Neural M-type (KCNQ/K_v7) K⁺ channels control somatic excitability, bursting and neurotransmitter release throughout the nervous system. Their activity is regulated by multiple signaling pathways triggered via stimulation of numerous receptors. One pathway involves depletion of phosphatidylinositol 4,5-bisphosphate (PIP₂) in the membrane, whose interaction with the channels is thought necessary for their function. Another pathway requires IP₃-mediated intracellular Ca²⁺ (Ca²⁺_i) signals and calmodulin action. We seek to localize the sub-domains on the channels critical to their differential affinity for PIP₂, and the mechanisms of receptor-specific modulation of M-type channels via these two intracellular pathways. cDNA clones for wild-type and mutant K_v7 channels were expressed in mammalian CHO cells and studied via single-channel patch or perforated-patch voltage clamp. Recordings from chimeras between high-PIP₂ affinity K_v7.3 and low-PIP₂ affinity K_v7.4 channels indicate the linker between the 1^st and 2^nd homologous domains in the carboxy-terminus determines PIP₂ affinity, and is a possible binding site. Point mutants within this linker in K_v7.2 and K _v7.3 further localize the critical region to a cluster of basic residues. In superior cervical ganglion sympathetic neurons, muscarinic M₁, angiotensin II AT₁, bradykinin B₂ and purinergic P2Y agonists suppress M current (I_M). In these neurons, stimulation of B₂ and P2Y, but not M₁ nor AT₁, receptors induce Ca²⁺_i signals. Expression of IP₃ scavengers or IP₃ phosphatases, and wild-type or dominant-negative calmodulin, shows bradykinin and purinergic, but not muscarinic nor angiotensin, suppression of I_M to require IP₃ accumulation and Ca²⁺_i signals in concert with calmodulin. We group these receptors into two fundamental modes of action.

Supported by NIH grant RO1 NS043394