Emerging Concepts in Ion Channel Biophysics

Emerging Concepts in Ion Channel Biophysics

Poster Abstracts

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.

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