Angiotensin II regulates neuronal excitability via phosphatidylinositol 4,5‐bisphosphate‐dependent modulation of Kv7 (M‐type) K+channels

Publisher Website
Google Scholar
Abstract
Voltage‐gated Kv7 (KCNQ) channels underlie important K+currents in many different types of cells, including the neuronal M current, which is thought to be modulated by muscarinic stimulation via depletion of membrane phosphatidylinositol 4,5‐bisphosphate (PIP2). We studied the role of modulation by angiotensin II (angioII) of M current in controlling discharge properties of superior cervical ganglion (SCG) sympathetic neurons and the mechanism of action of angioII on cloned Kv7 channels in a heterologous expression system. In SCG neurons, which endogenously express angioII AT1 receptors, application of angioII for 2 min produced an increase in neuronal excitability and a decrease in spike‐frequency adaptation that partially returned to control values after 10 min of angioII exposure. The increase in excitability could be simulated in a computational model by varying only the amount of M current. Using Chinese hamster ovary (CHO) cells expressing cloned Kv7.2 + 7.3 heteromultimers and AT1 receptors studied under perforated patch clamp, angioII induced a strong suppression of the Kv7.2/7.3 current that returned to near baseline within 10 min of stimulation. The suppression was blocked by the phospholipase C inhibitor edelfosine. Under whole‐cell clamp, angioII moderately suppressed the Kv7.2/7.3 current whether or not intracellular Ca2+was clamped or Ca2+stores depleted. Co‐expression of PI(4)5‐kinase in these cells sharply reduced angioII inhibition, but did not augment current amplitudes, whereas co‐expression of a PIP25′‐phosphatase sharply reduced current amplitudes, and also blunted the inhibition. The rebound of the current seen in perforated‐patch recordings was blocked by the PI4‐kinase inhibitor, wortmannin (50 μm), suggesting that PIP2re‐synthesis is required for current recovery. High‐performance liquid chromatographic analysis of anionic phospholipids in CHO cells stably expressing AT1 receptors revealed that PIP2and phosphatidylinositol 4‐phosphate levels are to be strongly depleted after 2 min of stimulation with angioII, with a partial rebound after 10 min. The results of this study establish how angioII modulates M channels, which in turn affects the integrative properties of SCG neurons.