Inhibition of cyclic GMP hydrolysis with zaprinast reduces basal and cyclic AMP‐elevated L‐type calcium current in guinea‐pig ventricular myocytes

Abstract

1 Cyclic GMP (cGMP) has been shown to be an important modulator of cardiac contractile function. A major component of cGMP regulation of contractility is cGMP-mediated inhibition of the cardiac calcium current (I Ca ). An under-appreciated aspect of cyclic nucleotide signalling is hydrolysis of the cyclic nucleotide (i.e., breakdown by phosphodiesterases (PDEs)). The role of cGMP hydrolysis in regulating I Ca has not been studied. Thus the purpose of this study was to investigate if inhibition of cGMP hydrolysis can modulate I Ca in isolated guinea-pig ventricular myocytes. 2 Zaprinast, a selective inhibitor of cGMP-speci®c PDE (PDE5), caused a signi®cant increase in cGMP levels in myocytes, but was without a ect on basal or b-adrenergic stimulated cAMP levels (consistent with its actions as a speci®c inhibitor of PDE5). 3 Zaprinast inhibited I Ca that was pre-stimulated with cAMP elevating agents (isoproterenol, a badrenergic agonist; or forskolin, a direct activator of adenylate cyclase). The e ect of zaprinast was greatly reduced by KT5823, an inhibitor of cGMP-dependent protein kinase (PKG). 4 Zaprinast also signi®cantly inhibited basal I Ca when perforated-patch or whole-cell recording with physiological pipette calcium concentration (10 77 M) was used. However, this e ect was not observed when using standard calcium-free whole-cell recording conditions. 5 These results indicate that inhibition of cGMP hydrolysis can decrease both basal and cAMPstimulated I Ca . Thus, cGMP hydrolysis may likely be an important step for physiological modulation of I Ca . This regulation may also be important in disease states in which cGMP production is increased and PDE5 expression is altered, such as heart failure.

Relevance of Brain Natriuretic Peptide in Preload-Dependent Regulation of Cardiac Sarcoplasmic Reticulum Ca 2+ ATPase Expression

“…6 Activation of PKG-I has been shown to inhibit L-type Ca 2ϩ current. 34,35 Overexpression of PKG-I reduced cardiac myocyte Ca 2ϩ transient amplitude and resulted in impaired Ca 2ϩ /calmodulin-dependent calcineurin/ NFAT activation. 6 This reduction in Ca 2ϩ transient amplitude also could explain the mild negative inotropic effect exerted by 100 pmol/L BNP in this study.…”

Endothelial nitric oxide synthase decreases β-adrenergic responsiveness via inhibition of the L-type Ca2+ current

“…Whole cell voltage-clamp was used to measure I Ca using an Axopatch-200B amplifier and pClamp 8.1 software (Axon Instrument, Foster City, CA), as described previously (56). Electrodes (borosilicate glass tubing), with a resistance of 1.5-3 M⍀, were filled with (in mM): 120 CsCl, 6 MgCl 2, 10 EGTA, 10 HEPES, and 2 MgATP, pH 7.2 adjusted with CsOH.…”

Cyclic Guanosine Monophosphate Compartmentation in Rat Cardiac Myocytes

“…25 Second, PDE5 inhibition with the use of sildenafil (Viagra) decreases the ␤-adrenergic stimulation of cardiac systolic and diastolic function in dog, 50 mouse, 25 and human 51 as well as the ␤-stimulation of I Ca,L in guinea pig ventricular myocytes. 52 Finally, chronic exposure to sildenafil was found to prevent and reverse cardiac hypertrophy in mouse hearts exposed to sustained pressure overload. 5 With our study, we confirm the presence of functional PDE5 in ARVMs.…”