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ABSTRACT: Resistance pulmonary arteries constrict in response to hypoxia, whereas conduit pulmonary arteries typically do not respond or dilate slightly. One proposed mechanism for this differential response is the variable expression of pulmonary arterial smooth muscle cell voltage-gated K(+) (K(V)) channel subunits (Kv1.2, Kv2.1, Kv1.5, and Kv3.1b) shown to be O(2) sensitive in heterologous expression systems. In this study, immunoblotting and immunohistochemistry were used to examine the expression of K(V) channel alpha- and beta-subunits in the bovine pulmonary arterial circulation to determine whether differential K(V) channel subunit distribution is responsible for the distinct sensitivities of pulmonary arteries to hypoxia. Surprisingly, there was little difference in the expression levels of Kv1.2, Kv1.5, and Kv2.1 between conduit and resistance pulmonary arteries. In contrast, expression of the Kv3.1b alpha-subunit and Kv beta.1, Kv beta 1.2, and Kv beta 1.3 accessory subunits dramatically increased along the pulmonary arterial tree. The differential expression of all the beta-subunits but of only one of the putative O(2)-sensitive alpha-subunits suggests that the alpha-subunits alone are not the O(2) sensors but further implicates the auxiliary beta-subunits in pulmonary arterial O(2) sensing.
AJP Lung Cellular and Molecular Physiology 01/2002; 281(6):L1350-60. · 3.66 Impact Factor
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ABSTRACT: The hypoxia-induced membrane depolarization and subsequent constriction of small resistance pulmonary arteries occurs, in part, via inhibition of vascular smooth muscle cell voltage-gated K+ (KV) channels open at the resting membrane potential. Pulmonary arterial smooth muscle cell KV channel expression, antibody-based dissection of the pulmonary arterial smooth muscle cell K+ current, and the O2 sensitivity of cloned KV channels expressed in heterologous expression systems have all been examined to identify the molecular components of the pulmonary arterial O2-sensitive KV current. Likely components include Kv2.1/Kv9.3 and Kv1.2/Kv1.5 heteromeric channels and the Kv3.1b alpha-subunit. Although the mechanism of KV channel inhibition by hypoxia is unknown, it appears that KV alpha-subunits do not sense O2 directly. Rather, they are most likely inhibited through interaction with an unidentified O2 sensor and/or beta-subunit. This review summarizes the role of KV channels in hypoxic pulmonary vasoconstriction, the recent progress toward the identification of KV channel subunits involved in this response, and the possible mechanisms of KV channel regulation by hypoxia.
AJP Lung Cellular and Molecular Physiology 08/2001; 281(1):L1-12. · 3.66 Impact Factor
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ABSTRACT: Ion channel targeting within neuronal and muscle membranes is an important determinant of electrical excitability. Recent evidence suggests that there exists within the membrane specialized microdomains commonly referred to as lipid rafts. These domains are enriched in cholesterol and sphingolipids and concentrate a number of signal transduction proteins such as nitric-oxide synthase, ligand-gated receptors, and multiple protein kinases. Here, we demonstrate that the voltage-gated K(+) channel Kv2.1, but not Kv4.2, targets to lipid rafts in both heterologous expression systems and rat brain. The Kv2.1 association with lipid rafts does not appear to involve caveolin. Depletion of cellular cholesterol alters the buoyancy of the Kv2.1 associated rafts and shifts the midpoint of Kv2.1 inactivation by nearly 40 mV without affecting peak current density or channel activation. The differential targeting of Kv channels to lipid rafts represents a novel mechanism both for the subcellular sorting of K(+) channels to regions of the membrane rich in signaling complexes and for modulating channel properties via alterations in lipid content.
Journal of Biological Chemistry 04/2000; 275(11):7443-6. · 4.77 Impact Factor
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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(+) current. In this study, we examined the effects of hypoxia on the Kv1.2, Kv1.5, Kv2.1, and Kv9.3 alpha subunits expressed in mouse L cells using the whole-cell patch-clamp technique. Hypoxia (PO(2)= approximately 30 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 alpha subunits were reversibly inhibited by hypoxia in the voltage range of the resting membrane potential (E(M)) of PA VSMCs ( approximately 28% at -40 mV). Coexpression of Kv1.2 and Kv1.5 alpha 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 ( approximately 65% at -40 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 alpha subunits can assemble to form an O(2)-sensitive heteromeric channel, and (3) only Kv1.2/Kv1.5 and Kv2.1/Kv9.3 heteromeric channels are inhibited by hypoxia in the voltage range of the PA VSMC E(M). Thus, these heteromeric channels are strong candidates for the K(+) channel isoforms initiating hypoxic pulmonary vasoconstriction.
Circulation Research 10/1999; 85(6):489-97. · 9.49 Impact Factor
