Identification, cloning and expression of rabbit vascular smooth muscle Kv1.5 and comparison with native delayed rectifier K⁺ current

Abstract

Vascular smooth muscle K¤ channels play a critical role in the control of arterial tone and blood pressure by contributing to resting membrane potential and, thereby, to the regulation of L-type Ca¥ channel activation, Ca¥ influx and contraction. Several types of K¤ channels, including large conductance Ca¥-activated (BKCa), ATP-sensitive, inward rectifier, and voltage-gated, delayed rectifier (KDR) channels are believed to contribute to membrane K¤ conductance depending on the vascular bed, physiological condition and presence of vasoactive agonists (Nelson & Quayle, 1995). Rapidly activating and slowly inactivating KDR channels have been the focus of several recent studies and it is now recognized that these channels participate in (i) control of myogenic tone in resistance vasculature (Knot & Nelson, 1995), (ii) the vasodilatory and constrictor responses of some vessels to vasoactive agonists (Satake et al. 1996;Dong et al. 1998), and (iii) the response of vascular myocytes to the activation of serineÏthreonine kinases, e.g. cAMPdependent protein kinase (PKA) and protein kinase C (PKC) (

Molecular Composition of 4-Aminopyridine-Sensitive Voltage-Gated K + Channels of Vascular Smooth Muscle

“…4,5,8,9,11,24 This level of 4-AP sensitivity and the biophysical properties of the currents are consistent with those previously identified for Kv1-containing, 11,17,[22][23][24][25][26] but not Kv2-to 4-containing, 26 -31 Kv channels. The properties of whole-cell and unitary currents due to expression of Kv1.5 cloned from RPV closely mimicked those of native RPV K DR channels.…”

“…[1][2][3][4][5][6]11,24 We attribute the K TO component to the expression of Kv1.4, but it is unlikely that this subunit contributes substantially to the K DR current. Whole-cell currents, as a result of the expression of Kv1.4 in heterologous cell types, 25,40 exhibit several characteristics consistent with those of vascular K TO currents.…”

“…Kv1.2 and Kv1.5 are the only Kv1␣ subunits expressed in RPV that display delayed activation and slow inactivation. 11,17,[22][23][24][25]36 The dominant component of Kv current in RPV myocytes exhibits half-maximal activation at ϷϪ15 mV and inactivates over a slow time course that occurs with time constants of Ϸ0.5 and 3 seconds. 2 20,21 but our finding of Kv␤ subunit protein expression and coassembly with Kv1␣ subunits is novel for vascular smooth muscle.…”

“…11 In this study, we demonstrate immunolabeling of myocytes with antibodies to Kv1.2, Kv1.4, and the Kv␤1. circresaha.org).…”

“…The properties of whole-cell and unitary currents due to expression of Kv1.5 cloned from RPV closely mimicked those of native RPV K DR channels. 11 However, homomultimeric Kv1.5 channels do not share functional identity with vascular K DR because (1) differences in rate and voltage dependence of inactivation are apparent 11 ; (2) RPV Kv1.5 channels in inside-out membrane patches of mouse L cells or human embryonic kidney 293 (HEK) cells do not exhibit modulation by purified protein kinase A in the presence of ATP 32 ; and (3) 4-AP treatment is associated with a positive shift in the voltage dependence of activation of native K DR , but not Kv1.5 channels, as described in another study published in this issue of Circulation Research by Kerr et al 24 This lack of functional identity indicates that Kv1.5 cannot be the only Kv1 subunit contributing to K DR channels of vascular myocytes.…”