Voltage-gated K+ currents regulate resting membrane potential and [Ca2+]i in pulmonary arterial myocytes.
The membrane potential (Em) of pulmonary arterial smooth muscle cells (PASMCs) regulates pulmonary arterial tone by controlling voltage-gated Ca2+ channel activity, which is a major contributor to [Ca2+]i. The resting membrane is mainly permeable to K+; thus, the resting Em is controlled by K+ permeability through sarcolemmal K+ channels. At least three K+ currents, voltage-gated K+ (KV) currents, Ca(2+)-activated K+ (KCa) currents, and ATP-sensitive (KATP) currents, have been identified in PASMCs. In this study, both patch-clamp and quantitative fluorescent microscopy techniques were used to determine which kind(s) of K+ channels (KV, KCa, and/or KATP) is responsible for controlling Em and [Ca2+]i under resting conditions in rat PASMCs. When the bath solution contained 1.8 mmol/L Ca2+ and the pipette solution included 0.1 mmol/L EGTA, depolarizations (-40 to +80 mV) elicited both KCa and KV currents. Removal of extracellular Ca2+ and increase of intracellular EGTA concentration (to 10 mmol/L) eliminated the Ca2+ influx-dependent KCa current. 4-Aminopyridine (4-AP, 5 to 10 mmol/L) but not charybdotoxin (ChTX, 10 to 20 nmol/L) significantly reduced KV current under these conditions. In current-clamp experiments, 4-AP decreased Em (depolarization) and induced Ca(2+)-dependent action potentials; this depolarization increased [Ca2+]i in intact PASMCs. Neither ChTX nor the specific blocker of KATP channels, glibenclamide (2 to 10 mumol/L), caused membrane depolarization and the increase in [Ca2+]i. However, pretreatment of PASMCs with ChTX enhanced the 4-AP-induced increase in [Ca2+]i.(ABSTRACT TRUNCATED AT 250 WORDS)
Yuan
X J
XJ
Department of Medicine, University of Maryland School of Medicine, Baltimore 21201, USA.
D000255:Adenosine Triphosphate / Q000378:metabolism; D000704:Analysis of Variance; D000818:Animals; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000378:metabolism / Q000502:physiology*; D002478:Cells, Cultured; D018999:Charybdotoxin; D004594:Electrophysiology; D005905:Glyburide / Q000494:pharmacology; D015640:Ion Channel Gating; D008564:Membrane Potentials / Q000502:physiology; D008954:Models, Biological; D009131:Muscle, Smooth, Vascular / Q000166:cytology* / Q000378:metabolism / Q000502:physiology; D015221:Potassium Channels / Q000378:metabolism / Q000502:physiology*; D011651:Pulmonary Artery / Q000166:cytology / Q000378:metabolism / Q000502:physiology*; D051381:Rats; D012508:Sarcolemma / Q000378:metabolism; D012604:Scorpion Venoms / Q000494:pharmacology
D015220:Calcium Channels; D015221:Potassium Channels; D012604:Scorpion Venoms; D018999:Charybdotoxin; D000255:Adenosine Triphosphate; D005905:Glyburide; D002118:Calcium