A calcium-selective channel from root-tip endomembranes of garden cress

A Ca2+ channel from root-tip endomembranes of garden cress (Lepidium sativu m L.) (LCC1) was characterized using the planar lipid-bilayer technique. In vestigation of single-channel recordings revealed that LCC1 is voltage gate d and strongly rectifying. In symmetrical 50 mM CaCl2 solutions, the single -channel conductance was 24 picosiemens. LCC1 showed a moderate selectivity for Ca2+ over K+ (9.4:1) and was permeable for a range of divalent cations (Ca2+, Ba2+, and Sr2+). In contrast to Bryonia dioica Ca2+ channel 1, a Ca 2+-selective channel from the endoplasmic reticulum of touch-sensitive tend rils, LCC1 showed no bursting channel activity and had a low open probabili ty and mean open time (2.83 ms at 50 mV). Inhibitor studies demonstrated th at LCC1 is blocked by micromolar concentrations of erythrosin B (inhibitor concentration for 50% inhibition [IC50] = 1.8 mu M) and the trivalent catio ns La3+ (IC50 = 5 mu M) and Cd3+ (IC50 = 10 mu M), whereas verapamil showed no blocking effect. LCC1 may play an important role in the regulation of t he cytoplasmic free Ca2+ concentration in root-tip and/or root-cap cells. T he question of whether this ion channel is part of the gravitropic signal t ransduction pathway deserves further investigation.