Effect of Intracellular pH on the Mechano Activated Potassium Channel from Human Erythrocyte

Abstract

We have presented direct evidences of the existence of a Mechano-Activated K+ Channel in Human Erythrocytes (HEMKCA)(1). This channel presents a sigmoid dependence of Po on applied pressure and a conductance of 17pS in symmetrical 120mM KCl, 12mM NaCl, 1.8mM CaCl2, 10mM Tris, pH 7.3. We have proposed that this channel plays a fundamental roll in the senescent process of this cell, as the molecular mechanism behind to its biological clock (The K+ hypothesis). Because of the interplay of O2 and CO2 at microcirculation level it is expected a change in free H+ activity, and it is been already presented a difference in internal pH (pHi) between younger (pHi=7) and older cells (pHi=7.3)(2). Here, using the Patch-Clamp technique we have studied the effect of intracellular pH, ranging from 7.3 to 6.5, on the activity of HEMKCA. This decrease of pHi result in a dramatic decrease of Po, been equal to 0 at pHi lowers than 6.5. The open probability presents a sigmoid dependence on pH and can be described as a titration curve in concordance with the protonation of one or more independent sites, presenting a pK of 6.6, this suggests the involvement of the side-chain imidazole group of Histidine. The fact that there was no change in the channel conductance suggests that the titrated site(s) is not close to the mouth, the vestibule or the pore of the channel. In conclusion, we present a dramatic dependence of Po with pHi, so in younger cells the channel activity is naturally depressed compared with older cells in concordance with the K+ hypothesis presented by us.(1) Romero, J.G. and Romero, P.J.(2005)Biophysical J. 88(1): 266a(2) Romero, P.J. and Romero E. (2004) Act Cient Venez. 55(1):83,5