Requirement of GTP on somatostatin-induced K+ current in human pituitary tumor cells.

Abstract

The role of GTP on somatostatin-induced K+ current increase was examined in dissociated human pituitary tumor cells obtained from three acromegalic patients. Pituitary cells in culture were voltage-clamped by using the patch clamp technique in the whole-cell configuration. Somatostatin (100 nM) increased the membrane permeability to K+ ions and inhibited hormone secretion. A current-voltage relation of the somatostatin-induced K+ current showed an inward rectification when the concentration of extracellular K+ ions was increased.

Simultaneous Measurement of Changes in the Membrane Potential and the Intracellular Ca2+ Concentration Caused by Somatostatin in Human GH-Producing Pituitary Tumor Cells.

“…It was revealed that SRIF hyperpolarized the [2,6,14,20,22,23]. A similar membrane hyperpolarization has been reported in neurons [4,13] and atrial cells [10].…”

“…In human pituitary GH-producing cells, SRIF hyperpolarizes the membrane and thereby inhibits Ca2+-dependent spontaneous action potentials [22]. This membrane hyperpolarization is caused by a G-protein coupled K+ conductance increase [20,23]. A similar membrane hyperpolarization or K+ conductance increase has been reported in primary cultured rat somatotrophs, and clonal rat GH cells [2,6,14].…”

Different G proteins mediate somatostatin‐induced inward rectifier K+ currents in murine brain and endocrine cells

“…However, the type (or types) of PTX-sensitive G protein (Gi1, Gi2, Gi3 or Gï) involved in this SRIF effect has yet to be determined. In AtT-20 cells (a mouse pituitary tumour cell line) and in human pituitary tumour cells, SRIF activates an inward rectifier K¤ current, and this SRIF effect is also mediated by a PTX-sensitive G protein (Yamashita, Shibuya & Ogata, 1988;Pennefather, Heisler & MacDonald, 1988;Kozasa, Kaziro, Ohtsuka, Grigg, Nakajima & Nakajima, 1996). In AtT-20 cells as well, it has not yet been determined which one of several PTX-sensitive G proteins is involved in the SRIF effect.…”

Somatostatin activates glibenclamide‐sensitive and ATP‐regulated K+ channels in insulinoma cells via a G‐protein

“…It has been shown previously that somatostatin induces hyperpolarization in a corticotropinsecreting cell line and that this event is correlated with an activation of an inward rectifying K + conductance [12][13][14][15]. It will be important to see whether this K + channel is also ATP-regulated and sensitive to sulfonylureas.…”