H+-mediated coupling of transmembrane Ca2+ fluxes in vegetative Trichoderma viride mycelia suggested by the study of ageing and adaptation to extreme Ca2+ concentrations

The adaptation to extreme concentrations of Ca2+ and its consequence on the properties of the 45Ca2+ transport were studied in submerged mycelia of Trichoderma viride. The adaptation to low [Ca2+]o did not cause changes in kinetic parameters of the 45Ca2+ influx but the adaptation to high [Ca2+]o increased the KM(Ca2+). The Vmax of the 45Ca2+ influx decreased with the age of (non-adapted) mycelia with concomitant decrease of the KM(Ca2+) these changes were prevented in mycelia adapted to high Ca2+. High [Ca2+]o decreased the stimulation by the uncoupler, 3, 3′, 4′, 5-tetrachloro salicylanilide (TCS) (30 μM), as compared to the control, whereas the Ca2+ chelator, EGTA, stimulated it. In the aged mycelia, the stimulation by TCS of the 45Ca2+ influx faded away, in parallel with the activity of the H+-ATPase. The 45Ca2+ efflux from mycelia was affected by TCS in a similar way as the 45Ca2+ influx. The results demonstrate the adaptive responses of transport processes participating in the mycelial Ca2+ homeostasis and ageing are in agreement with a notion that both Ca2+-influx and-efflux are coupled by the H+-homeostasis at the plasma membrane.