78 / 119
Emerging Concepts in Ion Channel Biophysics
Poster Abstracts
73
23-POS
Board 23
Mechanisms of Modulation of Voltage-gated Ca
2+
Channels by MDIMP
Juan A. De la Rosa
, Teresa Mancilla-Percino, Guillermo Avila.
Cinvestav IPN, Mexico City, Mexico.
Introduction: Recently, two series of isoindolines derived from α-aminoacids were synthesized
(containing either carboxylic or ester groups), and a theoretical analysis (molecular docking
studies) gave rise to the notion that these compounds might modulate voltage-gated Ca
2+
channels (VGCCs). More recently, voltage-clamp experiments in cardiac myocytes led to the
exciting discovery that an isoindoline ester derived from L-leucine (MDIMP) effectively
modulates VGCCs. Objective: Here we investigate whether this effect can be classified as “fast
and selective” for each subtype of cardiac VGCC. Methods: Ca
2+
currents were measured under
whole-cell patch-clamp conditions in heterologous expression systems. A fast perfusion system
was used, and the activity of VGCCs was measured in the absence and presence of extracellular
MDIMP (paired experiments). Results: Ca
V
1.2 (L-type channel) was investigated first. 250 µM
of MDIMP slowly decreased the magnitude of I
CaL
, reaching a maximum effect in ~10 min
(90%). Because of its slow nature, this phenomenon was not further studied. We then focused on
Ca
V
2.3 (R-type channel). Remarkably, MDIMP suddenly decreased the magnitude of I
CaR
(within 2-90 s) and the recovery phase was equally fast. This effect was more potent 200-ms
after depolarization compared with that estimated at the peak of the current (the IC
50
values
were: 78 µM and 557 µM). In fact, a drastic acceleration in the apparent inactivation rate was
also observed. Additional data indicate that MDIMP also rapidly inhibits Ca
V
3.1 (T-type
channel), with an IC
50
of 132 µM. This action, however, did not involve changes in the
activation and inactivation kinetics. Nevertheless, in both cases (Ca
V
2.3 and Ca
V
3.1) the steady-
state voltage dependence of inactivation was shifted (-42 mV and -13 mV), in the absence of
changes in activation curves. Conclusion: These data indicate that the mechanisms by which
MDIMP modulates VGCCs are channel-type specific.