Effects of KT-362, a sarcolemmal and intracellular calcium antagonist, on calcium transients of cultured neonatal rat ventricular cells: A comparison with gallopamil and ryanodine

Abstract

We evaluated the effects of KT-362 (5-[3-([2-(3,4-dimethoxyphenyl)-ethyl]amino)-1-oxopropyl]-2,3,4,5, -tetrahydro-1,5-benzothiazepine fumarate), a putative intracellular calcium antagonist, on the intracellular free calcium concentration ([Ca2+]i) of cultured neonatal rat ventricular cells using microfluorometry of fura-2. The effects were compared with those of gallopamil (D-600), a sarcolemmal calcium channel antagonist, and ryanodine, a modulator of sarcoplasmic reticulum (SR) function. KT-362 decreased both systolic [Ca2+]i (sCa) and diastolic [Ca2+]i (dCa) in cell aggregates, in a concentration (1, 3, 10, and 30 microM) and stimulation frequency (0.2, 0.5, and 1.0 Hz) dependent manner. The time to peak of the Ca2+ transient was significantly prolonged by KT-362 at a concentration of 30 microM, while the half-life of the Ca2+ transient was prolonged at concentrations of > or = 10 microM. Gallopamil (1 microM) decreased both sCa and dCa in a frequency (0.2, 0.5, and 1.0 Hz) dependent fashion, as was the case for KT-362, but did not change the time course of Ca2+ transients. Ryanodine (10 microM) prolonged the time to peak and half-life of the Ca2+ transient, as was also the case for KT-362, while the effect of ryanodine on dCa differed from that of KT-362. Finally, the effect of KT-362 on Ca2+ transients could be mimicked by simultaneous application of gallopamil and ryanodine. These results suggest that KT-362 is a novel compound that exerts depressant effects on both sarcolemmal Ca2+ channels, and perhaps Ca2+ release channels of the sarcoplasmic reticulum, in cultured neonatal rat ventricular cells.

CGP-37157 Inhibits the Sarcoplasmic Reticulum Ca2+ATPase and Activates Ryanodine Receptor Channels in Striated Muscle

“…Reports have suggested that this compound can affect plasmalemma NCX (Czyz and Kiedrowski, 2003) and L-type Ca 2ϩ channels (Thu et al, 2006). Various benzothiazepines with relatively different side chains, such as K201 (Kohno et al, 2003;Hunt et al, 2007) and KN-362 (Kodama et al, 1988;Tatsukawa and Arita, 1997), are known to modulate RyRs. K201 was also found to block the SERCA (Loughrey et al, 2007).…”

Class IV Antiarrhythmic Agents: New Compounds Using an Old Strategy

“…30 µM KT-362 increased time to peak of the Ca 2+ transient, while the half-life of the calcium transient was prolonged at 10 µM and above. These effects of KT-362 on Ca 2+ transients could be mimicked by simultaneous application of 1 µM D600 and 10 µM ryanodine, suggesting that KT-362 inhibits both sarcolemmal calcium channels and calcium release channels of the sarcoplasmic reticulum [105]. Other studies also support the inhibition of calcium release channels of the endoplasmic reticulum (inositol-triphosphate receptor) by KT-362 in the micromolar range in rabbit aorta [191] and in canine femoral arteries [192].…”

“…The other one is the calcium content of the intracellular calcium stores not to mention the sarcoplasmic reticulum gain which relates the amount of released calcium to the amount of the triggering calcium [101], [102]. These two factors are both reduced by CCAs, therefore it is not surprising that CCAs lead to the decrease of calcium transient amplitudes (for verapamil and mibefradil [103] for D600 [104], for SR33805 [40], for KT-362 [105] and for AH-1058 [106]). The major ATP using process in myocytes is the contractile machinery, the activity of which depends on intracellular calcium.…”