title: Potassium Current Is Not Affected by Long-Term Exposure to Ghrelin or GHRP-6 in Somatotropes GC Cells.
abstract: Ghrelin is a growth hormone (GH) secretagogue (GHS) and GHRP-6 is a synthetic peptide analogue; both act through the GHS receptor. GH secretion depends directly on the intracellular concentration of Ca(2+); this is determined from the intracellular reserves and by the entrance of Ca(2+) through the voltage-dependent calcium channels, which are activated by the membrane depolarization. Membrane potential is mainly determined by K(+) channels. In the present work, we investigated the effect of ghrelin (10 nM) or GHRP-6 (100 nM) for 96 h on functional expression of voltage-dependent K(+) channels in rat somatotropes: GC cell line. Physiological patch-clamp whole-cell recording was used to register the K(+) currents. With Cd(2+) (1 mM) and tetrodotoxin (1  μ m) in the bath solution recording, three types of currents were characterized on the basis of their biophysical and pharmacological properties. GC cells showed a K(+) current with a transitory component (I A) sensitive to 4-aminopyridine, which represents ~40% of the total outgoing current; a sustained component named delayed rectifier (I K), sensitive to tetraethylammonium; and a third type of K(+) current was recorded at potentials more negative than -80 mV, permitting the entrance of K(+) named inward rectifier (KIR). Chronic treatment with ghrelin or GHRP-6 did not modify the functional expression of K(+) channels, without significant changes (P < 0.05) in the amplitudes of the three currents observed; in addition, there were no modifications in their biophysical properties and kinetic activation or inactivation.
authors.affiliation: Laboratorio de Neuroendocrinología, Instituto de Fisiología, Benemérita Universidad Autónoma de Puebla, CP 7200, PUE, Mexico ; Laboratorio de Biología Celular, Facultad de Medicina Veterinaria y Zootecnia, Universidad Veracruzana, CP 91710, VER, Mexico.
authors.forename: Belisario
authors.initials: B
authors.lastname: Domínguez Mancera
authors.forename: Eduardo
authors.initials: E
authors.lastname: Monjaraz Guzman
authors.forename: Jorge L V
authors.initials: JL
authors.lastname: Flores-Hernández
authors.forename: Manuel
authors.initials: M
authors.lastname: Barrientos Morales
authors.forename: José M
authors.initials: JM
authors.lastname: Martínez Hernandez
authors.forename: Antonio
authors.initials: A
authors.lastname: Hernández Beltran
authors.forename: Patricia
authors.initials: P
authors.lastname: Cervantes Acosta