Patch-Clamp Recording of Ion Channels: Interfering Effects of Patch Pipette Glass

Abstract

Glass for pipettes used to record ion channel activity with the patch-clamp technique is selected on the basis of its electrical, thermal, and sealing properties. Recent findings stress a new characteristic to consider: the effect of pipette glass itself on ion channel properties.

A look at membrane patches with a scanning force microscope

“…Attachment of the membrane to the pipette glass One question often raised when patch clamp techniques are used is: how are membranes fixed to the glass of the pipette to form the high resistance "seals" (GQ-seal) (Milton et al, 1990;Zuazaga et al, 1990)? Fig.…”

Membrane-Pipette Interactions Underlie Delayed Voltage Activation of Mechanosensitive Channels in Xenopus Oocytes

“…In 18 of 18 inside-out patches formed with soft glass pipettes that contained MS channels, as verified by pressure activation, depolarization did not activate the MS channels present in the patch. The lack of depolarization-induced activation of MS channels when patches were formed of soft glass was unlikely to arise from the possible effects of divalent or multivalent cations released by the soft glass (Cota and Armstrong, 1988;Furman and Tanaka, 1988;Zuazaga and Steinacker, 1990;Copollo et al, 1991), since the solutions contained EGTA (2-10 mM, and in some experiments also 10 mM BAPTA), which would chelate these cations. Fig.…”

“…The finding that delayed cooperative activation of MS channels by voltage in the absence of stretch was observed only in patched membranes of a specific configuration formed with a particular type of glass pipette suggests that the delayed cooperative activation of MS channels by voltage is not an intrinsic property of the channels, but requires interactions between the patch of membrane and the patch pipette. Patch electrode glass is known to release ions that can influence ion channel behavior (Cota and Armstrong, 1988;Furman and Tanaka, 1988;Zuazaga and Steinacker, 1990;Copollo et al, 1991). The release of such ions from the glass does not appear to account for the different results with borosilicate and soft glass pipettes, because similar findings were obtained when high concentrations of chelators were included in the pipette solutions.…”

Application of Patch Clamp Methods to the Study of Calcium Currents and Calcium Channels

“…The inactivation was suggested to result from channel block by di-or multivalent ions leeching from the glass. Zuazaga and Steinacker (1990) also reported variations in channel behavior attributable to differences in glass type, as observed in studies of acetylcholine-gated channels in patches from Xenopus myocytes. In this case, hard glass pipettes caused the preferential dropout of 40 pS channels compared with 60 pS channels.…”