Recruitment of plasma membrane voltage-dependent calcium-permeable channels in carrot cells.

Abstract

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.

Activation of plasma membrane voltage‐dependent calcium‐permeable channels by disruption of microtubules in carrot cells

“…In addition to their low activities, VDCCs are very unstable following the establishment of the whole-cell configuration [8,9]. As shown in Fig.…”

“…Since they couple the perception of an initial stimulus to a regulated pathway for calcium influx into plant cells, plasma membrane-bound voltage-dependent calcium-permeable channels (VDCCs) may be important targets in cell signalling [2][3][4]. While their existence has been inferred from indirect approaches for years [5], the characterization of depolarization-activated Ca 2+ channels located in the plasma membrane has been established only recently [6][7][8][9][10]. So far, measurements of voltage-operated calcium movements either through plasma membrane derived vesicles or by application of whole-cell patch-clamp technique to isolated protoplasts have established that voltage-dependent inward calcium currents can be activated by physiologically occurring depolarizations in different plants [6][7][8]10].…”

“…However, activities of VDCCs were measurable in approx. 2-3 carrot protoplasts out of 10 only and decreased rapidly following the establishment of whole-cell recordings [8,9]. Attempts to stabilize and/or to enhance calcium currents have shown that large transient pre-depolarizations of the plasma membrane potentiate the activity of carrot calcium channels [9].…”

“…2-3 carrot protoplasts out of 10 only and decreased rapidly following the establishment of whole-cell recordings [8,9]. Attempts to stabilize and/or to enhance calcium currents have shown that large transient pre-depolarizations of the plasma membrane potentiate the activity of carrot calcium channels [9]. Thus, predepolarizing pulses positive to 0 mV induced not only the recovery of calcium channel activities but also the activation of initially quiescent channels by a process referred to as recruitment.…”

“…Thus, predepolarizing pulses positive to 0 mV induced not only the recovery of calcium channel activities but also the activation of initially quiescent channels by a process referred to as recruitment. Recruitment of quiescent channels may allow flexibility to plant cells to gate the flow of calcium in response to a number of depolarizing stimuli [9].…”