A Tight-Seal Whole Cell Study of the Voltage-Dependent Gating Mechanism of K⁺-Channels of Protoplasmic Droplets of Chara corallina

Abstract

The biophysical properties of voltage-dependent K+-channels of pro- (e.g. 8, 19, 26, 27), and that potassium ions are the main species transported in the leakage current (2). K+-channels also play a role in the light-induced membrane potential change in perfused Chara corallina cells (30) and in Eremosphaera viridis (17). Ion transpot through the plant cell membrane has also been studied by noise analysis of the membrane potential (6,(22)(23)(24). The minus two slope of the voltage noise power spectrum has been attributed to the activity of K+-channels (6). More recently the patch-clamp technique has been used to study the properties of a single K+-channel isolated from the plasmalemma of guard cells of Vicia faba (25) and of the membrane surrounding protoplasmic droplets of C. corallina cells (13).In the present work the time-and voltage-dependence of K+-channels were investigated on protoplasmic droplets by means of the tight-seal whole cell technique (9) which allows the intracellular ionic composition to be controlled. Two K+-channel activities with different time-and voltage-dependent characteristics were identified.

Calcium-activated, voltage-dependent, non-selective cation currents in endosperm plasma membrane from higher plants

“…The membrane enclosing these cyto plasmic droplets has been shown to be tonoplastic in origin (Sakano & Tazawa 1986;Liihring 1986), although this remains controversial (cf. Homble 1987). For example, Krawczyk (1978) observed single 10 pS, non-selective monovalent cation channels (with 100 mM solutions), most active at depolarized potentials, in mem brane patches formed after insertion of a microelectrode into Nitella cytoplasm, similar to the channel reported here.…”

“…Outward K currents from membrane-bound cytoplasmic droplets of the giant algal cells N i t e l l a and Chara have been also found (Liihring 1986 ;Homble 1987;Homble et al 1987;Laver & Walker 1987). The membrane enclosing these cyto plasmic droplets has been shown to be tonoplastic in origin (Sakano & Tazawa 1986;Liihring 1986), although this remains controversial (cf.…”

Tansley Review No. 21 Plant ion channels: whole‐cell and single channel studies

“…In contrast, Minorsky et al (1989) found cation selective channels patch clamped in the onoplast of the same species, Saccharomyces cerevisiae, were insensitive to large changes in the 'cytoplasmic' Ca^^ activity. '• K^ channels in cytoplasmic droplets from charophytes channels have been frequently measured in cytoplasmic droplets (see V. 2) from cells of Chara allina {l^uhring, 1986;Homble, 1987;Homble, Ferrier & Damty, 1987;Laver & Walker, 1987;l>erman & Findlay, 1989 a;Bertl, 1989;Bisson, Tyerman & Findlay, 1989;Katsuhara, Mimura o^ Tazawa, 1989;Laver et al, 1989). The most common channel in the droplet membrane is voltage dependent, has a high unitary G (about 170 pS in 150 mM KCl), and is generally strongly selective for K+ (Luhring, 1986;Laver & Walker, 1987;Bertl, 1989;leaver etal., 1989;Katsuhara et al, 1989).…”

Coupling of water and potassium ions in K+ channels of the tonoplast of Chara

“…Cytoplasmic droplets formed from Chara are covered by a membrane derived from the tonoplast (Lihring, 1986;Sakano and Tazawa, 1986). The passive conductance ofthis vacuolar membrane is largely dominated by a potassium conductance (Homble, 1987).…”