Functional expression of SK channels in murine detrusor PDGFRα+ cells

Authors


S. D. Koh: Department of Physiology and Cell Biology, University of Nevada School of Medicine, 1664 N. Virginia St MS 0352, Reno, NV 89557, USA. Email: skoh@medicine.nevada.edu

Key points

  • • SK currents have been recorded from detrusor smooth muscle cells, but current density at physiological holding potentials is negligible.
  • • We discovered a new class of interstitial cell in the bladder that were identified using antibodies against platelet-derived growth factor receptor-α(PDGFRα+ cells).
  • • SK3 channel transcripts and protein are highly expressed in PDGFRα+ cells in comparison to smooth muscle cells.
  • • Current density attributable to SK-like currents is much higher in PDGFRα+ cells than in smooth muscle cells. Single channel currents, consistent with the conductance and Ca2+ sensitivity of SK3 channels were measured in PDGFRα+ cells.
  • • The abundance of SK3 channels in PDGFRα+ cells in detrusor muscles suggests that PDGFRα+ cells, not SMCs, provide apamin-sensitive regulation of detrusor excitability.

Abstract  We sought to characterize molecular expression and ionic conductances in a novel population of interstitial cells (PDGFRα+ cells) in murine bladder to determine how these cells might participate in regulation of detrusor excitability. PDGFRα+ cells and smooth muscle cells (SMCs) were isolated from detrusor muscles of PDGFRα+/eGFP and smMHC/Cre/eGFP mice and sorted by FACS. PDGFRα+ cells were highly enriched in Pdgfra (12 fold vs. unsorted cell) and minimally positive for Mhc (SMC marker), Kit (ICC marker) and Pgp9.5 (neuronal marker). SK3 was dominantly expressed in PDGFRα+ cells in comparison to SMCs. αSlo (BK marker) was more highly expressed in SMCs. SK3 protein was observed in PDGFRα+ cells by immunohistochemistry but could not be resolved in SMCs. Depolarization evoked voltage-dependent Ca2+ currents in SMCs, but inward current conductances were not activated in PDGFRα+ cells under the same conditions. PDGFRα+ cells displayed spontaneous transient outward currents (STOCs) at potentials positive to −60 mV that were inhibited by apamin. SK channel modulators, CyPPA and SKA-31, induced significant hyperpolarization of PDGFRα+ cells and activated SK currents under voltage clamp. Similar responses were not resolved in SMCs at physiological potentials. Single channel measurements confirmed the presence of functional SK3 channels (i.e. single channel conductance of 10 pS and sensitivity to intracellular Ca2+) in PDGFRα+ cells. The apamin-sensitive stabilizing factor regulating detrusor excitability is likely to be due to the expression of SK3 channels in PDGFRα+ cells because SK agonists failed to elicit resolvable currents and hyperpolarization in SMCs at physiological potentials.

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