L. Varecka et al., THE PRESENCE OF H-LINKED CA2+ EXTRUDING SYSTEMS IN METHANOBACTERIUM-THERMOAUTOTROPHICUM( AND NA+), FEBS letters, 399(1-2), 1996, pp. 171-174
The effects of monovalent cations (Na+, K+ and choline(+)) and the unc
oupler 3,3',4',5-tetrachlorosalicylanilide (TCS) were tested on Ca-4S(
2+) uptake by non-energized cells of Methanobacterium thermoautotrophi
cum. Ca-45(2+) uptake was stimulated by the addition of K+ and (less)
by choline(+) while Na+ slowed down and even reversed it, thereby mimi
cking the energization of cells. The uncoupler agent, TCS, suppressed
Ca-45(2+) uptake in non-energized cells in the presence or absence of
Na+ but in cells energized in an atmosphere of CO2 + H-2 it exerted a
stimulating effect. Uncoupled Ca-45(2+) efflux was measured in cells p
re-loaded with Ca-45(2+) by means of the divalent ionophore A23187 fol
lowing its washing out by buffer containing serum albumin. The efflux
was temperature-dependent and was stimulated by external Ca-40(2+) and
Na+. In the absence of Na+, the uncoupled efflux was completely inhib
ited by TCS, whereas in the presence of Na+, TCS was without any effec
t. The results are in agreement with the model in which the Ca2+ influ
x pathway is represented by a membrane potential-driven uniport wherea
s Ca2+ efflux is mediated by two transport systems - Na+/Ca2+ and H+/C
a2+ antiporters whose participation in the total efflux is dependent o
n the energy of the corresponding gradients of driving ions.