Angiotensin II Type 1 Receptor–Mediated Inhibition of K ⁺ Channel Subunit Kv2.2 in Brain Stem and Hypothalamic Neurons

Abstract

Angiotensin II (Ang II) has powerful modulatory actions on cardiovascular function that are mediated by specific receptors located on neurons within the hypothalamus and brain stem. Incubation of neuronal cocultures of rat hypothalamus and brain stem with Ang II elicits an Ang II type 1 (AT1) receptor-mediated inhibition of total outward K+ current that contributes to an increase in neuronal firing rate. However, the exact K+ conductance(s) that is inhibited by Ang II are not established. Pharmacological manipulation of total neuronal outward K+ current revealed a component of K+ current sensitive to quinine, tetraethylammonium, and 4-aminopyridine, with IC50 values of 21.7 micromol/L, 1.49 mmol/L, and 890 micromol/L, respectively, and insensitive to alpha-dendrotoxin (100 to 500 nmol/L), charybdotoxin (100 to 500 nmol/L), and mast cell degranulating peptide (1 micromol/L). Collectively, these data suggest the presence of Kv2.2 and Kv3.1b. Biophysical examination of the quinine-sensitive neuronal K+ current demonstrated a macroscopic conductance with similar biophysical properties to those of Kv2.2 and Kv3.1b. Ang II (100 nmol/L), in the presence of the AT2 receptor blocker PD123,319, elicited an inhibition of neuronal K+ current that was abolished by quinine (50 micromol/L). Reverse transcriptase-polymerase chain reaction analysis confirmed the presence of Kv2.2 and Kv3.1b mRNA in these neurons. However, Western blot analyses demonstrated that only Kv2.2 protein was present. Coexpression of Kv2.2 and the AT1 receptor in Xenopus oocytes demonstrated an Ang II-induced inhibition of Kv2.2 current. Therefore, these data suggest that inhibition of Kv2.2 contributes to the AT1 receptor-mediated reduction of neuronal K+ current and subsequently to the modulation of cardiovascular function.

Novel Mechanisms of Sympathetic Regulation in Chronic Heart Failure

“…[57][58][59] This mechanism may be very important in the setting of various disease states that are characterized by sympathoexcitation, such as CHF and hypertension. Data from the laboratory of Sumners and coworkers 60,61 have confirmed this mechanism. Preliminary data from our laboratory indicates that rats with CHF express lower amounts of the KV 4.3 protein in the RVLM than do sham rats.…”

Chronotropic Action of Angiotensin II in Neurons via Protein Kinase C and CaMKII

“…Such influences may take the form of distinct actions on the biophysical properties of the Kv2.2 channel, which mediates the inhibitory effects of Ang II on neuronal I Kv. 24 Thus, PKC and CaMKII may have unique regulatory influences on channel properties such as activation, inactivation, open or closed time, or time to first latency. Once we have a better understanding of the mechanisms by which PKC and CaMKII regulate Kv2.2, we will be able to determine whether there are distinct actions of each kinase on channel activity and ultimately neuronal firing rate.…”

The Kv2.1 C Terminus Can Autonomously Transfer Kv2.1-Like Phosphorylation-Dependent Localization, Voltage-Dependent Gating, and Muscarinic Modulation to Diverse Kv Channels

“…The rabbit polyclonal antibodies used were KC [generated against the distal C-terminal end of Kv2.1 (Trimmer, 1991)], anti-Kv2.1e [generated against the S1-S2 extracellular region of Kv2.1 (Lim et al, 2000)], and Kv1.5e (generated against the S1-S2 extracellular region of Kv1.5). The mouse monoclonal antibodies used were K89/41 [generated against the distal C-terminal domain of Kv2.1 (Antonucci et al, 2001)], K39/25 [generated against the S1-S2 extracellular loop of Kv2.1 (Lim et al, 2000)], and K37/89 [generated against the cytoplasmic N-terminal domain of Kv2.2 (Gelband et al, 1999)]. …”