Single cGMP-activated Ca2+-dependent Cl- channels in rat mesenteric artery smooth muscle cells

• Published in: The Journal of physiology Vol. 555; no. 2; pp. 397 - 408
• Main Authors: Piper, A. S., Large, W. A.
• Format: Journal Article
• Language: English
• Published: 9600 Garsington Road , Oxford , OX4 2DQ , UK The Physiological Society 01.03.2004; Blackwell Publishing Ltd; Blackwell Science Inc
• Subjects: Research Papers
• ISSN: 0022-3751; 1469-7793
• DOI: 10.1113/jphysiol.2003.057646

The present study describes the single channel properties of a novel cGMP-activated Ca 2+ -dependent Cl − channel in rat mesenteric artery smooth muscle cells. Single channel currents were recorded in cell-attached patches in the presence of 8Br cGMP in response to the addition of caffeine or noradrenaline and in both outside-out and inside-out patches when the internal patch surface was bathed in cGMP and Ca 2+ . The channels were permeable to Cl − ions with an anion permeability sequence of SCN − (1.7) > Cl − (1.0) > I − (0.6). Single channel mean open probability ( NP o ) was independent of voltage and the channels displayed three conductance levels of 15, 35 and 55 pS. cGMP was required for channel activation and the single channel NP o increased sharply with raised [Ca 2+ ] i , maximal activation occurring at a [Ca 2+ ] i of about 100 n m . The relationship between NP o and cGMP concentration was voltage independent and could be fitted by the Hill equation giving a K d of about 3 μ m and a Hill coefficient ( n H ) of 3. cGMP- and Ca 2+ -dependent channel currents were inhibited by 10 μ m ZnCl 2 but niflumic acid, an inhibitor of Ca 2+ -activated Cl − channels, had no effect. Inhibition of cGMP-dependent protein kinase activity by the cGMP-dependent protein kinase inhibitor KT5823 or replacement of ATP by AMP-PNP reduced NP o , while activation of cGMP-dependent protein kinase by guanosine 3′, 5′-cyclic monophosphate, β-phenyl-1, N 2 -etheno-8-bromo-sodium salt (8Br PET cGMP) produced a significant increase in single channel NP o . It is likely that these single channel currents underlie the noradrenaline-activated inward current important for vasomotion in these resistance arteries.