KCNMA1 and myotonic dystrophy type 1: Whole-cell patch-clamp analysis of myoblasts showed that the current density at the plasma membrane of normal myoblasts is higher than that of DM1 myoblasts above 160 mV (Figure 1e), a membrane potential range at which KCa1.1 opens in the absence of intracellular calcium.16 We next tested the effects of the nonselective potassium channel blocker tetraethylammonium (TEA) and of the selective KCa1.1 blocker paxilline17 on the currents elicited at 200 mV.