Direct effect of Ca 2+ –calmodulin on cGMP‐activated Ca 2+ ‐dependent Cl − channels in rat mesenteric artery myocytes
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 patch...
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Published in | The Journal of physiology Vol. 559; no. 2; pp. 449 - 457 |
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Main Authors | , |
Format | Journal Article |
Language | English |
Published |
01.09.2004
|
Online Access | Get full text |
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Summary: | 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. |
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ISSN: | 0022-3751 1469-7793 |
DOI: | 10.1113/jphysiol.2004.070045 |