Membrane patch and whole cell response of Xenopus oocytes to mechanical, electrical and osmotic stimulation.

摘要

Mechano-gated (MG) channels have been found in almost all cell types tested. However, in most cases their cellular functions remains unknown. A major hindrance in understanding the function of MG channels in nonspecialized cells has been the failure to demonstrate a whole cell mechanosensitive current that could be related to specific MG channel activity. The MG channel in Xenopus oocytes is one of the best characterized single MG channels but a whole cell MG current has not yet been demonstrated. In this study, attempts are made to evoke the whole cell MG currents in Xenopus oocytes. These attempts are based on the single channel properties of this channel, namely, its block by extracellular Ca2+, its voltage dependent gating and its mechanosensitivity. A variety of methods have been applied to activate a whole cell MG current, including removal of extracellular Ca2+, hyperpolarization/depolarization, osmotic stress, and direct mechanical stimulation.;The difference in ion selectivity, pore size, pharmacology and Cx38 antisense sensitivity indicates that the extracellular Ca2+ inactivated whole cell conductance (Ic) is not mediated by the MG channel but instead a hemigap junctional channel. Strong hyperpolarization and hypertonicity each activated a novel whole cell conductance but they could not be related to the MG channel. Depolarization activated a non-selective conductance that differs from the MG channel in ionselectivity and sensitivity to flufenamic acid. Direct mechanical stimulation including cell inflation, suction through macropipettes, fluid ejection and direct prodding of the oocytes also failed to evoke whole cell MG current responses. Possible explanations for the discrepancy between the predicted and the recorded whole cell MG currents, including difference between whole cell voltage-clamp and patch-clamp recordings (cytoskeleton-channel interactions and the effect of the vitelline membrane) and release of membrane tension by membrane folding and/or membrane recruitment were explored and discussed in this study.