The ''I'' channel (K_Ca3.1), which has a conductance of 20–80 pS, is expressed mainly in peripheral tissues such as those of the

haematopoietic system The haematopoietic system is the system in the body involved in the creation of the cells of blood. Structure Stem cells Haematopoietic stem cells (HSCs) reside in the medulla of the bone ( bone marrow) and have the unique ability to give rise t ...

, colon,

placenta The placenta is a temporary embryonic and later fetal organ that begins developing from the blastocyst shortly after implantation. It plays critical roles in facilitating nutrient, gas and waste exchange between the physically separate mater ...

lung The lungs are the primary organs of the respiratory system in humans and most other animals, including some snails and a small number of fish. In mammals and most other vertebrates, two lungs are located near the backbone on either side of t ...

and

pancreas The pancreas is an organ of the digestive system and endocrine system of vertebrates. In humans, it is located in the abdomen behind the stomach and functions as a gland. The pancreas is a mixed or heterocrine gland, i.e. it has both an end ...

. The K_Ca3.1 channel in

red blood cell Red blood cells (RBCs), also referred to as red cells, red blood corpuscles (in humans or other animals not having nucleus in red blood cells), haematids, erythroid cells or erythrocytes (from Greek ''erythros'' for "red" and ''kytos'' for "holl ...

s was the first Ca²⁺–sensitive K⁺ channel to be identified and it has been implicated in a wide range of cell functions, including vasodilation of the microvasculature, K⁺ flux across

endothelial cell The endothelium is a single layer of squamous endothelial cells that line the interior surface of blood vessels and lymphatic vessels. The endothelium forms an interface between circulating blood or lymph in the lumen and the rest of the vessel ...

s of

brain A brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as vision. It is the most complex organ in a v ...

capillaries and the phagocytic activity of

neutrophil Neutrophils (also known as neutrocytes or heterophils) are the most abundant type of granulocytes and make up 40% to 70% of all white blood cells in humans. They form an essential part of the innate immune system, with their functions varying in ...

s. K_Ca3.1 is of primary importance in the relationship between K⁺ channels and cell proliferation. In the latter case, a human ''hIKCa1'' gene encodes the channel found in

T cell A T cell is a type of lymphocyte. T cells are one of the important white blood cells of the immune system and play a central role in the adaptive immune response. T cells can be distinguished from other lymphocytes by the presence of a T-cell r ...

s, which is responsible for the hyperpolarization that is required to keep Ca²⁺ flowing into the cell through the ''I''_CRAC channels. In comparison with the large-conductance (BK) channels, K_Ca3.1 is much more sensitive to Ca²⁺ and can thus respond to the global level of Ca²⁺. This high affinity for Ca²⁺ depends upon four resident

calmodulin Calmodulin (CaM) (an abbreviation for calcium-modulated protein) is a multifunctional intermediate calcium-binding messenger protein expressed in all eukaryotic cells. It is an intracellular target of the secondary messenger Ca2+, and the bind ...

molecules tightly bound to the

cytoplasmic In cell biology, the cytoplasm is all of the material within a eukaryotic cell, enclosed by the cell membrane, except for the cell nucleus. The material inside the nucleus and contained within the nuclear membrane is termed the nucleoplasm. Th ...

tails of the four pore-forming α-subunits. Before the channel can open, Ca²⁺ must bind to each of the calmodulins to induce the co-operative conformational change that opens the gate, which explains why this process has a

Hill coefficient In biochemistry and pharmacology, the Hill equation refers to two closely related equations that reflect the binding of ligands to macromolecules, as a function of the ligand concentration. A ligand is "a substance that forms a complex with a bio ...

of 4. This Ca²⁺–induced gating process resembles that which has been described for the small-conductance (SK) channels. The fact that calmodulin is prebound to its effector enables the channels to respond to Ca²⁺ very quickly. The

PtdIns3P Phosphatidylinositol 3-phosphate (PtdIns3''P'') is a phospholipid found in cell membranes that helps to recruit a range of proteins, many of which are involved in protein trafficking, to the membranes. It is the product of both the class II and II ...

signaling cassette may play a role in regulating the activity of K_Ca3.1. If this signaling lipid is hydrolysed by MTMR6, which is one of the myotubularins, there is a decrease in the activity of the Ca²⁺–activated channel.Berridge, M.J. (2014) Cell Signaling Biology;

References

Potassium channels Electrophysiology Integral membrane proteins {{cell-biology-stub