Association/dissociation of a channel-kinase complex underlies state-dependent modulation.
Although ion channels are regulated by protein kinases, it has yet to be established whether the behavioral state of an animal may dictate whether or not modulation by a kinase can occur. Here, we describe behaviorally relevant changes in the ability of a nonselective cation channel from Aplysia bag cell neurons to be regulated by protein kinase C (PKC). This channel drives a prolonged afterdischarge that triggers the release of egg-laying hormone and a series of reproductive behaviors. The afterdischarge is followed by a lengthy refractory period, during which additional bursting cannot be elicited. Previously, we reported that, in excised inside-out patches, the cation channel is closely associated with PKC, which increases channel activity. We now show that this channel-kinase association is plastic, because channels excised from certain neurons lack PKC-dependent modulation. Although direct application of PKC-activating phorbol ester to these patches had no effect, exposing the neurons themselves to phorbol ester reinstated modulation, suggesting that an absence of modulation was attributable to a lack of associated kinase. Furthermore, modulation was restored by pretreating neurons with either PP1 [4-amino-5-(4-methylphenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine] or SU6656, inhibitors of Src tyrosine kinase, an enzyme whose Src homology 3 domain is required for channel-PKC association. Neurons that were stimulated to afterdischarge and had entered the prolonged refractory period were found to have more phosphotyrosine staining and less channel-PKC association than unstimulated neurons. These findings suggest that Src-dependent regulation of the association between the cation channel and PKC controls both the long-term excitability of these neurons and their ability to induce reproduction.
Magoski
Neil S
NS
Department of Physiology, Queen's University, Kingston, Ontario, K7L 3N6, Canada. magoski@post.queensu.ca
Kaczmarek
Leonard K
LK
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D001048:Aplysia; D002478:Cells, Cultured; D052078:Conus Snail; D007473:Ion Channels / Q000819:agonists / Q000378:metabolism*; D008978:Mollusk Venoms / Q000494:pharmacology; D009473:Neuronal Plasticity / Q000187:drug effects / Q000502:physiology*; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D011493:Protein Kinase C / Q000378:metabolism*
D007473:Ion Channels; D008978:Mollusk Venoms; D000255:Adenosine Triphosphate; D011493:Protein Kinase C