Calcium-dependent potassium channels control proliferation of cardiac progenitor cells and bone marrow-derived mesenchymal stem cells

Endogenous c-Kit(+) cardiac progenitor cells (eCPCs) and bone marrow (BM)-derived mesenchymal stem cells (MSCs) are being developed for cardiac regenerative therapy, but a better understanding of their physiology is needed. Here, we addressed the unknown functional role of ion channels in freshly isolated eCPCs and expanded BM-MSCs using patch-clamp, microfluorometry and confocal microscopy. Isolated c-Kit(+) eCPCs were purified from dog hearts by immunomagnetic selection. Ion currents were barely detectable in freshly isolated c-Kit(+) eCPCs with buffering of intracellular calcium (Ca-i(2+)). Under conditions allowing free intracellular Ca2+, freshly isolated c-Kit(+) eCPCs and ex vivo proliferated BM-MSCs showed prominent voltage-independent conductances that were sensitive to intermediate-conductance K+-channel (KCa3.1 current, I-KCa3.1) blockers and corresponding gene (KCNN4)-expression knockdown. Depletion of Ca-i(2+) induced membrane-potential (V-mem) depolarization, while store-operated Ca2+ entry (SOCE) hyperpolarized V-mem in both cell types. The hyperpolarizing SOCE effect was substantially reduced by I-KCa3.1 or SOCE blockade (TRAM-34, 2-APB), and I-KCa3.1 blockade (TRAM-34) or KCNN4-knockdown decreased the Ca2+ entry resulting from SOCE. I-KCa3.1 suppression reduced c-Kit(+) eCPC and BM-MSC proliferation, while significantly altering the profile of cyclin expression. I-KCa3.1 was reduced in c-Kit(+) eCPCs isolated from dogs with congestive heart failure (CHF), along with corresponding KCNN4 mRNA. Under perforated-patch conditions to maintain physiological [Ca2+](i), c-Kit(+) eCPCs from CHF dogs had less negative resting membrane potentials (-587mV) versus c-Kit(+) eCPCs from control dogs (-733mV, P<0.05), along with slower proliferation. Our study suggests that Ca2+-induced increases in I-KCa3.1 are necessary to optimize membrane potential during the Ca2+ entry that activates progenitor cell proliferation, and that alterations in KCa3.1 may have pathophysiological and therapeutic significance in regenerative medicine.