A Calsequestrin-1 Mutation Associated with a Skeletal Muscle Disease Alters Sarcoplasmic Ca2+ Release
Fig 4
Recordings of action potentials and SK type Ca2+-activated K+ currents from myotubes.
(A) Rebound APs elicited by a hyperpolarizing current (-600 pA, 500 ms), followed by a pulse to zero current injection, in sample myotubes from a patient (red) and a control (black). (B) Currents, elicited in a control myotube by a pre-pulse to +20 mV, followed by repolarization to -40 mV. Tail currents are shown enlarged before (ctrl) and after apamin (apa) application (100 nM). The bar graph (inset) shows the fractional tail current before and after apamin application. (C) Membrane voltage traces recorded from sample control (black) and patient (red) myotubes, showing the hyperpolarizing effect of co-application of 100 μM of the SK channel activator DCEBIO and 2 μM of the Ca2+ ionophore agent ionomycin (indicated as DCEBIO/iono) in the recording chamber, without applying holding current. (D) Plot showing the mean membrane potential before (Vr) and after (Vr2) bath application of DCEBIO/iono, and the mean DCEBIO/iono induced hyperpolarization (ΔV) in control (black) and patient (red) myotubes. The data are mean±SEM; n = 6.