Modulation of Ca2+ signaling by K+ channels in a hypothalamic neuronal cell line (GT1-1)

The pulsatile release of gonadotropin releasing hormone (GnRH) is driven by the intrinsic activity of GnRH neurons, which is characterized by bursts of action potentials correlated with oscillatory increases in intracellular Ca2+. The role of K+ channels in this spontaneous activity was studied by examining the effects of commonly used K+ channel blockers on K+ currents, spontaneous action currents, and spontaneous Ca2+ signaling. Whole-cell recordings of voltage-gated outward K+ currents in GT1-1 neurons revealed at least two different components of the current. These included a rapidly activating transient component and a more slowly activating, sustained component. The transient component could be eliminated by a depolarizing prepulse or by bath application of 1.5 mM 4-aminopyridine (4-AP). The sustained component was partially blocked by 2 mM tetraethylammonium (TEA). GT1-1 cells also express inwardly rectifying K+ currents (I-K(IR)) that were activated by hyperpolarization in the presence of elevated extracellular K+. These currents were blocked by 100 muM Ba2+ and unaffected by 2 mM TEA or 1.5 mM 4-AP. TEA and Ba2+ had distinct effects on the pattern of action current bursts and the resulting Ca2+ oscillations. TEA increased action current burst duration and increased the amplitude of Ca2+ oscillations. Ba2+ caused an increase in the frequency of action current bursts and Ca2+ oscillations. These results indicate that specific subtypes of K+ channels in GT1-1 cells can have distinct roles in the amplitude modulation or frequency modulation of Ca2+ signaling. K+ current modulation of electrical activity and Ca2+ signaling may be important in the generation of the patterns of cellular activity responsible for the pulsatile release of GnRH.