Effects of Rmi 12330a, a New Inhibitor of Adenylate Cyclase on Myocardial Function and Subcellular Activity

Abstract

RMI 12330A, a lactam‐imine, at concentrations of 10−4 m and higher, inhibited basal as well as isoprenaline and NaF‐stimulated adenylate cyclase activity of guinea‐pig heart homogenates. However, RMI 12330A was a more potent inhibitor of histamine‐stimulated adenylate cyclase (IC50 of 1.5 × 10−5 m). In the isolated work‐performing heart of the guinea‐pig, RMI 12330A (IC50 of 1.1 × 10−6 m) depressed all cardiac functions: pressures developed, dP/dt, contractile force, dF/dt, work performance and stroke work. Left atrial pressure rose and the positive inotropic response to increasing heart rate (staircase) became negative. Histamine, isoprenaline and ouabain no longer caused positive inotropic effects. Increasing the perfusate calcium concentration from 2.5 mm to 4.5 and 6.5 mm completely restored cardiac function after its depression by RMI 12330A. RMI 12330A uncoupled mitochondrial oxidative phosphorylation; the classical uncoupler, dinitrophenol, had the same effects on cardiac dynamics as RMI 12330A. RMI in high doses inhibited hydrolytic activity of Na+, K+‐ATPase of crude and purified heart preparations (IC50 of 1.7 × 10−4 m) and inhibited ouabain binding to the same enzymes (IC50 of 1.5 × 10−4 m). A lactam‐imine analogue of RMI 12330A that had no effect on adenylate cyclase, was also without effect on any of the systems examined.

Ca2+ Entry Mediated by Store Depletion,S-Nitrosylation, and TRP3 Channels

“…Our previous work indicated that the NO donor was functioning independently of cyclic GMP (23). In evaluating the possible involvement of cyclic AMP we utilized a number of different adenylyl cyclase modifiers including the cycloalkyl lactamamide, MDL-12330A, which has been utilized widely as an irreversible adenylyl cyclase inhibitor (35)(36)(37). Surprisingly, as shown in Fig.…”

Parallel pathways mediate inhibitory effects of vasoactive intestinal polypeptide and nitric oxide in canine fundus

“…cis ‐ N ‐ (2 ‐ phenylcyclopentil) ‐ azacyclotridec ‐ 1en ‐2‐amine monohydrochloride (MDL 12,330A) has been shown to block adenylyl cyclase in numerous preparations (e.g. Grupp et al ., 1980 ; Satake et al ., 1996 ). Addition of MDL 12,330A (50 μ M ) caused an increase in tone (to 235±34% of the basal level) ( n =18), suggesting ongoing production of cyclic GMP in these muscles (Figure 6).…”

Pharmacological Distinction between Soluble and Transmembrane Adenylyl Cyclases

“…Among adenylyl cyclase inhibitors, the original report identifying MDL-12,330a described an adenylyl cyclase-independent effect on the Na 1 , K 1 -ATPase (Grupp et al, 1980), and a more recent study identified an off-target effect on glycine transport (Gadea et al, 1999). As these inhibitors are used more widely, nonspecific effects become appreciated; for example, a recent report found that SQ22,536 has an effect on ERK activation unrelated to cAMP signaling (Emery et al, 2013), and two recent reports described sAC-independent effects of KH7 (Tian et al, 2011;Di Benedetto et al, 2013).…”