Gating of L-type Ca2+ channels in embryonic chick ventricle cells: dependence on voltage, current and channel density

• Published in: The Journal of physiology Vol. 443; no. 1; pp. 307 - 334
• Main Authors: Mazzanti, M, DeFelice, L J, Liu, Y M
• Format: Journal Article
• Language: English
• Published: Oxford The Physiological Society 01-11-1991; Blackwell
• Subjects: Animals; Barium - pharmacology; Biological and medical sciences; Calcium Channels - physiology; Chick Embryo; Embryology: invertebrates and vertebrates. Teratology; Fundamental and applied biological sciences. Psychology; Heart Ventricles; Ion Channel Gating - physiology; Kinetics; Membrane Potentials; Models, Biological; Nifedipine - pharmacology; Organogenesis. Fetal development; Organogenesis. Physiological fonctions; Phosphorylation; Heart; Vertebrata; Embryo; Calcium; Electrophysiology; Heart ventricle; Ionic channel; Chicken; Circulatory system; Ionic current; Aves
• ISSN: 0022-3751; 1469-7793
• DOI: 10.1113/jphysiol.1991.sp018835

1. L-type calcium channels in embryonic chick heart ventricle have voltage-dependent, time-variant kinetics when they conduct
inward currents carried by 20 mM-Ba2+. Depolarizing the membrane from -20 to 20 mV increases mean open time from 1.4 to 4.2
ms. Mean open time increases monotonically with voltage. The single-channel conductance, 18 +/- 2 pS, is approximately linear
over this voltage range, and the extrapolated reversal potential is 38 +/- 5 mV. 2. In cell-attached patches with five or
more L-type Ca2+ channels in the patch, the currents elicited by 500 ms depolarizing steps, from a -80 mV holding potential,
inactivate rapidly and have large tail currents. In the same patch, currents from a -40 mV holding potential are smaller,
inactivate more slowly, and have practically no tail currents. 3. In cell-attached patches containing one of two L-type Ca2+
channels, currents from -80 or -40 mV are virtually identical, and they are similar to the currents from multichannel patches
held at -40 mV. 4. The voltage-dependent, time-variant kinetics of individual L-type Ca2+ channels are unaltered if the patch
is removed from the cell and forms an inside-out configuration. In these experiments the internal membrane was bathed with
an artificial, intracellular-like solution containing no phosphorylating enzymes or substrates. 5. Cells bathed in 20 mM-Ba2+
solutions and held at -80 mV have currents with an early phase that inactivates in tens of milliseconds, a late phase that
inactivates in hundreds of milliseconds, and a large, slow tail current. Currents from -40 mV have only the late phase and
practically no tails. However, if the maximum current is less than 0.1 pA pF-1, records from either -80 or -40 mV are virtually
identical, and they are similar to currents from cells with higher channel density held at -40 mV. Furthermore, if cells are
stimulated before full recovery from inactivation, the reduced current is accompanied by slower inactivation. 6. Whole-cell
currents in 1.5 mM-Ca2+ solutions are entirely abolished by addition of 20 microM-nifedipine, and they are enhanced 2-3 times
by addition of 30 microM-cyclic AMP and 3 mM-ATP to the whole-cell recording electrode. The whole-cell currents in 20 mM-Ba2+
solutions are also completely blocked by 20 microM-nifedipine, regardless of kinetics or holding potential. Thus, by definition,
the cells we are studying contain only L-type channels.