Differential segmental activation of Ca2+ -dependent CI-and K+ channels in pulmonary arterial myocytes.
Differential segmental distribution of electrophysiologically distinct myocytes helps to explain the variability of the pulmonary arteries to vasoactive agents. We have studied whether Ca2+ -dependent CI- (CICa) and K+ (KCa) channels are activated differentially in enzymatically dispersed conduit and resistance myocytes. We measured cytosolic [Ca2+] and the changes of membrane current and potential elicited by spontaneous or agonist-induced Ca2+ oscillations. Conduit arteries contained a heterogeneous cell population with a variable mixture of KCa and CICa conductances. Resistance arteries contained a more homogeneous cell population with predominance of CICa channel activation. The relation between KCa and CICa conductances in a given conduit myocyte determines the size of the V(m)change in response to a rise of cytosolic [Ca2+]. Conduit myocytes tend to hyperpolarize towards the K+ equilibrium potential (approximately - 90 m V). In resistance myocytes, release of Ca2+ from stores activates CI Cachannels and brings Vm to a value close to the chloride equilibrium potential (approximately - 20 or - 30 m V) thus favouring opening of Ca2+ channels and Ca2+ influx. In resistance vessels CICachannels contribute to link agonist-induced Ca2+ release from stores and membrane depolarization, thus permitting protracted vasoconstriction.
Smani
T
T
Departamento de Fisiología Médica y Biofísica and Hospital Universitario Virgen del Rocío, Facultad de Medicina, Universidadde Sevilla, Seville, E-41009, Spain.
Iwabuchi
S
S
López-Barneo
J
J
Ureña
J
J
D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects; D018118:Chloride Channels / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D004553:Electric Conductivity; D004594:Electrophysiology; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000378:metabolism*; D009638:Norepinephrine / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000378:metabolism*; D011651:Pulmonary Artery / Q000378:metabolism*; D011817:Rabbits
D018118:Chloride Channels; D015221:Potassium Channels; D002110:Caffeine; D002118:Calcium; D009638:Norepinephrine