Ionic mechanisms of central CO2 chemosensitivity

Abstract

A comparative analysis of chemosensory systems in invertebrates and vertebrates reveals that different animals use similar strategies when sensing CO 2 to control respiration. A variety of animals possess neurons that respond to changes in pH. These respiratory chemoreceptor neurons seem to rely largely on pH-dependent inhibition of potassium channels, but the channels do not appear to be uniquely adapted to detect pH. The 'chemosensory' potassium channels identified thus far are widely distributed, common potassium channels. The pH-sensitivity is a common feature of the channels whether the channels are in chemosensory neurons or not. Thus, the pattern of synaptic connectivity and the mix of potassium channels expressed seem to determine whether a neuron is chemosensory or not, rather than any special adaptation of a channel for pHsensitivity. Moreover, there are often multiple pH-sensitive channels in each chemosensory neuron. These ionic mechanisms may, however, be only part of the chemosensory process, and pH-dependent modulation of synaptic activity seems to contribute to central chemosensitivity as well. In addition, the exploration of the mechanisms of pH-dependent modulation of ion channel activity in chemosensory cells is incomplete: additional mechanisms of pH modulation of channel activity may be found, and addition conductances, other than potassium channels, may participate in the chemosensory process.

Redefining the components of central CO2 chemosensitivity – towards a better understanding of mechanism

“…Several recent reviews summarize current knowledge of chemosensory reflexes and mechanisms (Chernov et al 2010;Darnall, 2010;Dean & Putnam, 2010;Duffin, 2010;Erlichman et al 2010;Gargaglioni et al 2010;Goridis & Brunet, 2010;Guyenet & Mulkey, 2010;Hodges & Richerson, 2010;Kc & Martin, 2010;Kuwaki et al 2010;Milsom, 2010;Nattie & Forster, 2010;Patwari et al 2010;Smith et al 2010;Ray et al 2011). Our purpose is slightly different: to re-examine the current assumptions and arrive at new approaches to analyse and understand the apparent complexity underlying chemosensory mechanisms.…”

“…Several recent reviews summarize current knowledge of chemosensory reflexes and mechanisms ( Chernov et al . 2010 ; Darnall, 2010 ; Dean & Putnam, 2010 ; Duffin, 2010 ; Erlichman et al .…”

TASK-2: a K2P K+ channel with complex regulation and diverse physiological functions

“…On the other hand, TASK-2 sensitivity to extra- and/or intracellular pH might play roles in a putative function of the channel as a pH/CO 2 sensor in RTN neurons, particularly since the last property would allow TASK-2 to behave as a CO 2 sensor (Niemeyer et al, 2010). It must be pointed out that the role of TASK-2 in central chemosensing has been put in doubt (Chernov et al, 2010; Guyenet et al, 2010). It is argued that TASK-2 ablation, in contrast to what is seen after deletion of RTN neurons, does not produce the expected alteration in pH sensitivity of the neonate breathing network in vitro .…”

Introduction to special issue, “How nature shaped echolocation in animals”

“…On the other hand, TASK-2 sensitivity to extra-and/or intracellular pH might play roles in a putative function of the channel as a pH/CO 2 sensor in RTN neurons, particularly since the last property would allow TASK-2 to behave as a CO 2 sensor (Niemeyer et al, 2010). It must be pointed out that the role of TASK-2 in central chemosensing has been put in doubt (Chernov et al, 2010;. It is argued that TASK-2 ablation, in contrast to what is seen after deletion of RTN neurons, does not produce the expected alteration in pH sensitivity of the neonate breathing network in vitro.…”