Figure 1. Blockade by dominant-negative Gα_q-QL/DN of the initial phase 1 of response induced by TRH in GH₃ cells.

A, effect of dominant-negative Gα_q on TRH-induced Phase 1 of hyperpolarization. Representative recordings of membrane potential are shown in two cells either expressing the dominant-negative form of Gα_q (lower trace) or not (upper trace). Application of 1 μm TRH is marked with a horizontal line on top of the traces. Note the maintenance of Phase 2 of increased electrical activity in the Gα_q-QL/DN-transfected cell. Traces averaged point by point from several cells are shown in the insets. Continuous current traces averaged point by point and their corresponding s.e.m. are shown. In this cases, traces were synchronized to the time of TRH addition as indicated with an arrow. B, effect of dominant-negative Gα_q and Gα₁₃ on Ca²⁺-dependent K⁺ currents elicited in GH₃ cells by TRH during the initial Phase 1 of response. Continuous current traces averaged point by point and their corresponding s.e.m. are shown for cells transfected with vector pcDNA3B (Control 3B), or with plasmids codifying the dominant-negative mutants of Gα_q (Gα_q-QL/DN) and Gα₁₃ (Gα₁₃-QL/DN). Traces were synchronized to the time of 1 μm TRH addition as indicated with an arrow. High-K⁺, low-Ca²⁺ extracellular solution and a potential of −30 mV were used for better detection of inward K⁺ currents activated by Ca²⁺ released from intracellular stores via IP₃.