Figure 1. E-4031 blocks the inward-rectifying K⁺ current in lactotrophs from primary culture.

Membrane currents of three different lactotrophs (a-c) were recorded in 150 mM K⁺ external solution with the pulse protocol shown below the membrane currents in B. From a holding potential of -40 mV, the membrane potential was changed to between 40 and -120 mV in steps of 20 mV. Pulse duration, 1·5 s. To ‘fully activate’ erg channels, a 2 s prepulse to 20 mV was introduced and separated by a 0·5 s gap from the test pulse. This gap was used to avoid the registration of K⁺ tail currents mediated by K⁺ channels different from erg channels. Dotted lines in the current recordings denote zero current. A, control membrane currents selected for their different deactivation kinetics. B, membrane currents recorded in the same cells as in A in the presence of 10 μM E-4031. C, the E-4031-sensitive current, obtained by subtraction of the corresponding membrane current traces shown in B from those in A. D, current- potential relationship of the E-4031-sensitive currents shown in C. Peak current amplitudes (•) and current amplitudes at the end of the 1·5 s test pulses (▪) were plotted versus test pulse potential. Symbols are connected by straight lines.