Raising the intracellular level of inositol 1,4,5-trisphosphate changes plasma membrane ion transport in characean algae.

Abstract

Inositol 1,4,5‐trisphosphate (InsP3) was introduced into the cytoplasm of characean algae in two different ways: (i) by iontophoretic injection into cytoplasm‐enriched fragments from Chara and (ii) by adding InsP3 to the permeabilization medium of locally permeabilized cells of Nitella. In both systems this operation induced a depolarization of the membrane potential, ranging from a few mV to sequences of action potentials. The effect of InsP3 on locally permeabilized Nitella cells was abolished when InsP3 was added together with 30 mM EGTA. When inositol 1,4‐bisphosphate or myo‐inositol were substituted for InsP3 in this system, there was no change in the membrane potential. On the other hand, increasing the free Ca2+ concentration in the permeabilization medium induced, in a similar fashion to InsP3, action potentials. Similarities between InsP3 and Ca2+ action were also observed upon injection into Chara fragments. Both injections increased an inward current. In the first few seconds after injection the current/voltage characteristics of the InsP3‐induced current resembled those of the Ca2(+)‐sensitive current. Subsequently, differences between the InsP3‐ and Ca2(+)‐induced phenomena became apparent in that the InsP3‐induced current continued to increase while the Ca2(+)‐induced current declined, returning to the resting level. Our results suggest that these plant cells contain an InsP3 sensitive system that, under experimental conditions, is able to affect membrane transport via an increase in cytoplasmic free Ca2+.

Ca2+ Dynamics during Membrane Excitation of Green Alga Chara: Model Simulations and Experimental Data

“…These reveal that plants possess the key proteins and mechanisms for a stimulus-induced and IP 3 -mediated mobilization of Ca 2+ from internal stores (Sanders, Brownlee & Harper, 1999;Reddy, 2001). Also Chara cells most likely have such a signalling system, because it was shown that electrophoretic injection of IP 3 triggered membrane excitation (Thiel, MacRobbie & Hanke, 1990), while inhibition of phospholipase C abolished excitability of these cells (Biskup et al, 1999).…”

“…A large body of experimental evidence has precluded that voltage-dependent Ca 2+ influx via plasma membrane channels can be the primary source for the rise in Ca 2+ during excitation in Chara (Homann & Thiel, 1994;Thiel et al, 1997;Plieth et al 1998;Wacke & Thiel, 2001). The experimental data on the dynamics of ½Ca 2þ cyt as well as on the gating of the Ca 2+ -sensitive Cl À channels, which produce the depolarization of the action potential, can be best explained by a model in which a voltage-dependent production of a second messenger (Homann & Thiel, 1994;Thiel & Dityatev, 1998;Wacke & Thiel, 2001), most likely IP 3 (Thiel et al, 1990;Biskup et al, 1999), is triggering the release of Ca 2+ from internal stores. The above analysis of a combined model for voltagedependent production of such a second messenger and Ca 2+ mobilization from internal stores by IP 3 and Ca 2+ now allows successful simulation of the aforementioned body of experimental observations in the context of electrical excitation in plants.…”

Ion channel gating in plants: Physiological implications and integration for stomatal function

“…Findlay & Hope 1964;Lunevsky et al, 1983;Kataev, Zherelova & Berestovsky, 1984;Caldwell, Van Brunt & Harold, 1986;Shiina & Tazawa, 1988;Thiel, MacRobbie & Hanke, 1990; see also Tester, 1990); only very recently has attention turned to the presence of Cl-channels in traditionally nonexcitable higher-plant cells (Falke et al, 1987(Falke et al, , 1988Schauf & Wilson, 1987;Fairley & Walker, 1989; see also Okazaki & Tazawa, 1990). It is all the more striking, therefore, that a dominant theme among the recent discoveries is the role of Ca 2 + in activating or modulating channel current (Boult et al, 1989;Schroeder & Hagiwara, 1989;.…”

Novel Types of Ca2+ Release Channels Participate in the Secretory Cycle of Paramecium Cells

“…IP 3 and cyclic ADP-ribose induces Ca 2ϩ release in Euglena gracilis microsome fractions in a dose-dependent manner (61). In the giant algae Chara corallina and Nitrella translucens, IP 3 produces action potentials involving increased [Ca 2ϩ ] i (93). Treatment of vacuolar membrane vesicles from Candida albicans with IP 3 results in Ca 2ϩ release, blocked by heparin and ruthenium red (14).…”