Block of Stretch-Activated Ion Channels in Xenopus Oocytes by Gadolinium and Calcium Ions

Gadolinium ions produce three distinct kinds of block of the stretch-activated (SA) ion channels in Xenopus oocytes: a concentration-dependent reduction in channel open time, a concentration-dependent reduction in open channel current, and a unique, steeply concentration-dependent, reversible inhibition of channel opening. This last effect reduces the probability of a channel being open from about 10(-1) at 5 microM to less than 10(-5) at 10 microM gadolinium. Calcium has effects on open time and current similar to that of gadolinium, but this channel is permeable to calcium and calcium does not completely inhibit channel activity. The availability of a blocker for SA ion channels may help to define their physiological function, and will simplify the use of oocytes as an expression system for ion channels.