Physiologic gating properties of unitary cardiac L-type Ca2+ channels.

The contraction of adult mammalian ventricular cardiomyocytes is triggered by the influx of Ca(2+) ions through sarcolemmal L-type Ca(2+) channels (LCCs). However, the gating properties of unitary LCCs under physiologic conditions have remained elusive. Towards this end, we investigated the voltage-dependence of the gating kinetics of unitary LCCs, with a physiologic concentration of Ca(2+) ions permeating the channel.

Ca(2+)-dependent components of inactivation of unitary cardiac L-type Ca(2+) channels.

A Ca(2+) ion-dependent inactivation (CDI) of L-type Ca(2+) channels (LCC) is vital in limiting and shaping local Ca(2+) ion signalling in a variety of excitable cell types. However, under physiological conditions the unitary LCC properties that underlie macroscopic inactivation are unclear. Towards this end, we have probed the gating kinetics of individual cardiac LCCs recorded with a physiological Ca(2+) ion concentration (2 mM) permeating the channel, and in the absence of channel agonists.

Modulation of the conductance of unitary cardiac L-type Ca(2+) channels by conditioning voltage and divalent ions.

The accompanying paper (Josephson, I. R., A.

Modulation of the gating of unitary cardiac L-type Ca(2+) channels by conditioning voltage and divalent ions.

Although a considerable number of studies have characterized inactivation and facilitation of macroscopic L-type Ca(2+) channel currents, the single channel properties underlying these important regulatory processes have only rarely been examined using Ca(2+) ions. We have compared unitary L-type Ca(2+) channel currents recorded with a low concentration of Ca(2+) ions with those recorded with Ba(2+) ions to elucidate the ionic dependence of the mechanisms responsible for the prepulse-dependent modulation of Ca(2+) channel gating kinetics. Conditioning prepulses were applied across a wide range of voltages to examine their effects on the subsequent Ca(2+) channel activity, recorded at a constant test potential.

Alterations in properties of L-type Ca channels in aging rat heart.

Previous studies of whole-cell L-type Ca currents in aging heart have demonstrated an increase in the peak Ca current magnitude in proportion to the increase in membrane area, and a slowing of the time course for inactivation. However, the single-channel mechanisms underlying this upregulation, and for the slowed inactivation are not known. We have therefore compared the properties of single L-type Ca channel currents recorded from ventricular myocytes obtained from young adult (3 month), adult (6-8 month) and aging (24 month) Wistar rats, using 5 m m Ba ions as the permeant ion.

Ca(2+) signaling in cardiac myocytes overexpressing the alpha(1) subunit of L-type Ca(2+) channel.

Voltage-gated L-type Ca(2+) channels (LCCs) provide Ca(2+) ingress into cardiac myocytes and play a key role in intracellular Ca(2+) homeostasis and excitation-contraction coupling. We investigated the effects of a constitutive increase of LCC density on Ca(2+) signaling in ventricular myocytes from 4-month-old transgenic (Tg) mice overexpressing the alpha(1) subunit of LCC in the heart. At this age, cells were somewhat hypertrophic as reflected by a 20% increase in cell capacitance relative to those from nontransgenic (Ntg) littermates.