Figure 4.

Effects of external Cs⁺ and GnRH on inwardly rectifying K⁺ current and membrane excitability in GT1 cells. (A) Current–voltage relation of the inwardly rectifying K⁺ current before (○) and during (●) the application of 5 mM CsCl. Under perforated-patch voltage-clamp recording conditions, K_ir were activated by 1-sec hyperpolarizing voltage steps from –70 to –140 mV (holding potential = −40 mV). The mean current between 0.9 and 1 sec was measured and plotted against the V_m. (B) Simultaneous measurements of V_m and [Ca²⁺]_i during application of 5 mM CsCl. (C) I–V characteristics of the K_ir before (○) and during 100 nM GnRH application (●). (D) Simultaneous measurements of V_m and [Ca²⁺]_i in response to 100 nM GnRH (arrow) in the presence of 5 mM CsCl (bar).