Interaction of three structurally distinct Ca2+ channel activators with single L-type Ca2+ channels

Abstract

The dihydropyridine S(-)-Bay K 8644 (Bay K), the benzoylpyrrole FPL 64176 (FPL) and the benzodiazocine CGP 48506 (CGP) are structurally unrelated L-type Ca2+ channels agonists. The aim of our study was to investigate whether these three drugs interact with different binding sites and thereby modulate the behaviour of L-type Ca2+ channels in a qualitatively different manner. Single-channel recordings were performed on CHO cells stably expressing the alpha1C-b subunit of the L-type Ca2+ channel. Mean open time and open probability were determined sweep by sweep and the effects of CGP (10(-4) M), Bay K (10(-6) M) and FPL (10(-6) M) were compared. All three compounds increased mean open time and open probability when applied alone. However, the gating pattern changes induced by each drug were qualitatively and quantitatively different. We also applied binary mixtures and analysed the resulting sweeps with respect to their gating pattern. The application of mixtures did result in a gating pattern not seen with any of the single drugs. The mixture of CGP and FPL led to a prolonged mean open time compared with each single drug. The mixture of Bay K and FPL exhibited an open probability lower than with each single drug. The mixture of CGP and Bay K increased the mean open time per sweep like Bay K, but the number of openings was similar to the level seen with CGP alone. These results cannot be explained by assuming alternative binding of the drugs to a single binding site. We therefore conclude that Bay K, CGP and FPL bind to different but interacting sites on the L-type Ca2+ channel.

Cardiac L-type Calcium Channel β-Subunits Expressed in Human Heart Have Differential Effects on Single Channel Characteristics

“…As with Ca v 1.2a, non-transfected cells and cells cotransfected only with pcDNA3.1, ␣ 2 ␦-subunits, and GFP displayed a quite sparse pattern of activity of Ca v 1.2b (Fig. 5), similar to our previous observations (26).…”

Activation of cardiac ryanodine receptors by the calcium channel agonist FPL-64176

“…FPL did not affect [ 3 H]PN 200-110 binding; thus DHPs and FPL are thought to bind to different sites on the channel protein (16,23). However, electrophysiological evidence showed that singlechannel open probability (P o ) for a BAYK-FPL mixture exhibited a lower P o than either alone (11). This result was interpreted to suggest that although these agents bind to different sites on the Ca 2ϩ channel, a functional or physical interaction does in fact exist between them.…”

“…FPL is structurally unrelated to DHPs and is thought to bind to a separate site from DHPs on the I Ca,L in a noncompetitive manner (1,4,15,16,23). However, several reports (11,15,22) suggest that there is an allosteric interaction between the binding sites for FPL and DHPs even if they do not share a common receptor on the channel protein itself. Thus there is already evidence for interactions between binding sites in I Ca,L for the two classes of agonist.…”

Facilitation of L-Type Ca2+Channels in Dendritic Spines by Activation of β2Adrenergic Receptors

“…Gating mode 2 can be induced by L-type VDCC activators, stimulation of ␤-ARs (Yue et al, 1990), and through association of L-type channels with CaMKII (calcium/ calmodulin-dependent protein kinase II) (Dzhura et al, 2000). Whereas L-type VDCC activators cause more Ca 2ϩ influx as a result of a shift to mode 2 (Hess et al, 1984;Lauven et al, 1999), L-type channel blockers typically cause a stabilization of mode 0 (Hess et al, 1984).…”