Spontaneous single-channel activity of neuronal TRP5 channel recombinantly expressed in HEK293 cells

Mammalian homologues of the Drosophila transient receptor potential (trp) protein (TRP) form Ca(2+) permeable cation channels activated in response to stimulation of G-protein-coupled receptors. Establishing biophysical characteristics of basal TRP activity is of great importance in understanding modulatory processes, which underlie enhancement of TRP activity via receptor stimulation. We have examined spontaneous activity of the TRP5 channel recombinantly expressed in human embryonic kidney cells, using the conventional whole-cell mode of the patch-clamp technique in a low-Ca(2+) external solution. The unitary Na(+) conductance of the TRP5 channel was linear, being 47.6 pS. By contrast, the open probability of the TRP5 channel showed a voltage-dependent decrease below -50 mV. These biophysical properties are important hallmarks in distinguishing the TRP5 channel in native neuronal preparations, whose spontaneous activity may contribute to control of resting membrane potentials and generation of action potentials.