Abstract
Modulation of smooth muscle, L-type Ca(2+) channels (class C, Ca(V)1.2b) by thionitrite S-nitrosoglutathione (GSNO) was investigated in the human embryonic kidney 293 expression system at the level of whole-cell and single-channel currents. Extracellular administration of GSNO (2 mM) rapidly reduced whole-cell Ba(2+) currents through channels derived either by expression of alpha1C-b or by coexpression of alpha1C-b plus beta2a and alpha2-delta. The non-thiol nitric oxide (NO) donors 2,2-diethyl-1-nitroso-oxhydrazin (2 mM) and 3-morpholinosydnonimine-hydrochloride (2 mM), which elevated cellular cGMP levels to a similar extent as GSNO, failed to affect Ba(2+) currents significantly. Intracellular administration of copper ions, which promote decomposition of the thionitrite, antagonized its inhibitory effect, and loading of cells with high concentrations of dithiothreitol (2 mM) prevented the effect of GSNO on alpha1C-b channels. Intracellular loading of cells with oxidized glutathione (2 mM) affected neither alpha1C-b channel function nor their modulation by GSNO. Analysis of single-channel behavior revealed that GSNO inhibited Ca(2+) channels mainly by reducing open probability. The development of GSNO-induced inhibition was associated with the transient occurrence of a reduced conductance state of the channel. Our results demonstrate that GSNO modulates the alpha1 subunit of smooth muscle L-type Ca(2+) channels by an intracellular mechanism that is independent of NO release and stimulation of guanylyl cyclase. We suggest S-nitrosation of intracellularly located sulfhydryl groups as an important determinant of Ca(2+) channel gating and conductance.
Highlights
The identification of nitric oxide (NO)1 as the major endothelium-derived relaxing factor led to the discovery of a variety of NO-mediated signal transduction mechanisms [1,2,3,4]
Our results demonstrate that GSNO modulates the ␣1 subunit of smooth muscle L-type Ca2؉ channels by an intracellular mechanism that is independent of NO release and stimulation of guanylyl cyclase
Channels comprised of ␣1C-b, 2a, and ␣2-␦, corresponding to channel complexes expressed in cardiovascular tissues [21, 22], were rapidly inhibited by GSNO (n ϭ 5; see Fig. 2) but barely affected by DEA/NO or SIN-1
Summary
The identification of nitric oxide (NO)1 as the major endothelium-derived relaxing factor led to the discovery of a variety of NO-mediated signal transduction mechanisms [1,2,3,4]. Inhibitory Modulation by GSNO of Class C, L-type Ca2ϩ Channels Is Associated with a Reduction of Open Probability and the Occurrence of a Reduced Conductance State—Inhibition by GSNO of ␣1C-b channels was confirmed in singlechannel recordings, using the cell-attached configuration (Fig. 6).
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