title: Regulation of smooth muscle delayed rectifier K+ channels by protein kinase A.
abstract: We identified voltage-activated K+ channels in freshly dispersed smooth muscle cells from the circular layer of the canine colon in patch-clamp experiments using 200 nM charybdotoxin to suppress 270-pS Ca2+-activated K+ channels (BK channels). Three channel types were distinguished in symmetrical 140 mM KCl solutions: 19.5 +/- 1.7 pS channels (KDR1), 90.6 +/- 5.4 pS channels (KDR2) and 149 +/- 4 pS intermediate-conductance Ca2+-activated K+ channels (IK channels). All three types showed an increase in open probability with membrane depolarization. Ensemble average current from KDR1 channels inactivated with a time constant of 1.7 +/- 0.1 s at +60 mV test potential, while KDR2 and IK channels did not show inactivation. IK channels were activated by free cytoplasmic [Ca2+] (10(-6 )M) but were insensitive to 4-aminopyridine (4-AP, 10 mM) and intracellular tetraethylammonium (TEA, 1 mM). KDR1 channels were sensitive to 4-AP (10 mM) and intracellular TEA (1-10 mM) but not to Ca2+. KDR2 channels did not have a consistent pharmacological profile, suggesting that this class may be comprised of several subtypes. At +40 mV membrane potential, the catalytic subunit of protein kinase A (PKA) increased the open probability of KDR1 channels 3.4-fold and of KDR2 channels 3.9-fold, but had no effect on IK channels. In the absence of Mg-ATP, PKA did not affect channel open probabilities. At physiological membrane potentials (-60 mV) only openings of KDR1 channels could be induced by PKA, suggesting that these 4-AP-sensitive 20-pS K+ channels are primarily responsible for the cAMP-mediated hyperpolarization of colonic smooth muscle cells.
authors.affiliation: Dept. of Physiology, School of Medicine, Hanyang University, Seoul, Korea.
authors.forename: S D
authors.initials: SD
authors.lastname: Koh
authors.forename: K M
authors.initials: KM
authors.lastname: Sanders
authors.forename: A
authors.initials: A
authors.lastname: Carl
mesh_terms: D015761:4-Aminopyridine / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000502:physiology; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D018999:Charybdotoxin / Q000494:pharmacology; D003106:Colon / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000502:physiology*; D004285:Dogs; D005260:Female; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*; D013757:Tetraethylammonium Compounds / Q000494:pharmacology
chemical_list: D015221:Potassium Channels; D013757:Tetraethylammonium Compounds; D018999:Charybdotoxin; D000255:Adenosine Triphosphate; D015761:4-Aminopyridine; D017868:Cyclic AMP-Dependent Protein Kinases; D002118:Calcium