An improved loose patch voltage clamp method using concentric pipettes

A method for noninvasive voltage-clamp recording from large cells is described. A firepolished pipette having two concentric barrels is pushed against the cell membrane, thereby electrically isolating a circular patch subdivided into an inner and an annular outer region. Both regions are held isopotential, but current is collected from the inner region only. The method electrically simulates a high resistance seal between pipette and cell membrane, allowing accurate and rapid voltage-clamp recording under conditions where the seal resistances actually obtained are low (near 1 MΩ). This is useful in applications where one wishes to avoid enzymatic treatment. We provide details of electrode construction and voltage-clamp electronics, and present results obtained from frog skeletal muscle and leech neurons. For sodium channels of frog muscle, extensive data were previously obtained with other methods. There is good agreement between the earlier results and the measurements presented here.