A Kinetic Characterization of the Human Erythrocyte Mechano-Activated K+ Channel Inactivation Process

Abstract

Human erythrocyte (hRBC) shows a live span of 120 days, as these cells lack nucleus and organelles a question arises: which is the subjacent molecular process to this tightly controlled programme cell death (the biological clock)? It has been proposed that the increased Ca2+ concentration characteristic of the senescent cells is due to a mechanical stress at the microcirculation level. Using the Patch Clamp Technique, we had characterized a mechano-activated K+ channel which shows a sigmoid dependence of Po on applied pressure, a mean conductance of 17pS, and is Ca2+ modulated (140mMKCl, 10mMNaCl, 1mMCaCl2, pH7.0)(HEMKCA)(1,2), and had proposed a new hypothesis for the senescent process of hRBC with this channel as the responsible for the molecular clock. This channel presented an inactivation process producing an exponential decay of Po (τ=4.55±1.95min). Here we present a complete kinetically characterization of this inactivation process: intriguingly, this process seemed to begin just when a voltage step is applied and ionic current started, suggesting that the activation process is necessary but not sufficient to allow the inactivation development. We had characterized the burst mode activity of this channel (17.43±17.15 events/burst, 264.27±291.3ms burst duration and 15.67±7.1ms intraburst interval). The decay in Po produced by the inactivation seemed to be the effect of decay in the number of events per burst, probably related to burst duration decay, with no effect in intrabursts variables like intraburst intervals and intraburst mean duration. We present a complete kinetic model for this channel with two independent kinetic branches: one for the non-inactivated mode and the other for the inactivation pathway. This inactivation mechanism is presented as a molecular damper (security system) in our new hypothesis for the hRBC senescence. (1)(2005) Biophys. J.88(1):593 (2)(2008) Biophys. J.91(1):1101 CDCH PI 03-00-6135-2008