Functional expression of SK channels in murine detrusor PDGFRα+ cells

We sought to characterize molecular expression and ionic conductances in a novel population of interstitial cells (PDGFR alpha(+) cells) in murine bladder to determine how these cells might participate in regulation of detrusor excitability. PDGFR alpha(+) cells and smooth muscle cells (SMCs) were isolated from detrusor muscles of PDGFR alpha(+)/eGFP and smMHC/Cre/eGFP mice and sorted by FACS. PDGFR alpha(+) 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 PDGFR alpha(+) cells in comparison to SMCs. alpha Slo (BK marker) was more highly expressed in SMCs. SK3 protein was observed in PDGFR alpha(+) 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 PDGFR alpha(+) cells under the same conditions. PDGFR alpha(+) 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 PDGFR alpha(+) 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 PDGFR alpha(+) cells. The apamin-sensitive stabilizing factor regulating detrusor excitability is likely to be due to the expression of SK3 channels in PDGFR alpha(+) cells because SK agonists failed to elicit resolvable currents and hyperpolarization in SMCs at physiological potentials.