Electrophysiological, mechanosensitive responses of Xenopus laevis oocytes to direct, isotonic increase in intracellular volume.

An intra-oocyte injection method for obtaining the electrophysiological response of follicle-enclosed Xenopus laevis oocytes to an increase in intracellular volume (i.e. stretch) without changing the extracellular medium is described. The response comprised a 'stretch-activated' (SA) current which was evoked by injection of an isotonic 14-70 nl droplet and had a transient, smooth profile. Ionic substitution experiments revealed that the current was carried mainly by Na(+), K(+) and Cl(-) and had a reversal potential of about -2 mV. A similar result was obtained from experiments in which the holding potential was varied between -40 and +10 mV whilst repeatedly inducing the SA current. On average, the channel was blocked 60% by 10 microM gadolinium chloride, 58% by 50 microM amiloride, 11% by 50 microM 4,4'-diisothiocyanatostilbene-2, 2'-disulfonic acid and 63% by 50 microM 4-acetamido-4'-isothiocyanato-stilbene-2-2'-disulfonic acid. Maturation of the oocytes with 100 microM progesterone reduced the mechanosensitivity 12-fold. This injection technique is compared with other methods of eliciting mechanosensitive (MS) currents in X. laevis oocytes. These observed characteristics of the SA current are discussed in relation to the oocytes' endogenous MS cation and anion channels.