Figure 6.
The T-window Ca2+ current is large enough to induce a change in [Ca2+]i. Myotubes had a mean capacitance of 160 ± 28 pF. Ca2+ (1.8 mM) was used as the charge carrier. The main graph represents the mean 405 nm/485 nm indo-1 ratio variations of five small myotubes during three different voltage steps. The cells were stepped at −75 mV (squares), −55 mV (circles), and −35 mV (triangles) for 75 s because it is the required time for [Ca2+]i to reach a steady-state. Maximum ratio increases during the step to −35 mV were normalized to 1. Continuous and dashed lines are decaying exponential fitted to the data points. (Inset) Indo-1 fluorescence ratios were evaluated during the last 10 s of the three voltage steps. Closed symbols represent the [Ca2+]i in control conditions, and open symbols the [Ca2+]i when mibefradil (10 μM) was added. Same five cells as main graph. Note that mibefradil was used rather than amiloride or Ni2+ because these agents affected the fluorescent signal of the extracellular solution.