The isoquinoline derivative LOE 908 selectively blocks vasopressin-activated nonselective cation currents in A7r5 aortic smooth muscle cells

Abstract

The effect of (R,S)-(3,4-dihydro 6,7-dimethoxy-isoquinoline-1-yl)-2-phenyl- N,N-di-[2-(2,3,4-trimethoxyphenyl)ethyl]-acetamide (LOE 908), a cation channel blocker in HL-60 promyeloblasts, was studied in the A7r5 smooth muscle cell line from rat thoracic aorta, using the whole-cell patch-clamp technique. At a holding potential of -60 mV, application of vasopressin induced a nonselective cation conductance in voltage-clamped A7r5 cells. The current-voltage relation was linear, and currents reversed close to 0 mV regardless of the chloride gradient. The activation of the nonselective cation conductance by vasopressin was not affected by dialysing cells with Ca(2+)-free internal solution. LOE 908 blocked this current in a concentration-dependent manner with an IC50 of 560 nM, whereas dihydropyridine-sensitive Ba2+ current through voltage-dependent Ca2+ channels was blocked with an IC50 of 28 microM. Another organic blocker of receptor-mediated Ca2+ entry, 1-beta-[3-(4-methoxyphenyl)-propoxy]-4-methoxyphenethyl-1H-imidazole hydrochloride (SK&F 96365), blocked both, the vasopressin-induced nonselective conductance and the voltage-activated Ba2+ current with similar IC50 values of 13 microM and 8 microM, respectively. The rank order of potency of inorganic blockers on the vasopressin-induced inward current was Gd3+ > La3+ > Cd2+. Vasopressin-induced non-selective cation current was also observed in pertussis toxin-pretreated A7r5 cells but was completely abolished after infusion of the GDP analogue, guanosine 5'-O-[3-thio]diphosphate, from the patch pipette. Furthermore, vasopressin induced a transient outward current, suggesting a Ca(2+)-activated K(+)-current, which overlapped with the nonselective cation conductance.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacological and Electrophysiological Characterization of Store-Operated Currents and Capacitative Ca2+Entry in Vascular Smooth Muscle Cells

“…2C). 2) I CAT activated by 100 nM AVP in A7r5 cells was inhibited by LOE 908 (Krautwurst et al, 1994), but LOE 908 did not inhibit I SOC (Brueggemann et al, 2005). 3) AVP-activated I CAT is enhanced by flufenamate (Jung et al, 2002), whereas I SOC is inhibited by flufenamate (Fig.…”

“…In A7r5 cells, AVP was previously found to activate both CCE and NCCE (Byron and Taylor, 1995;Broad et al, 1999). Previous electrophysiological studies identified a nonselective cation current (I CAT ) in A7r5 cells activated by high [AVP] (100 nM; Van Renterghem et al, 1988;Krautwurst et al, 1994;Nakajima et al, 1996;Iwasawa et al, 1997;Jung et al, 2002), which may relate to AVP-activated NCCE. I CAT is clearly distinct from I SOC in several ways.…”

Regulation of TRPM2 channels in neutrophil granulocytes by ADP-ribose: a promising pharmacological target

“…Thus, FFA should be considered at best a starting point for the development of channel blockers that might be useful not only in the lab but in future also in clinical settings. Similar reservations apply to other organic blockers such as LOE908 (Krautwurst et al 1993;Krautwurst et al 1994) or SKF96365 (Merritt et al 1990). …”

Long-Term Maternal Hypoxia

“…Figure 1A and B shows the dose-response curves for 5-HT and the inhibitory influence of 5HT 1B/D and 5HT 2A receptor antagonists. Figure 1C compares the EC 50 values for 5-HT and the actions of the receptor inhibitors. 5-HT 1B/D receptors were inhibited with 1 mmol/L GR-55562 because it has pK B values of 7.3 and 6.3 for human-cloned 5-HT 1B and 5-HT 1D receptors, respectively, and only weak binding to a number of other 5-HT subtypes.…”

“…LOE 908 inhibits native NSCC in A7R5 myocytes that are activated in response to arginine vasopressin but not store depletion. 50,51 Spermine 48,49 in comparison preferentially blocks TRPM4, 5, and 7. The influence of these TRP channel inhibitors on contraction shows that LTH causes subtle changes in the pharmacology that implicate potential changes in the expression of TRPC or TRPM gene products.…”