THE EFFECTS OF LYOTROPIC ANIONS ON CHARGE MOVEMENT, CALCIUM CURRENTS AND CALCIUM SIGNALS IN FROG SKELETAL-MUSCLE FIBERS

1. Intramembrane charge movement and Ca2+ currents were monitored in voltage‐clamped segments of frog skeletal muscle fibres using the triple‐Vaseline‐gap technique. Calcium signals were measured in current‐clamped fibres using either of the indicators Arsenazo III or Antipyrylazo III. 2. Non‐linear capacitative currents (charge 1) were obtained using a subtraction procedure which employed either a ‐20 mV control pulse from a holding potential of ‐100 mV or alternatively a control pulse to +80 mV in depolarized fibres. The amount of charge mobilized depended on voltage according to a two‐state Boltzmann function. The total charge (Qmax) was increased by ca 100% and the steepness parameter (k) by ca 70% when a +80 mV control pulse was used. 3. Thiocyanate (SCN‐) and other lyotropic anions reversibly shifted the voltage dependence of mobilized charge towards negative potentials. Qmax was not significantly affected. ‘Off’ charge tails were greatly prolonged by lyotropic anions. 4. Extracellularly applied lyotropic anions affected the dihydropyridine‐sensitive Ca2+ current by shifting the I‐V relation toward more negative voltages and delaying deactivation of the tail currents. 5. The effects of lyotropic anions did not depend on whether the anion was introduced intracellularly or extracellularly. 6. Extracellular SCN‐ reversibly increased the peak amplitude and rate of rise of Ca signals, and decreased the latent period between stimulation and onset of the Ca signal. 7. It is concluded that lyotropic anions have similar effects on Ca2+ currents and on charge movement. © 1990 The Physiological Society