title: Calcium activation of mougeotia potassium channels.
abstract: Phytochrome mediates chloroplast movement in the alga Mougeotia, possibly via changes in cytosolic calcium. It is known to regulate a calcium-activated potassium channel in the algal plasma membrane. As part of a characterization of the potassium channel, we examined the properties of calcium activation. The calcium ionophore A23187 activates the channel at external [Ca(2+)] as low as 20 micromolar. However, external [Ca(2+)] is not required for activation of the channel by photoactivated phytochrome. Furthermore, when an inhibitor of calcium release from internal stores, 8-(diethylamino)-octyl-3,4,5-trimethoxybenzoate, hydrochloride (TMB-8), is present, red light no longer stimulates channel activity. We conclude that phytochrome activates the plasma membrane potassium channel by releasing calcium from intracellular calcium vesicles; the elevated cytosolic calcium then stimulates channel activity by an unknown mechanism. In the presence of TMB-8, red light does induce chloroplast rotation; thus, potassium channel activation may not be coupled to chloroplast rotation.
authors: Purdue University School of Science at Indianapolis, Department of Biology, Indianapolis, Indiana 46223.
authors: R R
authors: RR
authors: Lew
authors: B S
authors: BS
authors: Serlin
authors: C L
authors: CL
authors: Schauf
authors: M E
authors: ME
authors: Stockton