Multiple conductance states of single Ca2+-activated Clâ channels in rabbit pulmonary artery smooth muscle cells
Ca 2+ -activated Cl â 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 â channels in freshly dispersed rabbit pulmonary artery myocytes. In the c...
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Published in | The Journal of physiology Vol. 547; no. 1; p. 181 |
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Main Authors | , |
Format | Journal Article |
Language | English |
Published |
The Physiological Society
15.02.2003
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Online Access | Get full text |
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Summary: | Ca 2+ -activated Cl â 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 â 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 â channels opened either to the 1.8 pS or 1.2 pS level. In 0 [Ca 2+ ] i , no channel activity was observed at â100 mV to +100 mV, but with 10â250 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 â100 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 â by I â shifted the reversal potential by about â30 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 â channels is proposed. |
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ISSN: | 0022-3751 1469-7793 |
DOI: | 10.1113/jphysiol.2002.033688 |