Nitric oxide regulates the calcium current in isolated human atrial myocytes.

Abstract

Cardiac Ca2+ current (I") was shown to be regulated by cGMP in a number of different species. Recently, we found that the NO-donor SIN-1 (3-morpholino-sydnonimine) exerts a dual regulation of Ic. in frog ventricular myocytes via an accumulation of cGMP. To examine whether NO also regulates Ca2" channels in human heart, we investigated the effects of SIN-1 on Ic. in isolated human atrial myocytes.An extracellular application of SIN-1 produced a profound stimulatory effect on basal IC. at concentrations > 1 pM.Indeed, 10 pM SIN-1 induced a s 35% increase in Ic.. The stimulatory effect of SIN-1 was maximal at 1 nM ( z 2-fold increase in ICa) and was comparable with the effect of a saturating concentration (1 ,uM) of isoprenaline, a 13-adrenergic agonist. Increasing the concentration of SIN-1 to 1-100 ,uM reduced the stimulatory effect in two thirds of the cells. The stimulatory effect of SIN-1 was not mimicked by SIN-1C, the cleavage product of SIN-1 produced after liberation of NO. This suggests that NO mediates the effects of SIN-1 on ICa. Because, in frog heart, the stimulatory effect of SIN-1 on Ic. was found to be due to cGMP-induced inhibition of cGMP-inhibited phosphodiesterase (cGI-PDE), we compared the effects of SIN-1 and milrinone, a cGI-PDE selective inhibitor, on Ic. in human. Milrinone (10 ,uM) induced a strong stimulation of 'Ca (-150%), demonstrating that cGI-PDE controls the amplitude of basal Ic. in this tissue. In the presence of milrinone, SIN-1 (0.1-1 nM) had no stimulatory effect on ICa, suggesting that the effects of SIN-1 and MIL were not additive. We conclude that NO may stimulate ICa in human atrial myocytes via inhibition

Characterization of the cyclic nucleotide phosphodiesterase subtypes involved in the regulation of the L‐type Ca2+ current in rat ventricular myocytes

“…The maximal amplitude of I Ca was measured as the di erence between the peak inward current and the end-pulse current (I 200 or I 400 ), which was the current amplitude at the end of the 200 or 400 ms duration pulse (Kirstein et al, 1995). Currents were not compensated for capacitive and leak currents.…”

“…For this reason, selective PDE inhibitors, such as EHNA or milrinone, have no e ect on basal I Ca in frog myocytes (Fischmeister & Hartzell, 1990;Me ry et al, 1995) while they do stimulate basal I Ca in human atrial myocytes (Kirstein et al, 1995;Kajimoto et al, 1997;Rivet-Bastide et al, 1997). Similarly, PDE3 inhibitors stimulate basal I Ca in rabbit cardiomyocytes (Kajimoto et al, 1997) and exert a positive inotropic e ect in guinea-pig left atria (Muller et al, 1990).…”

“…Potassium currents were blocked by replacing all K + ions with intracellular and extracellular Cs + . For the determination of current-voltage relationships for I Ca (see Figure 4A) and I Ca inactivation curve (see Figure 4B), a double pulse voltage clamp protocol was used (Kirstein et al, 1995). Brie¯y, every 4 s, the membrane potential of the cell, which was normally maintained at its holding value of 750 mV, experienced the following sequence of events: 750 mV for 10 ms, di erent potentials values ranging from 7100 to +100 mV for 200 ms, 750 mV for 3 ms, and 0 mV for 200 ms (see inset in Figure 4B).…”

“…Erythro-9-[2-Hydroxy-3-nonyl]adenine (EHNA), a selective PDE2 inhibitor (Me ry et al, 1995;Podzuweit et al, 1995), stimulates basal I Ca in human atrial cells (Rivet-Bastide et al, 1997), and antagonizes the inhibitory e ect of intracellular cyclic GMP or NO-donors on isoprenaline-or cyclic AMP-stimulated I Ca in frog ventricular myocytes (Me ry et al, 1995). Inhibition of PDE3 with milrinone results in an increase in basal I Ca in human atrial myocytes (Kirstein et al, 1995). Similarly, application of intracellular cyclic GMP in guinea-pig ventricular (Shiriyama & Pappano, 1996;Ono & Trautwein, 1991) or human atrial myocytes (Rivet-Bastide et al, 1997) or activation of guanylyl cyclase by NO donors in human atrial myocytes (Kirstein et al, 1995) leads to an increase in I Ca mediated by cyclic GMP inhibition of PDE3.…”

“…Inhibition of PDE3 with milrinone results in an increase in basal I Ca in human atrial myocytes (Kirstein et al, 1995). Similarly, application of intracellular cyclic GMP in guinea-pig ventricular (Shiriyama & Pappano, 1996;Ono & Trautwein, 1991) or human atrial myocytes (Rivet-Bastide et al, 1997) or activation of guanylyl cyclase by NO donors in human atrial myocytes (Kirstein et al, 1995) leads to an increase in I Ca mediated by cyclic GMP inhibition of PDE3. Ro20-1724 or rolipram, two selective PDE4 inhibitors, enhance the response of I Ca to cyclic AMP, isoprenaline or forskolin in frog cardiomyocytes (Fischmeister & Hartzell, 1990;Me ry et al, 1995).…”