Gadolinium-sensitive, voltage-dependent calcium release channels in the endoplasmic reticulum of a higher plant mechanoreceptor organ.
The lipid bilayer technique was adapted to the functional reconstitution of ion channels from the endoplasmic reticulum of a higher plant. This was obtained at high purity from touch-sensitive tendrils of Bryonia dioica. In this preparation, a calcium-selective strongly rectifying channel is prevailing whose single-channel properties have been characterized. The single-channel conductance is 29 pS in 50 mM CaCl2. The Ca2+: K+ selectivity was determined to be approximately 6.6. The channel is voltage-gated and, more importantly, the gating voltage is strongly shifted towards more negative voltages when a transmembrane Ca2+ gradient is applied. Thus, at physiological voltages across the endoplasmic reticulum membrane, the channel's open probability will be governed largely by the chemical potential gradient of Ca2+, generated by the Ca(2+)-ATPase in that same membrane. The calcium release channel described here is effectively blocked by Gd3+ which also completely suppresses a tendril's reaction to touch, suggesting that this channel could be a key element of calcium signaling in higher plant mechanotransduction. Its molecular characteristics and inhibitor data show it to be the first known member of a hitherto unrecognized class of calcium channels.
Klüsener
B
B
Department of Plant Physiology, Ruhr-University, Bochum, Germany.
Boheim
G
G
Liss
H
H
Engelberth
J
J
Weiler
E W
EW
D002118:Calcium / Q000494:pharmacology; D015220:Calcium Channels / Q000502:physiology*; D004721:Endoplasmic Reticulum / Q000502:physiology*; D004923:Erythrosine / Q000494:pharmacology; D005682:Gadolinium / Q000494:pharmacology*; D015640:Ion Channel Gating / Q000187:drug effects*; D018520:Plant Shoots / Q000502:physiology*; D014700:Verapamil / Q000494:pharmacology
D015220:Calcium Channels; D005682:Gadolinium; D014700:Verapamil; C038958:gadolinium chloride; D004923:Erythrosine; D002118:Calcium