Recruitment of plasma membrane voltage-dependent calcium-permeable channels in carrot cells.
Numerous biological assays and pharmacological studies have led to the suggestion that depolarization-activated plasma membrane Ca2+ channels play prominent roles in signal perception and transduction processes during growth and development of higher plants. The recent application of patch-clamp techniques to isolated carrot protoplasts has led to direct voltage-clamp evidence for the existence of Ca2+ channels activated by physiological depolarizations in the plasma membrane of higher plant cells. However, these voltage-dependent Ca2+ channels were not stable and their activities decreased following the establishment of whole-cell recordings. We show here that large pre-depolarizing pulses positive to 0 mV induced not only the recovery of Ca2+ channel activities, but also the activation of initially quiescent voltage-dependent Ca2+ channels in the plasma membrane (recruitment). This recruitment was dependent on the intensity and duration of membrane depolarizations, i.e. the higher and longer the pre-depolarization, the greater the recruitment. Pre-depolarizing pulses to +118 mV during 30 s increased the initial calcium currents 5- to 10-fold. The recruited channels were permeable to Ba2+ and Sr2+ ions. The data suggested that voltage-dependent Ca(2+)-permeable channels are regulated by biological mechanisms which might be induced by large pre-depolarizations of the plasma membrane. In addition, this study provides evidence for the existence in the plasma membrane of higher plant cells of a large number of voltage-dependent Ca2+ channels of which a major part are inactive and quiescent. It is suggested that quiescent Ca2+ channels can be rapidly recruited for Ca(2+)-dependent signal transduction.
Thuleau
P
P
Centre de Biologie et Physiologie Végétales, URA-CNRS 1457, Université Paul Sabatier, Toulouse, France.
Moreau
M
M
Schroeder
J I
JI
Ranjeva
R
R
D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000502:physiology*; D002413:Cations, Divalent / Q000378:metabolism; D002462:Cell Membrane / Q000502:physiology*; D002463:Cell Membrane Permeability / Q000502:physiology; D002478:Cells, Cultured; D018552:Daucus carota / Q000166:cytology / Q000502:physiology*; D015640:Ion Channel Gating; D018408:Patch-Clamp Techniques; D015398:Signal Transduction / Q000502:physiology*; D013997:Time Factors
D015220:Calcium Channels; D002413:Cations, Divalent; D002118:Calcium