Ca2+-dependent K+ channel

The H2 receptor is the second class of HA receptors. This is another G-protein-coupled receptor but, unlike the Hi receptor, the H2 receptor is coupled to adenylyl cyclase via the GTP-binding Gs protein (Hill et ah, 1997). Encoded by an intronless gene and located on human chromosome 5, the H2 receptor is made up of c. 358 amino acids (Gantz et ah, 1991 Traiffort et ah, 1995). Activation of the H2 receptor causes an accumulation of cAMP and activation of protein kinase A that eventually leads to the activation of cyclic-AMP-response element (CRE)-binding protein (CREB) (Hill et ah, 1997). In neurons, the H2 receptor mediates its excitatory effects by blocking the Ca2+-dependent K+ channel (Haas Konnerth, 1983). 

Vaca, L., Schilling, W. P., and Kunze, D. L. 1992. G-protein-mediated regulation of a Ca2+-dependent K+ channel in cultured vascular endothelial cells. Pflugers Arch. 422 66-74. 

Takahashi A, Ikehara T, Hosokawa K, et al. 1995. Properties of Ca2+-dependent K+ channels of human gingival fibroblasts. J Dent Res 74(8) 1507-1512. 

While some K+ channels are voltage-gated, others are modulated by G proteins (that are in turn regulated by particular hormones such as dopamine or adenosine) (see Chapter 5) and others are subject to Ca2+-dependent activation. A Ca2+-dependent K+ channel is opened by the lignan nordihydroguaiaretic acid (NDGA). 

CA, carbonic anhydrase Ca2+ CH, Ca2+ channel Ca2+, -CaM, Ca2+, -calmodulin complex Ca2+-K+ CH, Ca2+-dependent K+ channel CAB Pase, cyclic AMP-binding phosphatase CABNase, cyclic nucleotide-binding nucleotidase... 

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