Polyamines Depolarize the Membrane and Initiate a Cross-Talk Between Plasma Membrane Ca2+ and H+ Pumps

Abstract

There are multiple studies, exploring effects of polyamines on cation and K+ channels in animal and plant cells, but much less is known on their potential effects on cation-transporting ATPases. In this work non-invasive MIFE and conventional microelectrode techniques were applied to study the effects of polyamines (PAs) on Ca2+ and H+ transport and membrane potential in living pea roots. Putrescine (Put2+) or spermine (Spm4+) in 1 mM concentration caused a large increase of Ca2+ efflux across plasma membrane (PM), sensitive to Ca2+ pump inhibitor eosine yellow (EY) but insensitive to amiloride. Put2+ and Spm4+ caused contrasting effects on H+ fluxes: induced net H+ efflux (due to activity of the PM H+ pump) and influx, respectively. Use of EY and vanadate, non-specific inhibitor of P-type pumps, converted Spm4+-induced H+ influx to transient H+ efflux and suppressed H+ fluxes, respectively. The former result was consistent with Ca2+/H+ antiport activity of the PM Ca2+ pump. However, EY also reduced Put2+-induced H+ efflux. The latter result may be explained by down-regulation of the H+ pump activity by increased intracellular Ca2+. When it comes to direct effect of PAs on the H+ pump in isolated PM vesicles, Put2+ did not produce any effect and Spm4+ partly suppressed H+ pumping. All PAs, Spm4+>Spd3+>Put2+ caused substantial (up to 70 mV) membrane depolarization, abolished by Gd3+ and strongly decelerated by removal of external Ca2+. Analysis of net ion fluxes, induced by different PAs, led us to a conclusion that transport of PAs themselves directly contributes to membrane potential changes. Therefore, PAs induce Ca2+ pump activity and differentially affect H+ fluxes and electric potential difference across the PM. Supported by CONACyT and ARC grants and by University of Tasmania visiting professorship to IP.