sentences:  Chief among these are modulation of Ca2+ release, modulation of cardiac myocyte contractility, and inhibition of voltage gated K+ channels.The reasons for these effects are not well understood, even though σ1 receptors have been linked circumstantially to a wide variety of signal transduction pathways.Links between σ1 receptors and G-proteins have been suggested such as σ1 receptor antagonists showing GTP-sensitive high-affinity binding; there is also, however, some evidence against a G-protein coupled hypothesis.