Influence of sodium-calcium exchange on calcium current rundown and the duration of calcium-dependent chloride currents in pituitary cells, studied with whole cell and perforated patch recording.

Abstract

The whole cell patch-clamp technique, in both standard and perforated patch configurations, was used to study the influence of Na+-Ca ++ exchange on rundown of voltage-gated Ca ++ currents and on the duration of tail currents mediated by Ca § CI-channels. Ca §247 currents were studied in GH3 pituitary cells; Ca++-dependent CI-currents were studied in AtT-20 pituitary cells. Na+-Ca ++ exchange was inhibited by substitution of tetraethylammonium (TEA +) or tetramethylammonium (TMA +) for extracellular Na § Control experiments demonstrated that substitution of TEA § for Na § did not produce its effects via a direct interaction with Ca+ +-dependent CI-channels or via blockade of Na+-H + exchange. When studied with standard whole cell methods, Ca § § and Ca + +-dependent C1-currents ran down within 5-20 min. Rundown was accelerated by inhibition of Na+-Ca + § exchange. In contrast, the amplitude of both Ca + § and Ca § dependent CI-currents remained stable for 30-150 min when the perforated patch method was used. Inhibition of Na § § exchange within the first 30 min of perforated patch recording did not cause rundown. The rate of Ca+ § dent CI-current deactivation also remained stable for up to 70 min in perforated patch experiments, which suggests that endogenous Ca + § buffering mechanisms remained stable. The duration of Ca §247 CI-currents was positively correlated with the amount of Ca + § influx through voltage-gated Ca § channels, and was prolonged by inhibition of Na § §247 exchange. The influence of Na+-Ca ++ exchange on CI-currents was greater for larger currents, which were produced by greater influx of Ca §247 . Regardless of Ca §247 influx, however, the prolongation of Cl-tail currents that resulted from inhibition of Na+-Ca + § exchange was modest. Tail currents were prolonged within tens to hundreds of milliseconds of switching from Na § to TEA+-containing bath solutions.

Myosin II Activation and Actin Reorganization Regulate the Mode of Quantal Exocytosis in Mouse Adrenal Chromaffin Cells

“…All electrophysiological recordings were performed in the perforated-patch configuration (Korn and Horn, 1989) as previously described (Chan and Smith, 2001), with some modifications described here. The electrical stimulus protocols were delivered by either an EPC-9 or an EPC-10 amplifier (HEKA Elektronik, Lambrecht, Germany) controlled by Pulse (HEKA Elektronik; version 8.8).…”

Clonidine inhibits ATP‐sensitive K+channels in mouse pancreatic β‐cells

“…Clonidine had no effect on the leakage current (data not shown). (Horn & Marty, 1988;Korn & Horn, 1989;Falke et al, 1989;Smith et , 1989). With this method calcium currents were much more stable than with the conventional whole cell technique (Plant, 1988), but did show a slow run-down in some cells.…”

Acetylcholine activates non‐selective cation and chloride conductances in canine and guinea‐pig tracheal myocytes.

“…Using the nystatin perforated patch technique (Horn & Marty, 1988;Korn & Horn, 1989), we investigated the effects of ACh on single cells enzymatically dispersed from canine and guinea-pig trachealis. Our objectives were to investigate the membrane conductance changes that accompany cholinergic stimulation.…”