Multiple conductance states of single Ca2+-activated Cl− channels in rabbit pulmonary artery smooth muscle cells

• Published in: The Journal of physiology Vol. 547; no. 1; p. 181
• Main Authors: A S Piper, W A Large
• Format: Journal Article
• Language: English
• Published: The Physiological Society 15.02.2003
• ISSN: 0022-3751; 1469-7793
• DOI: 10.1113/jphysiol.2002.033688

Ca 2+ -activated Cl − channels contribute to agonist-evoked contraction and spontaneous activity in some smooth muscle preparations. Patch pipette techniques were used to study the properties of single Ca 2+ -activated Cl − channels in freshly dispersed rabbit pulmonary artery myocytes. In the cell-attached recording mode, two conductance states of 3.5 and 1.8 pS were recorded either spontaneously or in response to increasing [Ca 2+ ] i . With inside-out patches, the 3.5 pS channel current predominated at 50 n m [Ca 2+ ] i , but at 500 n m [Ca 2+ ] i most channels opened to the 1.8 pS level and an additional 1.2 pS channel conductance was resolved. At 1 µ m [Ca 2+ ] i all of the Cl − channels opened either to the 1.8 pS or 1.2 pS level. In 0 [Ca 2+ ] i , no channel activity was observed at −100 mV to +100 mV, but with 10–250 n m [Ca 2+ ] i the total single channel open probability (N P o ) increased with depolarisation. This voltage dependence was not seen at higher values of [Ca 2+ ] i . The plot of N P o vs. [Ca 2+ ] i yielded Ca 2+ affinity constants of 8 and 250 n m and Hill slopes of 1.3 and 2.3 at +100 and −100 mV, respectively. The distribution of open times was fitted by two exponentials of about 5 and 30 ms, which were neither voltage nor Ca 2+ dependent. Replacement of external Cl − by I − shifted the reversal potential by about −30 mV and lengthened the longer of the two mean open times without significant effects on other kinetic parameters. Based on these data, a model for the activation of Ca 2+ -activated Cl − channels is proposed.