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Modulation of voltage‐dependent Ba 2+ currents in the guinea‐pig gastric antrum by cyclic nucleotide‐dependent pathways
Author(s) -
Zhu HaiLei,
Hirst G David S,
Ito Yushi,
Teramoto Noriyoshi
Publication year - 2005
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1038/sj.bjp.0706295
Subject(s) - forskolin , protein kinase a , cyclic nucleotide , sodium nitroprusside , guinea pig , medicine , biophysics , endocrinology , chemistry , patch clamp , antrum , phosphodiesterase 3 , biology , kinase , nucleotide , biochemistry , receptor , stomach , nitric oxide , stimulation , gene
We have investigated whether the activation of cAMP‐ and cGMP‐dependent pathways modifies the properties of voltage‐dependent Ba 2+ currents ( I Ba ) recorded from guinea‐pig gastric myocytes using patch‐clamp techniques. All experiments were carried on single smooth muscle cells, dispersed from the circular layer of the guinea‐pig gastric antrum. Both dibutyryl cAMP (db‐cAMP, 0.1–1 m M ), a membrane‐permeable ester of cAMP, and isoproterenol, a selective β ‐stimulant, inhibited I Ba in a concentration‐dependent manner. Forskolin, but not dideoxy‐forskolin, an inactive isomer of forskolin, inhibited the peak amplitude of I Ba . In the presence of either Rp‐cAMP or the PKA (cAMP‐dependent protein kinase) inhibitor peptide 5‐24 (PKA‐IP), neither forskolin nor db‐cAMP inhibited I Ba . After establishing a conventional whole‐cell recording, the peak amplitude of I Ba gradually decreased when the catalytic subunit of PKA was included in the pipette. The further application of Rp‐cAMP reversibly enhanced I Ba . Sodium nitroprusside (0.1–1 m M ) and 8‐Br‐cGMP (0.1–1 m M ) also inhibited I Ba in a concentration‐dependent manner. The inhibitory effects of forskolin or db‐cAMP on I Ba were not significantly changed by pretreatment with a cGMP‐dependent protein kinase (PKG) inhibitor. Similarly, the inhibitory actions of 8‐Br‐cGMP on I Ba were not modified by PKA‐IP. The membrane‐permeable cyclic nucleotides db‐cAMP and 8‐Br‐cGMP caused little shift of the voltage dependence of the steady‐state inactivation and reactivation curves. Neither of the membrane‐permeable cyclic nucleotides db‐cAMP or 8‐Br‐cGMP had additive inhibitory effects on I Ba . These results indicate that two distinct cyclic nucleotide‐dependent pathways are present in the guinea‐pig gastric antrum, and that both inhibited I Ba in an independent manner.British Journal of Pharmacology (2005) 146 , 129–138. doi: 10.1038/sj.bjp.0706295