potassium large conductance pH-sensitive channel, subfamily M, alpha member 3 Synonyms: Slo3 kcnu1 Slo3 Kcnma3 KCa5. Symbol: Kcnma3
The mouse Slo3 gene (KCNMA3) encodes a K+ channel that is regulated by changes in cytosolic pH. Like Slo1 subunits responsible for the Ca2+ and voltage-activated BK-type channel, the Slo3 α subunit contains a pore module
with homology to voltage-gated K+ channels and also an extensive cytosolic C terminus thought to be responsible
for ligand dependence. For the Slo3 K+ channel, increases in cytosolic pH promote channel activation, but very little is known about many fundamental properties of Slo3 currents. (Zhang )
Slo3 shares the most extensive sequence homology with Slo1 (Schreiber 1998 ).
Kcnma3 : potassium large conductance pH-sensitive channel, subfamily M, alpha member 3
In contrast to Slo1, Slo3 is insensitive to cytosolic Ca2+ and appears sensitive to cytosolic pH (Schreiber et al., 1998 ; Xia et al., 2004 ).
K+ channels formed from α subunits encoded by the Slo
gene family (Adelman et al., 1992 ; Butler et al., 1993 )
are characterized by a large cytosolic C-terminal structure that is thought to be involved in ligand-dependent
regulation of the channels (Wei et al., 1994 ; Schreiber
and Salkoff , 1997; Schreiber et al. , 1998 ; Bhattacharjee
et al., 2002 ; Jiang et al., 2002 ; Shi et al., 2002 ; Xia
et al., 2002 ; Bhattacharjee et al., 2003 ; Yuan et al., 2003 ;
Xia et al., 2004 ). In fact, the hallmark for each member of the Slo family appears to be regulation by a specific cytosolic ligand: pH
for Slo3 (Schreiber et al., 1998 ; Xia et al., 2004 ).
to the wide distribution of channels arising from either
Slo1 and Slo2.x subunits, Slo3 has a much more limited
pattern of expression than the other family members,
being found predominantly in mouse testis (Schreiber
et al., 1998 ).
Slo1 and Slo3 differ
in two primary ways: first, the intrinsic voltage dependence of the Slo3 closed–open equilibrium is weaker,
and, second, voltage sensor movement in Slo3 is much
more weakly coupled to channel opening. Both
activation and deactivation are best described by two exponential components, both of which are only weakly voltage dependent. Qualitatively, the properties of the two kinetic components in the activation time course suggest
that increases in pH increase the fraction of more rapidly opening channels.