Tengholm reflects on new work providing insight into the mechanisms of glucose-stimulated somatostatin secretion from δ-cells.
Heart rate control by the funny current (If) involves both fast, cAMP-dependent, and slow, membrane expression–based mechanisms to adapt to different needs.
Cardiac contractile dysfunction and protein kinase C–mediated myofilament phosphorylation in disease and aging
Cardiac troponin I Ser44 is a downstream target for protein kinase C. The current studies show heightened phosphorylation develops during contractile dysfunction in failing human myocardium and in rat models of pressure overload and aging with contractile dysfunction.
Three-dimensional electron microscopy reveals that myosin II molecules are kept inactive by intramolecular interactions between the heads and the tail that inhibit actin binding, ATPase activity, filament formation, and phosphorylation. This suggests how myosin can be stored in cells with minimal energy consumption.
Glucose stimulates somatostatin secretion in pancreatic δ-cells by cAMP-dependent intracellular Ca2+ release
The regulation of somatostatin secretion from islet δ-cells remains obscure. Denwood et al. show that glucose stimulates somatostatin secretion through effects on both δ-cell electrical activity and cAMP-dependent intracellular Ca2+ release.
Ion channels are often found in dense clusters within the plasma membranes of excitable cells. Based on experimental measurements of a wide range of channels in various cell types, Sato et al. propose that channel clusters form stochastically and that their size is regulated by a common feedback mechanism.
Triple arginines as molecular determinants for pentameric assembly of the intracellular domain of 5-HT3A receptors
Serotonin type 3A receptors are homopentameric ligand-gated ion channels that are thought to assemble via interactions involving the subunits’ extracellular and transmembrane domains. Pandhare et al. reveal that channel assembly is also determined by three arginine residues in the receptor’s intracellular domain.
Methods and Approaches
Many cellular processes depend on the movement of ions across membranes, but current electrophysiological methods can only measure movements that generate an electrical current. Heiny et al. describe a new method to measure dynamic changes of intracellular ion concentration resulting from either electroneutral or electrogenic ion fluxes under voltage or current clamp.