Penetrating at least one phospholipid bilayer of a membrane. May also refer to the state of being buried in the bilayer with no exposure outside the bilayer. When used to describe a protein, indicates that all or part of the peptide sequence is embedded in the membrane.
Double layer of lipid molecules that encloses all cells, and, in eukaryotes, many organelles; may be a single or double lipid bilayer; also includes associated proteins.
Tricyclic antidepressants (TCAs) influence the astroglial Kir4.1
channels expressed in HEK293T cells. Su et al. 
demonstrated that nortriptyline and other
TCAs, including amitriptyline, desipramine, and imipramine, inhibit homomeric Kir4.1 channels in a voltage- and
Unlike other Kir family
members, heteromultimerization of inter-subfamily members
Kir4.1 and Kir5.1 leads to a channel with distinct functional
properties (Casamassima, Konstas , Pessia , Tanemoto , Tucker , Xu , Yang ). Of particular interest in these newly emerging
properties is the enhanced sensitivity to intracellular pH (pKa
7.45), allowing the heteromeric Kir4.1–Kir5.1 channel to detect
pH changes at physiological levels (Pessia , Xu , Yang , Xui ).
Kir4.1 alone exists at the end-feet of retinal Mueller cells, and both
Kir4.1 and Kir5.1, are detected in the cell body (Ishii ).
It was shown that, among them, Kir4.1 and Kir5.1 are
expressed predominantly in brain astrocytes and retinal
Muller cells (Takumi et al., 1995 ; Ishii et al., 1997 , 2003;
Poopalasundaram et al., 2000 ; Hibino et al., 2004 ).
The Kir4.1 and Kir5.1 subunits are expressed in the proximal
convoluted tubule, the distal convoluted tubule and the cortical
collecting duct of the kidney (Tucker , Tanemoto , Tanemoto ).
Kir channels are either homotetramers of Kir4.1 or heterotetramers of Kir4.1 and Kir5.1, both of which constitutively
allow large inward K+ currents at potentials negative to EK
and small, but significant, outward K+ currents at those
positive to EK (Takumi et al., 1995 ; Ishii et al., 1997 ;
Tanemoto et al., 2000 ; Higashi et al., 2001 ). Thus, depending
on the difference between local EK and the membrane potential of astrocytes, these Kir channels can mediate either
absorption or extrusion of K+ across the astroglial cell membrane and thus can act as the spatial K+-buffering current. (Su )
In addition, Kir4.1 channel and the water channel, aquaporin-4, are colocalized in certain membrane domains of
brain astrocytes and Muller cells, suggesting that spatial K+ buffering may couple with water movement across the astroglial membrane (Nagelhus et al., 1999 ; Amiry-Moghaddam et
al., 2003 ; Puwarawuttipanit et al., 2006 ).
Kir4.1 and Kir5.1 subunits are expressed in the
kidney, eye and brainstem suggests that the channel may be a candidate molecule for the regulation of K+ homeostasis and
central CO2 chemoreception (Pessia , Yang , Jiang , Wu ).