Figure 1. Modulation of GH₃/B₆ cell erg currents by TRH.

Membrane currents were recorded in native GH₃/B₆ cells in the perforated-patch whole-cell configuration using isotonic KCl as external solution. From a holding potential of −80 mV, erg current activation was measured with 5 s depolarizing pulses to potentials between −80 and +40 mV followed by a constant hyperpolarizing pulse to −100 mV. The erg currents (Ac) were isolated as difference between the current traces recorded before (Aa) and after application of 10 μm E-4031 (Ab). B, mean normalized maximal erg current amplitudes elicited at repolarization to −100 mV as a function of the preceding test pulse potential before (○) and after (•) the application of 100 nm TRH. Data points were fitted with Boltzmann equations yielding the potentials of half-maximal activation (V_0.5). Scale bars, valid for current traces in both insets, denote 100 pA and 100 ms. C, shift in V_0.5 values of erg currents induced by the application of different concentrations of TRH. Number of experiments indicated, error bars denote s.e.m.;* and *** denote significant differences before and after TRH with P ≤ 0.05 and P ≤ 0.001, respectively; one-tailed paired t test. D, GH₃/B₆ cells express transcripts for rat erg1a, but not for erg1b. RT-PCR amplification products from the first and second round of amplification are shown. 20% (1 amplification, left side) or 10% (2 amplification, right side) of the PCR products were separated on a 1.5% agarose gel. Tissue origin of cDNAs used in the PCR reactions: rat brain (lanes 1, 2, 5, 6), GH₃/B₆ cells (lanes 3, 4, 7, 8). Amplification products of rat erg1a (1a) or rat erg1b (1b) are marked by arrows.