Endogenous expression of TRPV5 and TRPV6 calcium channels in human leukemia K562 cells

Abstract

In blood cells, changes in intracellular Ca(2+) concentration ([Ca(2+)](i)) are associated with multiple cellular events, including activation of cellular kinases and phosphatases, degranulation, regulation of cytoskeleton binding proteins, transcriptional control, and modulation of surface receptors. Although there is no doubt as to the significance of Ca(2+) signaling in blood cells, there is sparse knowledge about the molecular identities of the plasmalemmal Ca(2+) permeable channels that control Ca(2+) fluxes across the plasma membrane and mediate changes in [Ca(2+)](i) in blood cells. Using RNA expression analysis, we have shown that human leukemia K562 cells endogenously coexpress transient receptor potential vanilloid channels type 5 (TRPV5) and type 6 (TRPV6) mRNAs. Moreover, we demonstrated that TRPV5 and TRPV6 channel proteins are present in both the total lysates and the crude membrane preparations from leukemia cells. Immunoprecipitation revealed that a physical interaction between TRPV5 and TRPV6 may take place. Single-channel patch-clamp experiments demonstrated the presence of inwardly rectifying monovalent currents that displayed kinetic characteristics of unitary TRPV5 and/or TRPV6 currents and were blocked by extracellular Ca(2+) and ruthenium red. Taken together, our data strongly indicate that human myeloid leukemia cells coexpress functional TRPV5 and TRPV6 calcium channels that may interact with each other and contribute into intracellular Ca(2+) signaling.

Non-Selective Cation Channel-Mediated Ca²⁺-Entry and Activation of Ca²⁺/Calmodulin-Dependent Kinase II Contribute to G₂/M Cell Cycle Arrest and Survival of Irradiated Leukemia Cells

“…In the present study, the Ca 2+ -permeable nonselective cation channels activated by IR exhibited a strongly inwardly rectifying currentvoltage relationship highly reminiscent of Ca 2+ -selective TRPV5 and -V6 channels [21]. In K562 cells, TRPV5 and -V6 proteins may form functional heterotetrameric channels [7]. They are permeable for monovalent cations [22], and the monovalent cation currents are inhibited by micromolar concentrations of extracellular Ca 2+ [7] suggestive of a competition of monovalent and Ca 2+ cations within the channel pore.…”

“…Functional expression of cAMP-stimulated CFTR [16] and oxidation-induced ClC-3 anion channels [17], voltagegated hERG1 [18] and Ca 2+ -activated SK4 (KCa 3.1 ) K + channels [19], TRPC7 [20] and TRPV5 and -V6 nonselective cation channels [7] have been defined in K562 cells on the molecular level. In the present study, the Ca 2+ -permeable nonselective cation channels activated by IR exhibited a strongly inwardly rectifying currentvoltage relationship highly reminiscent of Ca 2+ -selective TRPV5 and -V6 channels [21].…”

“…The high relative Ca 2+ permeability and the strong inward rectification resemble properties of TRPV5/6 channels. Monovalent cation currents through these channels have been demonstrated in K562 cells to be effectively inhibited by micromolar concentrations of extracellular Ca 2+ [7]. We therefore recorded control and irradiated K562 cells with K-gluconate pipette and Nagluconate bath solution and modified the extracellular free Ca 2+ concentration.…”

“…In addition, expression of TRPV5/6 channels has been reported in a CML cell line [7]. CML is commonly defined by the presence of the Philadelphia chromosome, a reciprocal translocation of chromosomes 9 and 22.…”

Physical Exercise in Patients with Severe Kidney Disease

“…This conclusion is reinforced by the results of another programme in North Staffordshire, UK: after more than 4,000 individual intradialytic exercise sessions and over 300 peak exercise tests, there was only 1 case of clinically severe autonomic dysregulation [101]. Diabetic patients may have an increased risk of such autonomic dysregulation [102] but, in a group of African-American men identified as at increased risk of diabetes, the long-term effect of resistance exercise was shown to be suppression of autonomic dysregulation [103]. Furthermore, even though patients with renal failure frequently present with co-morbidities such as coronary artery disease, cerebrovascular disease, PVD, COPD, and cancer [1,95], and these may contribute to physical inactivity, these do not necessarily exclude the patients from appropriate exercise programmes.…”