Voltage-Gated K ⁺ Currents Regulate Resting Membrane Potential and [Ca ²⁺ ] _i in Pulmonary Arterial Myocytes

Abstract

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)

Dehydroepiandrosterone (DHEA) prevents and reverses chronic hypoxic pulmonary hypertension

“…At the cellular level, data clearly indicate that PAHT is associated with an increase in [Ca 2ϩ ] i secondary to membrane depolarization of the PA myocytes (21). This leads to a deep change in the PA properties, and PA from CH rats do not respond to further acute hypoxic stress.…”

NO hyperpolarizes pulmonary artery smooth muscle cells and decreases the intracellular Ca2+ concentration by activating voltage-gated K+ channels.

“…They apparently involve an increase of intracellular cGMP (10,11) as well as membrane hyperpolarization (12,13). The activity of sarcolemmal voltagegated K+ (Kv) channels controls the resting membrane potential (Em), which is, in tum, an important regulator of the intracellular free Ca>2 concentration ([Ca2+1]) (14,15). Changes in [Ca2+]i in pulmonary arterial smooth muscle cells (PASMC) play a critical role in regulating pulmonary vasomotor tone.…”

“…In PASMC, inhibition of Kv channels, for example by 4-aminopyridine (4-AP) (15,16,17), causes membrane depolarization. The depolarization opens voltage-gated Ca2+ channels and thereby initiates Ca2+-dependent action potentials and raises [Ca2+], (15 MATERIALS AND METHODS Cell Preparation.…”

“…The depolarization opens voltage-gated Ca2+ channels and thereby initiates Ca2+-dependent action potentials and raises [Ca2+], (15 MATERIALS AND METHODS Cell Preparation. Rat PASMC primary cultured for 3-7 days were used for this study.…”

“…The PA smooth muscle was then digested with 1.5 mg/ml collagenase, 0.5 mg/ml elastase (Sigma), and 1 mg/ml bovine albumin (Sigma) at 37°C to create a suspension of single PASMC. The cells were resuspended and plated onto 25- (15,27 (20 ,ul) was added to 20 ml of superfusate just before use to make a final NO concentration of 3 ,uM. The half-life of NO (1 ,uM) in normoxic PSS is 500 sec (7).…”