Sodium conductance in calcium channels of single smooth muscle cells of guinea-pig taenia caeci.

During the last few years, the Ca 2+-channels in isolated smooth muscle cells have been intensively studied (Walsh and Singer 1981; Bury et al. 1982; Klock­ ner and Isenberg 1985; Droogmans and Callewaert 1986). It was shown that under physiological conditions Ca 2+-channels are not measurably permeable for Na-ions (Klockner and Isenberg 1985). On the other hand, inward currents carried by Na + through Ca 2 +-channels have been detected in a variety of excitable tissues after removing external Ca 2+ by calcium chelators, such as EDTA and EGTA (neurons: Kostyuk et al. This procedure could be used to study some of the properties of Ca 2+-channels (Kostyuk et al. 1983). In investigating Na A-conductivity in single smooth muscle cells of guinea-pig taenia caeci, we obtained data concerning the inactivation of Ca 2+-channels and the role of Ca 2+ in this process. Preliminary results of these studies have already been published (Bonev and Boev 1989). Single smooth muscle cells were isolated from guinea-pig taenia caeci. Whole cell currents were studied by the patch-clamp technique (Hamill et al. 1981) using a List-electronic (EPC-7) patch-clamp amplifier. Patch pipettes with resistances ranging between 1.5—2 MÍ2 were made of Pyrex glass (Jencons H 15/10). The solutions used were of the following composition: (in mmol/1).