TY - JOUR T1 - Potentiation of High Voltage–Activated Calcium Channels by 4-Aminopyridine Depends on Subunit Composition JF - Molecular Pharmacology JO - Mol Pharmacol SP - 760 LP - 772 DO - 10.1124/mol.114.095505 VL - 86 IS - 6 AU - Li Li AU - De-Pei Li AU - Shao-Rui Chen AU - Jinjun Chen AU - Hongzhen Hu AU - Hui-Lin Pan Y1 - 2014/12/01 UR - http://molpharm.aspetjournals.org/content/86/6/760.abstract N2 - 4-Aminopyridine (4-AP, fampridine) is used clinically to improve neuromuscular function in patients with multiple sclerosis, spinal cord injury, and myasthenia gravis. 4-AP can increase neuromuscular and synaptic transmission by directly stimulating high voltage–activated (HVA) Ca2+ channels independent of its blocking effect on voltage-activated K+ channels. Here we provide new evidence that the potentiating effect of 4-AP on HVA Ca2+ channels depends on the specific combination of voltage-activated calcium channel α1 (Cavα1) and voltage-activated calcium channel β (Cavβ) subunits. Among the four Cavβ subunits examined, Cavβ3 was the most significant subunit involved in the 4-AP–induced potentiation of both L-type and N-type currents. Of particular note, 4-AP at micromolar concentrations selectively potentiated L-type currents reconstituted with Cav1.2, α2δ1, and Cavβ3. In contrast, 4-AP potentiated N-type currents only at much higher concentrations and had little effect on P/Q-type currents. In a phrenic nerve–diaphragm preparation, blocking L-type Ca2+ channels eliminated the potentiating effect of low concentrations of 4-AP on end-plate potentials. Furthermore, 4-AP enhanced the physical interaction of Cav1.2 and Cav2.2 subunits to Cavβ3 and also increased their trafficking to the plasma membrane. Site-directed mutagenesis identified specific regions in the guanylate kinase, HOOK, and C-terminus domains of the Cavβ3 subunit crucial to the ability of 4-AP to potentiate L-type and N-type currents. Our findings indicate that 4-AP potentiates HVA Ca2+ channels by enhancing reciprocal Cav1.2-Cavβ3 and Cav2.2-Cavβ3 interactions. The therapeutic effect of 4-AP on neuromuscular function is probably mediated by its actions on Cavβ3-containing L-type Ca2+ channels. ER -