The human erytrocyte mechano-activated K+ channel A (HEMKCA): Effectof interaction of intracellular calcium and pH on conduction and kineticsvariables. A partial study.

Abstract

Human erythrocytes (HRBC) have a half-lifespan of 120 days; however, as anucleated cells, they cannot undergo a classical apoptosis. Therefore, the question arises: What are the mechanisms that allow a strict control of the lifespan? We have proposed a new hypothesis for the senescence of HRBC, in which the cyclic passage through the capillaries and its concomitant mechanical stress would be the mechanism that allows counting lifetime. In this sense, in our laboratory we have characterized for the first time a potassium channel sensitive to mechanical stress, the human erythrocyte mechano-activated channel A (HEMKCA), which we assume to be the molecular mechanism behind the biological clock of these cells. It has an average conductance of 20 pS and presents a clear dependence of Po on calcium. We have also shown a clear effect of internal pH on channel activity. In this work, we present the study of the effect of the joint change of pH and Ca on the activity of the channel. Using pH values of 6.0, 6.3, 6.5, 6.8, 7.0 and 7.4 and Ca2+ concentration of 100 nM, 1 µM, 50 µM, 100 µM and 1 mM. For this study, we measured the channel activity with Patch Clamp, activating the channel with pressure under asymmetric pH conditions starting with pH 6.0 inside and 7.4 outside, at a membrane potential of −60 mV. The most outstanding result is that at acidic pH the channel activity modulation by Ca is lost; however, the inactivation process at acidic pH depends on the concentration of Ca2+, becoming slower at higher concentrations of Ca2+, and it was also observed that as internal pH basifies, the inactivation process develops more slowly regardless of the Ca2+ concentration.