Heterogeneity of ATP-sensitive K+ Channels in Cardiac Myocytes

Abstract

Ventricular KATP channels link intracellular energy metabolism to membrane excitability and contractility. We identified plakoglobin (PG) and plakophilin‐2 (PKP2) as KATP channel associated proteins and investigated whether the association of KATP channel subunits with junctional proteins translates to heterogeneous subcellular distribution within a cardiac myocyte. Co‐immunoprecipitation experiments confirmed physical interaction between KATP channels and PKP2 and PG in rat heart. Immunolocalization experiments demonstrated that KATP channel subunits are expressed at a higher density at the intercalated disk (ICD) in hearts, where they colocalized with PKP2 and PG. Super‐resolution microscopy demonstrate that KATP channels are clustered within nanometer distances from junctional proteins. The local KATP channel density was larger at the cell end when compared to local currents recorded from the cell's center. The KATP channel unitary conductance, block by MgATP and activation by MgADP did not differ between these two locations. Whole‐cell KATP channel current density was ~40% smaller in myocytes from mice haploinsufficient for PKP2. Experiments with excised patches demonstrated that the regional heterogeneity of KATP channels was absent in the PKP2 deficient mice, but the KATP channel unitary conductance and nucleotide sensitivities remained unaltered. Our data demonstrate heterogeneity of KATP channel distribution within a cardiac myocyte. The higher KATP channel density at the ICD implies a possible role at the intercellular junctions during cardiac ischemia. Funding from NIH HL085820.

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“…These images from each color channel were than superimposed to generate a 2 color superresolved image; the mapping error in this image was 20 nm. The 2 color mapping error obtained was found to be better than 20 nm, as we and others previously reported (39,40,(43)(44)(45).…”

“…For accurate alignment and mapping of the 2 color channels, diffraction-limited fluorescent beads were first imaged with emission spectra spanning both channels (Invitrogen). The location of the beads was matched for both channels, and a mapping matrix was generated using an IDL (Exelis Visual Information Solutions) custom mapping routine (39,40,(43)(44)(45). This mapping matrix superimposes the 2 sides of the image, each corresponding to a different color, into a 2-color image, and the images obtained were processed and analyzed using an ImageJ macro routine, which is based on the QuickPALM plugin (46).…”

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“…It is important to note that K ir 6.2 is also located at the intercalated disc and around the sarcolemma. (9) Therefore, the localization-dependent role of potassium channels as direct determinants of cardiac conduction merits further investigation.…”

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“…The disruption of the desmosomal complex in PKP2 deficient mice results in downregulation of K ATP channels, suggesting a possible role of these channels in cell-to-cell communication. 113 …”