A CALCIUM-ACTIVATED, LARGE-CONDUCTANCE AND NONSELECTIVE CATION CHANNEL IN PARAMECIUM CELL

A non-selective cation channel was found in mutant Paramecium cells (K 115). This cell had been selected as a resistant mutant in a high-K+ s olution. In patch clamp studies of these cells in the inside-out confi guration, this channel was activated by bath applications of elevated Ca2+ concentrations. The channels became very active when the Ca2+ con centration was above 3.2 mu M. The channel was also activated by depol arization. The voltage dependency was steep upon depolarization, where as upon hyperpolarization the channel activity barely changed. This ch annel had poor selectivity for monovalent alkali cations. Using the Go ldman-Hodgkin-Katz equation for the reversal potential, the permeabili ty ratios with respect to K+ for Na+, Rb+, Cs+ and Li+ were nearly 1. Although the permeability ratios were similar for each cation, the sin gle channel conductances differed. The single channel conductances wer e 467 pS with K+ as the charge carrier, 406 pS with Na+, 397 pS with R b+, 253 pS with Cs+ and 198 pS with Li+ upon depolarization in 100 mM cation solutions. A similar calcium-activated large conductance channe l was observed in the wild-type (G3) Paramecium cells but was very rar e. (C) 1997 Elsevier Science B.V.