Ion channels control the electrical properties of neurons and other excitable cell types by selectively allowing ion to flow through the plasma membrane. To regulate neuronal excitability, the biophysical properties of ion channels are modified by signaling proteins and molecules, which often bind to the channels themselves to form a heteromeric channel complex. Traditional assays examining the interaction between channels and regulatory proteins generally provide little information on the time-course of interactions in living cells. We have now used a novel label-free technology to detect changes in the distribution of mass close to the plasma membrane following modulation of potassium channels by G protein-coupled receptors (GPCRs). This technology uses optical sensors embedded in microplates to detect changes in the refractive index at the surface of cells. Although the activation of GPCRs has been studied with this system, protein-protein interactions due to modulation of ion channels have not yet been characterized. Here we present data that the characteristic pattern of mass distribution following GPCR activation is significantly modified by the presence of a sodium-activated potassium channel, Slack-B, a channel that is known to be potently modulated by activation of these receptors.