The K+ channel openers diazoxide and NS1619 induce depolarization of mitochondria and have differential effects on cell Ca2+ in CD34+ cell line KG-1a (original) (raw)

Objective. Mitochondrial membrane potential (Dy m ) and intracellular Ca 2ϩ play a crucial role in growth and differentiation in hemopoiesis. Some potassium channel openers such as diazoxide have the capacity to elevate cytosolic Ca 2ϩ and depolarize mitochondria in cardiomyocytes. To clarify if such substances have effects on hemopoietic cells we investigated the commonly used opener of the mitoK ATP channel, diazoxide, and the opener of BK channels, NS1619, for their potential to depolarize mitochondria, elevate cytosolic Ca 2ϩ , and induce apoptosis in the hemopoietic CD34 ϩ cell line KG-1a. Methods. Fluorescent probes were used to investigate Dy m , free Ca 2ϩ , and apoptosis (JC-1, fluo-3-AM and annexin V-FITC) by flow cytometry. To measure Dy m with JC-1 in glycoprotein P ϩ cells we used an improved dye loading technique with verapamil. Results. NS1619 induced stronger dose-dependent mitochondrial depolarizations than diazoxide. Depolarization was independent from caspase activation and could also be induced when the driving force for K ϩ out of cells was near 0 mV. In Ca 2ϩ free solutions NS1619 induced stronger Ca 2ϩ elevations than diazoxide and elevated Ca 2ϩ also after Ca 2ϩ depletion of the endoplasmatic reticulum with caffeine. NS1619 did not enhance the Ca 2ϩ elevation induced by ionophores (CCCP, valinomycin) that depolarize mitochondria. Both agents were weak inducers of apoptosis. Conclusion. Diazoxide has similar effects in CD34 ϩ cells as described for muscle or nerve cells. In accordance to the single channel conductance of mitoK ATP and BK channels, NS1619 is a more potent inducer of mitochondrial depolarization than diazoxide. NS1619 releases Ca 2ϩ from an intracellular pool that is insensitive to caffeine but depends strongly on Dy m . Ć