KCNQ potassium channel genes encode M-type potassium channels, and are notable because nearly all known human orthologs are associated with hereditary diseases, affecting epithelial cells, cardiac muscle and neurons. C. elegans possess three distinct KCNQ orthologs,
kqt-1 (C25B8.1),
kqt-2 (M60.5) and
kqt-3 (Y54G9a.3), among a total of 65 potassium channel genes. We examined the in vivo role for these channel genes through a combination of electrophysiological and genetic techniques. Our results revealed an unexpected role for intestinal KQT potassium channels in the control of defecation rhythms.
kqt-1 and
kqt-3 cRNAs expressed functional potassium currents in Xenopus oocytes, and were analyzed by voltage-clamp recordings. KQT-1 and KQT-3 currents exhibited particularly slow activation kinetics, depolarized voltage-dependence and pharmacological blocking profiles characteristic of KCNQ channels. Though
kqt-2 failed to express functional channels alone, co-injections with
kqt-1 or
kqt-3 suggest that KQT-2 is capable of forming heteromeric channels with either KQT-1 or KQT-3. This close resemblance of functional properties between KQT and KCNQ channel subunits, suggests that these two sets of genes may mediate similar conserved cellular functions in vivo . Consistent with a role for KCNQ channels in epithelial cells, kqt genes were found to express in worm intestine. Full-length translational GFP fusions were made for all three kqt genes and used to transform lines of worms. Intestinal cells were prominently labeled by
kqt-2 ::GFP and
kqt-3 ::GFP, with less consistent labeling by
kqt-1 ::GFP. Expression of
kqt-2 ::GFP was exclusive to intestinal cells, and appeared to label all cells uniformly. In contrast,
kqt-3 ::GFP expression was enhanced in anterior- and posterior-most intestinal segments. To examine intestinal kqt function, RNAi was performed for all three kqt genes and treated animals assayed for defecation behavior. Efficacy of RNAi-mediated suppression was independently confirmed for
kqt-2 and
kqt-3 , by the loss of intestinal GFP fluorescence reported by
kqt-2 ::GFP and
kqt-3 ::GFP transgenes. Suppression of either
kqt-2 or
kqt-3 resulted in prolonged defection cycle intervals (pBoc-to-pBoc), relative to N2 controls, with unaltered defecation motor steps. No effect was observed with
kqt-1 RNAi, consistent with weaker
kqt-1 ::GFP intestinal expression. Average cycle intervals were prolonged ~56% with
kqt-3 RNAi (75 +/- 6 sec) and ~28% with
kqt-2 RNAi (60 +/- 2 sec), relative to N2 (48 +/- 2 sec) and
kqt-1 RNAi (50 +/- 2 sec). Cycle interval histograms revealed bimodal normal distributions of intervals produced by
kqt-2 and
kqt-3 RNAi treated animals, with similar means (62 and 110 sec,
kqt-2 RNAi; 59 and 103 sec,
kqt-3 RNAi). This shared time structure suggests that KQT-2 and KQT-3 may act on a common process, perhaps as a heteromeric channel. This suggestion was further supported by double
kqt-2/kqt-3 RNAi experiments, showing prolonged cycle intervals (79 +/- 5 sec) which were non-additive relative to
kqt-3 and
kqt-2 RNAi treated animals. Because defecation cycles are controlled by intestinal cytoplasmic Ca +2 oscillations mediated by ITR-1 inositol triphosphate receptors, one intriguing possibility is that KQT channels may interact with this process. Thus, in addition to hypothesized roles in shaping prolonged action potentials and mediating ionic transport, our results suggest that KQT/KCNQ-like channels may serve an unexpected role in regulating intracellular calcium oscillations.