Angiotensin II type 1 receptor-mediated inhibition of K+ channel subunit Kv2.2 in brain stem and hypothalamic neurons

Angiotensin II (Ang II) has powerful modulatory actions on cardiovascular f unction that are mediated by specific receptors located on neurons within t he hypothalamus and brain stem. Incubation of neuronal cocultures of rat hy pothalamus and brain stem with Ang II elicits an Ang II type 1 (AT(1)) rece ptor-mediated inhibition of total outward K+ current that contributes to an increase in neuronal firing rate. However, the exact K+ conductance(s) tha t is inhibited by Ang II are not established. Pharmacological manipulation of total neuronal outward K+ current revealed a component of K+ current sen sitive to quinine, tetraethylammonium, and 4-aminopyridine, with IC50 value s of 21.7 mu mol/L, 1.49 mmol/L, and 890 mu mol/L, respectively, and insens itive to alpha-dendrotoxin (100 to 500 nmol/L), charybdotoxin (100 to 500 n mol/L), and mast cell degranulating peptide (1 mu mol/L). Collectively, the se data suggest the presence of Kv2.2 and Kv3.1b. Biophysical examination o f the quinine-sensitive neuronal K+ current demonstrated a macroscopic cond uctance with similar biophysical properties to those of Kv2.2 and Kv3.1b, A ng II (100 nmol/L), in the presence of the AT(2) receptor blocker PD123,319 , elicited an inhibition of neuronal K+ current that was abolished by quini ne (50 mu mol/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. Coe xpression of Kv2.2 and the AT(1) receptor in Xenopus oocytes demonstrated a n Ang II-induced inhibition of Kv2.2 current, Therefore, these data suggest that inhibition of Kv2.2 contributes to the AT(1) receptor-mediated reduct ion of neuronal K+ current and subsequently to the modulation of cardiovasc ular function.