Heteromultimeric Kv1 Channels Contribute to Myogenic Control of Arterial Diameter

Abstract

Abstract-Inhibition of vascular smooth muscle (VSM) delayed rectifier K ϩ channels (K DR ) by 4-aminopyridine (4-AP; 200 mol/L) or correolide (1 mol/L), a selective inhibitor of Kv1 channels, enhanced myogenic contraction of rat mesenteric arteries (RMAs) in response to increases in intraluminal pressure. The molecular identity of K DR of RMA myocytes was characterized using RT-PCR, real-time PCR, and immunocytochemistry. Transcripts encoding the pore-forming Kv␣ subunits, Kv1.2, Kv1.4, Kv1.5, and Kv1.6, were identified and confirmed at the protein level with subunit-specific antibodies. Kv␤ transcript (␤1.1, ␤1.2, ␤1.3, and ␤2.1) expression was also identified. Kv1.5 message was Ϸ2-fold more abundant than that for Kv1.2 and Kv1.6. Transcripts encoding these three Kv1␣ subunits were Ϸ2-fold more abundant in 1st/2nd order conduit compared with 4th order resistance RMAs, and Kv␤1 was 8-fold higher than Kv␤2 message. RMA K DR activated positive to Ϫ50 mV, exhibited incomplete inactivation, and were inhibited by 4-AP and correolide. However, neither ␣-dendrotoxin or -dendrotoxin affected RMA K DR , implicating the presence of Kv1.5 in all channels and the absence of Kv1.1, respectively. Currents mediated by channels because of coexpression of Kv1.2, Kv1.5, Kv1.6, and Kv␤1.2 in human embryonic kidney 293 cells had biophysical and pharmacological properties similar to those of RMA K DR . It is concluded that K DR channels composed of heteromultimers of Kv1 subunits play a critical role in myogenic control of arterial diameter. Key Words: delayed rectifier potassium channel Ⅲ KCNA Ⅲ vascular smooth muscle Ⅲ myogenic contraction Ⅲ arterial diameter T he ability of small resistance arteries to develop myogenic tone in response to elevations in intraluminal (or transmural) pressure is an essential autoregulatory mechanism and an important determinant of peripheral vascular resistance, regional blood flow, and blood pressure. Pressureinduced depolarization of vascular smooth muscle (VSM) leading to increased intracellular Ca 2ϩ ([Ca 2ϩ ] i ) via voltagedependent activation of Ca 2ϩ channels is required for myogenic tone development. 1,2 However, the depolarization does not evoke regenerative action potentials, rather incremental changes in diameter are achieved by graded, steady-state depolarizations. 3 Our understanding of the ionic basis of this precise control of myogenic depolarization is incomplete.Increased intraluminal pressure is thought to activate nonselective cation or Cl Ϫ channels of VSM cells, 2 with the level of depolarization attributable to these channels precisely controlled by an activation of VSM K ϩ channels. 3 Compelling evidence for a contribution of large Ca 2ϩ -activated K ϩ channels (BK Ca ) to this feedback control comes from studies using specific inhibitors (eg, iberiotoxin) and transgenic mice lacking the BK Ca modulatory ␤1 subunit. 4 However, whether other channels are also involved in controlling myogenic depolarization in VSM is not clear.Voltage-gated delayed rectifier channels (K DR ) ...

Heterogeneous Kv1 function and expression in coronary myocytes from right and left ventricles in rats

“…Recently, it has been shown that heteromultimeric Kv1 channels contributed to myogenic control of arterial diameters in rats (27). Moreover, in rat renal microvasculature, K ϩ current was thought to be heteromultimeric delayed-rectifier Kv1.2 and A-type Kv1.4 subunits that contribute to blood pressure regulation (12), whereas Kv1.2/Kv1.5 heteromultimeric channel was preferentially expressed in rat cerebral myocytes and contribute to E m and diameter of small cerebral arteries (1).…”

Use of Patch Clamp Electrophysiology to Identify Off-Target Effects of Clinically Used Drugs

“…These can be used to eliminate a subtype of K + current or determine the contribution of that subtype to the larger mix of K + currents. It is important to consider that different members within a subfamily of K + channels can combine to form functional heteromeric channels, which may vary in their sensitivities to toxins depending on the subunit composition (Tytgat et al, 1995;Plane et al, 2005) In some cases, a combination of pharmacological approaches and voltage protocols that take advantage of the unique biophysical properties of the K + channels expressed in the cell type under investigation can effectively isolate a specific subtype of K + conductance (see example below).…”

Mechanisms of myogenic response: Ca2+-dependent and -independent signaling

“…Kv1 (Shaker) channels produce the physiologically relevant Kv current, which regulates arterial myocyte membrane potential and tone of systemic resistance arteries (Plane et al, 2005). Kv2 (Shab) channel expression in aortic (Tammaro et al, 2004.…”