Mechanosensitive cation channels in human leukaemia cells: calcium permeation and blocking effect.
Cell-attached and inside-out patch-clamp methods were employed to identify and characterize mechanosensitive (MS) ionic channels in the plasma membrane of human myeloid leukaemia K562 cells. A reversible activation of gadolinium-blockable mechanogated currents in response to negative pressure application was found in 58 % of stable patches (n = 317). I-V relationships measured with a sodium-containing pipette solution showed slight inward rectification. Data analysis revealed the presence of two different populations of channels that were distinguishable by their conductance properties (17.2 +/- 0.3 pS and 24.5 +/- 0.5 pS), but were indistinguishable with regard to their selective and pharmacological properties. Ion-substitution experiments indicated that MS channels in leukaemia cells were permeable to cations but not to anions and do not discriminate between Na(+) and K(+). The channels were fully impermeable to large organic cations such as Tris(+) and N-methyl-D-glucamine ions (NMDG(+)). Ca(2+) permeation and blockade of MS channels were examined using pipettes containing different concentrations of Ca(2+). In the presence of 2 mM CaCl(2), when other cations were impermeant, both outward and inward single-channel currents were observed; the I-V relationship showed a unitary conductance of 7.7 +/- 1.0 pS. The relative permeability value, P(Ca)/P(K), was equal to 0.75, as estimated at physiological Ca(2+) concentrations. Partial or full inhibition of inward Ca(2+) currents through MS channels was observed at higher concentrations of external Ca(2+) (10 or 20 mM). No MS channels were activated when using a pipette containing 90 mM CaCl(2). Monovalent mechanogated currents were not significantly affected by extracellular Ca(2+) at concentrations within the physiological range (0-2 mM), and at some higher Ca(2+) concentrations.
Staruschenko
Alexandr V
AV
Institute of Cytology, Russian Academy of Sciences, 194064, St Petersburg, Russia. star@mail.cytspb.rssi.ru
Vedernikova
Elena A
EA
D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology*; D015220:Calcium Channels / Q000378:metabolism; D002462:Cell Membrane / Q000502:physiology; D004594:Electrophysiology; D006801:Humans; D015640:Ion Channel Gating / Q000502:physiology; D007473:Ion Channels / Q000037:antagonists & inhibitors / Q000187:drug effects / Q000502:physiology*; D020014:K562 Cells; D007938:Leukemia / Q000503:physiopathology*; D008465:Mechanoreceptors / Q000187:drug effects / Q000502:physiology*; D008564:Membrane Potentials / Q000502:physiology; D018408:Patch-Clamp Techniques; D010539:Permeability; D011188:Potassium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism
D015220:Calcium Channels; D007473:Ion Channels; D012964:Sodium; D011188:Potassium; D002118:Calcium