (c) rectification of the outward
limb of the I-V relation. 4. Estimated current densities at Vpeak
were similar for myocytes in 3.6 mM Ca and 3.6 mM Ba, and about 10
times larger in 90 mM Ba. 5. Average currents (I) calculated from
ensembles of records of single Ca channel current had voltage-dependent
time courses resembling those of whole-cell IBa (90 mM). 6. Single-channel
I-V relations were superimposable on whole-cell I-V curves suggesting
that voltage-dependent single-channel parameters (probability of
opening, elementary current amplitude) can be related to the voltage-dependent
macroscopic current parameters (activation, instantaneous I-V relation)
when scaled by channel number. 7. The density of Ca channels in myocytes
was calculated from whole-cell IBa (90 mM) and average current through
single channels. The outcome, 3-5 channels/micron 2, agrees with
two other recent estimates (Tsien et al. 1983; Lux and Brown 1984).
However, it is difficult to reconcile with the much lower density
that one would forecast from the frequency of functional channel
observation in myocyte membrane patches (Pelzer et al. 1985c).
Описание
The whole bibliography file I use.