Local response of L‐type Ca²⁺ current to nitric oxide in frog ventricular myocytes

Abstract

The regulation of L‐type Ca2+ current (ICa) by the two nitric oxide (NO) donors sodium nitroprusside (SNP, 1 μm to 1 mm) and (±)‐S‐nitroso‐N‐acetylpenicillamine (SNAP, 3 or 10 μm) was investigated in frog ventricular myocytes using double voltage clamp and double‐barrelled microperfusion techniques. SNP and SNAP depressed the isoprenaline (ISO, 10‐100 nm)‐ or forskolin (FSK, 1 μm)‐mediated stimulation of ICa via cGMP activation of the cGMP‐stimulated phosphodiesterase (PDE2). Complete inhibition of the ISO (100 nm) response was observed at 1 mm SNP. When SNP was applied locally, i.e. to one‐half of the cell, and ISO to the whole cell, the response of ICa to ISO was strongly antagonized in the cell half exposed to SNP (up to 100 % inhibition at 1 mm SNP) but a relatively small depression was observed in the other half of the cell (only 20 % inhibition at 1 mm SNP). The NO scavenger 2‐(4‐carboxyphenyl)‐4,4,5,5‐tetramethylimidazoline‐1‐oxyl 3‐oxide (carboxy‐PTIO, 1 mm) reversed the local effect of SNAP (3 μm) on FSK‐stimulated ICa when applied to the same side as the NO donor, but had no effect when applied to the other side of the cell. A local application of erythro‐9‐(2‐hydroxy‐3‐nonyl)adenine (EHNA, 30 μm), a selective inhibitor of PDE2, fully reversed the local effect of SNP (100 μm) or SNAP (10 μm) on ICa but had no effect on the distant response. When EHNA was applied on the distant side, with SNP (1 mm) and ISO (100 nm) applied locally, the distant effect of SNP was fully reversed. Our results demonstrate that in frog ventricular myocytes stimulation of guanylyl cyclase by NO leads to a strong local depletion of cAMP near the L‐type Ca2+ channels due to activation of PDE2, but only to a modest reduction of cAMP in the rest of the cell. This may be explained by the existence of a tight microdomain between L‐type Ca2+ channels and PDE2.

Cardiac Nitric Oxide Synthase 1 Regulates Basal and β-Adrenergic Contractility in Murine Ventricular Myocytes

“…These data suggest that the main effect of NOS1 in intact myocytes may not be at the level of the SERCA2a but at the L-type calcium channel. This is consistent with recent work indicating that myocardial NO production can tonically inhibit the L-type calcium current in frog 17 and guinea pig 18 cardiac myocytes and is consistent with experiments showing that NOS1-derived NO suppresses voltage-sensitive calcium entry in neurons. 19 In addition, increasing consideration is being given to the notion that local concentrations of NO govern subcellular processes in microdomains.…”

Carbon monoxide activates human intestinal smooth muscle L-type Ca2+ channels through a nitric oxide-dependent mechanism

“…NO directly modulates the ␤-subunit, and CO modulates the ␣-subunit of large conductance Ca 2ϩ -activated K ϩ channels (42). NO also modulates L-type Ca 2ϩ channel activity (4,38,44). The effects of NO on L-type Ca 2ϩ channels are complex and tissue dependent.…”

Cyclic Guanosine Monophosphate Compartmentation in Rat Cardiac Myocytes

“…For instance, in primary bovine glomerulosa cells, PDE2 is the main enzyme by which ANP inhibits aldosterone secretion, 43 and this is achieved by a marked reduction in cAMP level due to cGMP activation of PDE2. 43 In frog ventricular 26,33,41 and human atrial myocytes, 44,45 NO donors or intracellular cGMP induces activation of PDE2, causing a decrease in cAMP and an inhibition of I Ca,L . 29 Our study demonstrates that PDE2 is also an important component of the cGMP catabolism in cardiomyocytes.…”

“…25 Previous work from this laboratory has examined the response of cardiac L-type Ca 2ϩ channels to a local application of NO donors and demonstrated a rather limited spread of intracellular cGMP from its site of production to the remote part of the cell not exposed to NO, where sGC was inactive. 26 In this study our aim was to characterize and compare in real time the changes in subsarcolemmal cGMP concentration in response to activators of sGC and pGC. For that purpose, we used the wild-type (WT) ␣-subunit of the rat olfactory cyclic nucleotide-gated channel (CNGA2) as a real-time sensor for subsarcolemmal cGMP.…”