Oxygen Sensitivity of Cloned Voltage-Gated K ⁺ Channels Expressed in the Pulmonary Vasculature

Abstract

Abstract-Hypoxic pulmonary vasoconstriction is initiated by inhibiting one or more voltage-gated potassium (Kv) channel in the vascular smooth muscle cells (VSMCs) of the small pulmonary resistance vessels. Although progress has been made in identifying which Kv channel proteins are expressed in pulmonary arterial (PA) VSMCs, there are conflicting reports regarding which channels contribute to the native O 2 -sensitive K ϩ current. In this study, we examined the effects of hypoxia on the Kv1.2, Kv1.5, Kv2.1, and Kv9.3 ␣ subunits expressed in mouse L cells using the whole-cell patch-clamp technique. Hypoxia (PO 2 ϭϷ30 mm Hg) reversibly inhibited Kv1.2 and Kv2.1 currents only at potentials more positive than 30 mV. In contrast, hypoxia did not alter Kv1.5 current. Currents generated by coexpression of Kv2.1 with Kv9.3 ␣ subunits were reversibly inhibited by hypoxia in the voltage range of the resting membrane potential (E M ) of PA VSMCs (Ϸ28% at Ϫ40 mV). Coexpression of Kv1.2 and Kv1.5 ␣ subunits produced currents that displayed kinetic and pharmacological properties distinct from Kv1.2 and Kv1.5 channels expressed alone. Moreover, hypoxia reversibly inhibited Kv1.2/Kv1.5 current activated at physiologically relevant membrane potentials (Ϸ65% at Ϫ40 mV). These results indicate that (1) hypoxia reversibly inhibits Kv1.2 and Kv2.1 but not Kv1.5 homomeric channels, (2) Kv1.2 and 1.5 ␣ subunits can assemble to form an O 2 -sensitive heteromeric channel, and (3) Key Words: Kv channel Ⅲ hypoxia Ⅲ pulmonary artery Ⅲ heteromeric H ypoxia induces constriction of the small pulmonary resistance arteries, a process known as hypoxic pulmonary vasoconstriction (HPV). 1 This constrictor response is the opposite of that which occurs in resistance vessels of the systemic circulation. In these vessels, hypoxia results in vasodilation. 2 In the fetus, HPV contributes to high pulmonary arterial resistance by diverting blood flow through the ductus arteriosus. 3 In the adult, HPV reduces blood flow through atelectatic or underventilated areas of the lung where ventilation is not adequate for oxygenation. 3 In this way, short-term HPV is an essential mechanism that helps match ventilation to perfusion, diverting blood flow away from poorly ventilated regions of the lung to maximize arterial saturation. 4 However, when hypoxia becomes more generalized, as seen in patients suffering from either long-term obstructive lung diseases or high altitude exposure, 4,5 the subsequent pulmonary vasoconstriction causes an increase in pulmonary arterial pressure that can lead to the development of pulmonary hypertension.In pulmonary arterial (PA) vascular smooth muscle cells (VSMCs), voltage-gated potassium (Kv) channels play an important role in setting the resting membrane potential (E M ϭϷϪ55 mV) and, consequently, vascular tone. 6 -8 It is thought that hypoxia reversibly inhibits Kv channels and, thereby, regulates vasoconstriction. 7,9 -12 This hypothesis is supported by the observation that hypoxia inhibits whole-cell K ϩ currents and ca...

Localization-dependent activity of the Kv2.1 delayed-rectifier K + channel

“…One interesting area for future research will be to examine the effect of apoptotic stimuli on Kv2.1 activation because this channel is essential for this oxidant-induced cell death (11,25). Additional declustering stimuli will include N 2 saturated solutions as a means of establishing hypoxia (26). Ultimately, these declustering experiments will have to be performed in hippocampal neurons, preferably in a brain slice preparation.…”

“…Details with respect to these methods are contained within SI Text and corresponding references (13,14,26,(32)(33)(34)(35)(36). Only low passage number (<45) HEK cells lacking endogenous K + channel activity were used.…”

Viral Gene Transfer of Dominant-Negative Kv4 Construct Suppresses an O2-Sensitive K+Current in Chemoreceptor Cells

“…However, determination of the molecular constituents of the O 2 -sensitive K ϩ currents in native tissues is a relevant issue, not only to understand the molecular mechanisms of O 2 detection in hypoxia-sensitive tissues, but also to provide a physiological meaning to the reported O 2 modulation of cloned channels expressed in heterologous systems (Patel et al, 1997;Fearon et al, 1999;Hulme et al, 1999;Pérez-García et al, 1999).…”

“…Molecular biology techniques have identified several K ϩ channel genes expressed in some of the hypoxiasensitive tissues, and for some of them low pO 2 modulation has been studied in heterologous expression systems (Patel et al, 1997;Yuan et al, 1998;O'Kelly et al, 1999). However, there are conflicting reports with respect to which of these channels contributes to the native O 2 -sensitive K ϩ channels, because different genes can produce channels with similar phenotypic properties (Patel et al, 1997;Hulme et al, 1999).…”

SUMO modification regulates inactivation of the voltage-gated potassium channel Kv1.5

“…Electrophysiological recordings and analysis were conducted as previously described (51). The current-voltage relationships and activation curves were measured by using 250-ms voltage-clamp pulses applied in 10-mV steps between Ϫ80 mV and ϩ60 mV.…”