| Popis: |
K+ channels represent a large and diverse group of ion channels that play a fundamental role in controlling cell excitability. These channels regulate hormone release from endocrine cells, modulate the pattern of transmitter release from neurons, and set the level of contraction in arterial smooth muscle cells. At first glance, K+ channels can be subdivided into either voltage-gated K+ (Kv) channels or ligand-gated K+ channels, depending on the stimulus that triggers the conformational change that leads to channel opening. Within the wide family of K+ channels gated by voltage, the Kv channels are activated solely by membrane depolarization, whereas high-conductance Ca2+-activated K+ (BKCa) channels require both membrane depolarization and an increased level of cytosolic free Ca2+ ([Ca2+]i) to activate effectively. The use of molecular biology techniques has greatly extended our current understanding regarding the structure and existence of subfamilies of K+ channels. However, three major questions still are the subject of extensive investigation: (1) What is the molecular composition of the different types of K+ channels expressed in vivo, (2) what is the physiological function of these K+ channels, and (3) is the molecular composition and functional profile of K+ channels altered in pathophysiological states? |
