Role of CaCMKII in the cross talk between ionotropic nucleotide and nicotinic receptors in individual cholinergic terminals.

Ionotropic P2X receptors for ATP are formed, to date, by seven different subunits named P2X (Torres et al., 1999; Cunha and Ribeiro, 2000; North and Surprenant, 2000; Pintor et al., 2000; Hervás et al., 2003; Miras-Portugal et al., 2003; Illes and Ribeiro, 2004), which are cloned from various mammalian species (Illes and Ribeiro, 2004). These subunits can occur as homo- or hetero-oligomeric assemblies of more than one subunit (North and Surprenant, 2000), except P2X (Miras-Portugal et al., 2003) receptor, which has been described not to coassemble with other subunits (Torres et al., 1999). They are abundantly expressed in the peripheral and central nervous systems and exhibit high permeability to Ca2+ ions (Cunha and Ribeiro, 2000). The existence of presynaptic ionotropic receptors for nucleotides, either for ATP or dinucleotides, has been reported in isolated synaptic terminals from mammalian brain, and both exhibit good permeability to Ca2+ ions (Pintor et al., 2000; Hervás et al., 2003; Miras-Portugal et al., 2003). Studies on isolated single terminals have confirmed the existence of independent and specific responses to ATP and dinucleotides on the same or different terminals (Miras-Portugal et al., 1999; Díaz-Hernández et al., 2002; Hervás et al., 2005; Sánchez-Nogueiro et al., 2005). The activation of presynaptic ionotropic nucleotide receptors can induce the release of other neurotransmitters such as acetylcholine, glutamate, or GABA. In these specific terminals, ionotropic nucleotide receptors can be modulated by interaction with metabotropic receptors, such as GABAB and adenosine receptors (Khakh and Henderson, 1998; Gómez-Villafuertes et al., 2001), and ionotropic, such as nicotinic cholinergic receptors (Díaz-Hernández et al., 2004; Sánchez-Nogueiro et al., 2005). Here, we discuss a relevant finding on the interaction between ionotropic nucleotide and nicotinic receptors in cholinergic synaptic terminals and the role of CaCMKII in this interaction.