Direct effect of Ca2+–calmodulin on cGMP-activated Ca2+-dependent Cl−channels in rat mesenteric artery myocytes

• Published in: The Journal of physiology Vol. 559; no. 2; p. 449
• Main Authors: A. S. Piper, W. A. Large
• Format: Journal Article
• Language: English
• Published: The Physiological Society 01.09.2004
• ISSN: 0022-3751; 1469-7793
• DOI: 10.1113/jphysiol.2004.070045

Recently a novel cGMP-activated Ca 2+ -dependent Cl − channel has been described in rat mesenteric artery smooth muscle cells. In the present work we have investigated the actions of calmodulin (CaM) on single channel cGMP-activated Ca 2+ -dependent Cl − current ( I Cl(cGMP,Ca) ) in inside-out patches. When 1 μ m CaM was applied to the intracellular surface of inside-out patches bathed with 10 μ m cGMP and 100 n m [Ca 2+ ] i there was approximately a 10-fold increase in channel open probability ( NP o ). This effect of CaM was not observed with lower [Ca 2+ ] i and 100 n m [Ca 2+ ] i with 1 μ m CaM did not activate Cl − channels in the absence of cGMP. The unitary conductance, reversal potential and mean open time of the single-channel currents were similar in the absence or presence of CaM. With 10 μ m cGMP and 100 n m [Ca 2+ ] i the relationship between NP o and CaM concentration was well fitted by the Hill equation yielding an equilibrium constant for CaM of about 1.9 n m and a Hill coefficient of 1.7. With 1 μ m CaM (+10 μ m cGMP) the relationship between [Ca 2+ ] i and NP o was also fitted by the Hill equation which yielded an apparent equilibrium constant of 74 n m [Ca 2+ ] i and a Hill coefficient of 4.8. When [Ca 2+ ] i was increased from 300 n m to 1 μ m there was a decrease in NP o . The potentiating effect of CaM was markedly reduced by the selective CaM binding peptide Trp (5 n m ) but not by the Ca 2+ /CaM-dependent protein kinase II (CaMKII) inhibitor autocamtide II related inhibitory peptide (AIP). It is concluded that CaM potentiates the activity of single channel I Cl(cGMP,Ca) by increasing the probability of channel opening via a CaMKII-independent mechanism.