External electric fields stimulate the electrogenic calcium/sodium exchange in plant protoplasts

• Published in: Biochemistry (Easton) Vol. 29; no. 36; pp. 8313 - 8318
• Main Authors: Graziana, Annick, Ranjeva, Raoul, Teissie, Justin
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 11-09-1990
• Subjects: ABSORCION DE SUBSTANCIAS NUTRITIVAS; ABSORPTION DE SUBSTANCES NUTRITIVES; Adenosine Triphosphate - metabolism; Animals; Biological and medical sciences; Biological Transport, Active; CALCIO; CALCIUM; Calcium - metabolism; Calcium Channels - metabolism; Cell physiology; DAUCUS CAROTA; Electric Stimulation; ESTIMULO; Fundamental and applied biological sciences. Psychology; Ion Channel Gating; MEMBRANA; MEMBRANE; Membrane and intracellular transports; MEMBRANE POTENTIAL; Membrane Potentials; MEMBRANES; Molecular and cellular biology; NUTRIENT UPTAKE; Plant Proteins - metabolism; Proton-Translocating ATPases - metabolism; PROTOPLASTE; PROTOPLASTOS; PROTOPLASTS; Protoplasts - metabolism; Second Messenger Systems; sodium; Sodium - metabolism; STIMULI; STIMULUS; Temperature; Vegetals; Calcium; Saturation; Electrical stimulus; Ion transport; Fluorescence spectrometry; Sodium; Morphology; Protoplast; Plasma membrane; Kinetics; Integrity; Atomic absorption spectrometry
• ISSN: 0006-2960; 1520-4995
• DOI: 10.1021/bi00488a016

External electric fields of low intensity stimulated calcium influx in protoplasts isolated from carrot cell suspension cultures in field intensity dependent and frequency-dependent ways. The field-induced calcium uptake involved a temperature-dependent system that was saturable by external calcium. The induction process appeared mainly cumulative as long as the morphology of the protoplasts did not change (up to 10 min). The stimulation elicited by the electric fields was effective even after switching the field off; the influx increased for 5 min and then slowed down to its initial value 15 min later. During electrostimulation, an additional amount of ATP was accumulated; on removal of the stimulatory field, the extra amount of ATP was consumed, whereas the plasma membrane was hyperpolarized and sodium ions were expelled from the protoplasts. Inhibition of either ATP accumulation or consumption results in the inhibition of both calcium influx and sodium efflux, demonstrating that these processes are coupled. From the data obtained in this work, it may be concluded that the electric field stimulates an ATP synthase like activity; the consumption of the ATP thus formed elicits an electric potential (probably due to the efflux of cations and more specifically sodium) that drives the influx of calcium.