Characterization of whole-cell currents elicited by mechanical stimulation of Xenopus oocytes.

Whole-cell mechanosensitive current (I(ms)) in Xenopus oocytes was studied using the two-electrode voltage-clamp technique. I(ms) was evoked by mechanically pressing the oocyte surface with a glass micropipette. The current was found to depend on the amplitude of the stimulus, showed a time-dependent decay, and turned off immediately after the stimulus was removed. The current-voltage relationship for the peak current exhibited inward and outward rectification at negative and positive potentials, respectively, while that for the sustained current exhibited only inward rectification. I(ms) was significantly suppressed by 30 microM Gd3+. One millimolar amiloride also significantly suppressed the inward I(ms) at negative potentials, but not the outward one at positive potentials. Replacing extracellular Na+ with K+ did not change the current-voltage relationship, whereas replacing extracellular Na+ with choline+ or tetraethylammonium+ significantly decreased the inward I(ms). The outward rectifier at positive potentials was abolished by replacing extracellular Cl- with gluconate-, by intracellular injection of 1,2-bis (2-aminophenoxy) ethane-N,N,N',N'-tetraacetic acid (BAPTA), by extracellular application of anthracene-9-carboxylic acid, and by replacing extracellular Ca2+ with Mg2+. These results suggest that mechanical stimulation activates stretch-activated cation channels and Ca2+-activated Cl- channels, the latter being secondarily activated by an increase in intracellular Ca2+ concentration by Ca2+ influx through stretch-activated cation channels.