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Growth hormone‐releasing peptide‐2 reduces inward rectifying K + currents via a PKA‐cAMP‐mediated signalling pathway in ovine somatotropes
Author(s) -
Xu Ruwei,
Zhao Yufeng,
Chen Chen
Publication year - 2002
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2002.030916
Subject(s) - somatotropic cell , chelerythrine , chemistry , protein kinase a , intracellular , patch clamp , medicine , endocrinology , biophysics , peptide , protein kinase c , receptor , microbiology and biotechnology , signal transduction , biology , biochemistry , hormone , kinase , pituitary gland
Inward‐rectifying potassium (Kir) channels are essential for maintaining the resting membrane potential near the K + equilibrium and they are responsible for hyperpolarisation‐induced K + influx. We characterised the Kir current in primary cultured ovine somatotropes and examined the effect of growth hormone‐releasing peptide‐2 (GHRP‐2) on this current and its related intracellular signalling pathways. The Kir current was, in most cases, isolated using nystatin‐perforated patch‐clamp techniques. In bath solution containing 5 m m K + , the Kir current was composed of both transient (fast activated) and delayed (slowly activated) components. An increase in the external K + concentration from 5 to 25 m m induced an augmentation of ≈4‐fold in the delayed part of the Kir current and both BaCl 2 and CsCl dose‐dependently inhibited this current, confirming the presence of the Kir current in ovine somatotropes. Moreover, this specific effect of high K + on the Kir current was only observed in the cells that showed positive staining with anti‐growth hormone (GH) antibodies, or in GC cells that belong to a rat somatotrope cell line. Application of GHRP‐2 (100 n m ) reversibly and significantly reduced the Kir current in bath solutions with 5 or 25 m m K + in ovine somatotropes. In addition, we found that the reduction in the Kir current mediated by GHRP‐2 was totally abolished by the pretreatments with H89 (1 μ m ) or Rp‐cAMP (100 μ m ) or by intracellular dialysis of a specific protein kinase A (PKA) inhibitory peptide PKI (10 μ m ). The specific PKC blocker chelerythrine (1 μ m ) or inhibitory peptide PKC 19‐36 (10 μ m ) did not show any effects on the GHRP‐2‐induced decrease in the Kir current. These results suggest that the inhibition of Kir current through PKA‐cAMP pathways may play an integral role in GHRP‐2‐induced depolarisation and GH release in ovine somatotropes.