Figure 5.

Sequence analysis and expression of K2P channels in crab muscles

(A) Maximum likelihood phylogeny of mouse (Mm) and crab (Cb) K2P channels. Branch lengths are proportional to expected replacements per site. The alignment was constructed with the MAFFT model and phylogeny was inferred with the neighbor-joining method. Multiple sequence alignments are plotted for each protein where red indicates highly conserved positions and blue indicates lower conservation. The inset shows the alignment which spans the pore 1 domain. Indicated in bold red is the H98 residue known to confer pH sensitivity in mouse TASK-1 (MmKCNK3) and TASK-3 (MmKCNK9) channels and its conserved position in both crab channels.

(B) Amino acid alignment for the mouse and crab TASK channels. The four putative transmembrane domains (M1–M4) are highlighted in gray, while the two putative pore regions (P1 and P2) are highlighted in black. The K⁺ selectivity region of the pore is noted, and the red star indicates the pH sensitive H98 residue.

(C) Schematic diagram of TASK K2P channels. M1 to M4 are transmembrane segments and P1 and P2 are the pore-forming domains.

(D) Steady-state mRNA levels of CbKCNK1 and CbKCNK2 in crab muscle. Relative mRNA levels are shown for the putative two-pore K⁺ channels CbKCNK1 and CbKCNK2 from cpv1ab, gm5b, and gm6 muscle from individual animals. Each data point represents one tissue sample from one animal. For both genes, each sample is expressed as a fold difference relative to the median Cq value of the cpv1ab group. The horizontal lines represent the mean of the fold expression, and the vertical lines span the lower and upper limits of the standard error. There were no significant differences across muscle types for either gene.