The Human Erythrocyte Mechano Activated K+ Channel A (HEMKCA) a Partial Characterization of Conductance, Selectivity and Open Probability

Abstract

Human Erythrocytes (HE) have a lifespan of 120 days, the control of this process has proven to be very rigorous. As the HE lacks nucleus and organelles, its lifespan is not controlled by a phenomena associated to classic apoptosis. How this process is controlled it's still under discussion: it's been proposed that this process is related to the fact that the membranes of these cells undergo a mechanical stress during microcirculation. Using the patch clamp technique we have characterized a K+ channel, which shows a sigmoid dependence of open probability (Po) on applied pressure, a mean conductance of 24 pS and is [Ca2+]i modulated; and we have proposed that this channel is the mechanical sensor that connects the mechanical stress on the cyclic passage through the capillaries with the process of senescence. We denominate this channel as: Human Erythrocyte Mechano-activated K+ Channel A (HEMKCA). Here we reviewed the behavior of this channel as an inward rectifier and the permeability of several ions. We study the selectivity in symmetrical conditions for K+, Rb+, Na+, Li+ and Cs+. In this condition we were unable to measure any conductance for Na+, Li+ or Cs+ through the channel. However, we determined that the conductance of HEMKCA for Rb+ is 0.59 times the conductance for K+. We also determined the selectivity sequence for these ions under bi-ionic conditions (PK/PX) with the test ion on the extracellular side: K+(1)>Rb+(1,49)>Cs+(16,36)>Li+(22,53)>Na+(34,95); and with the test ion on the intracellular side: K+(1)>Rb+(2,05)>Cs+(5,14)>Na+(11,89)> Li+(25,39). Finally we studied the effect of membrane potential on the channel's Po, and it was obtained that at negative membrane potentials the Po values are significantly higher than at positive potentials under the same experimental condition.