Potassium Current Is Not Affected by Long-Term Exposure to Ghrelin or GHRP-6 in Somatotropes GC Cells

الملخص EN

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 Ca2+; this is determined from the intracellular reserves and by the entrance of Ca2+ 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 Cd2+ (1 mM) and tetrodotoxin (1 μm) 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 (IA) sensitive to 4-aminopyridine, which represents ~40% of the total outgoing current; a sustained component named delayed rectifier (IK), 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.