Modulation of voltage-dependent Ba2+ currents in the guinea-pig gastric antrum by cyclic nucleotide-dependent pathways.
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 mM), a membrane-permeable ester of cAMP, and isoproterenol, a selective beta-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 mM) and 8-Br-cGMP (0.1-1 mM) 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.
Zhu
Hai-Lei
HL
Department of Pharmacology, Graduate School of Medical Sciences, Kyushu University, Higashi Ward, Fukuoka, Japan.
Hirst
G David S
GD
Ito
Yushi
Y
Teramoto
Noriyoshi
N
D000818:Animals; D001464:Barium / Q000494:pharmacology; D003994:Bucladesine / Q000494:pharmacology*; D020746:Calcium Channels, L-Type / Q000187:drug effects* / Q000502:physiology; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000031:analogs & derivatives / Q000494:pharmacology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000502:physiology; D006152:Cyclic GMP / Q000031:analogs & derivatives* / Q000494:pharmacology; D017869:Cyclic GMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000502:physiology; D005260:Female; D006168:Guinea Pigs; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects*; D032389:Myocytes, Smooth Muscle / Q000187:drug effects* / Q000502:physiology; D010455:Peptides / Q000494:pharmacology; D011706:Pyloric Antrum / Q000187:drug effects / Q000502:physiology; D013873:Thionucleotides / Q000494:pharmacology
D020746:Calcium Channels, L-Type; D010455:Peptides; D013873:Thionucleotides; C061479:protein kinase inhibitor peptide; D005576:Colforsin; C016957:adenosine-3',5'-cyclic phosphorothioate; D001464:Barium; C016276:8-bromocyclic GMP; D003994:Bucladesine; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D017869:Cyclic GMP-Dependent Protein Kinases; D006152:Cyclic GMP; D007545:Isoproterenol