[Heterotrimeric G proteins and ion channels].

Direct G protein regulation of ion channels is one of the major mechanisms of the functional regulation of excitable cells by hormones and neurotransmitters. Recent extensive studies indicate that a number of channels are directly regulated by G proteins. In this short review, we focus on the molecular mechanism underlying G protein (GK) regulation fo cardiac muscarinic K+ channels. This channel was reported to be activated in the inside-out configuration by both exogenously applied alpha- and beta gamma-subunits of pertussis toxin-sensitive G proteins. There has been a longstanding controversy as to which of the subunits physiologically mediate the effect of GK on this channel. We have established the notion that GK physiologically activates cardiac muscarinic K+ channels through its beta gamma-subunit but not its alpha-subunit.