Paramecium calcium channels are blocked by a family of calmodulin antagonists.

Abstract

Although the voltage-sensitive Ca channel present in Paramecium has been subjected to detailed physiological and genetic analysis, no organic ligands have been described that block this channel with high affinity and that ultimately can be used to identify channel components. Based on a previous observation that the naphthalene sulfonamide calmodulin antagonist W-7 can block Paramecium Ca channels at high concentration, we have synthesized analogs of W-7 that block these channels at concentrations of <1 aiM. The effectiveness of these compounds was tested both by a sensitive behavioral assay and on Ca channels that had been incorporated into planar lipid bilayers. Despite the fact that these compounds are effective Paramecium calmodulin antagonists, two independent lines of evidence suggest that W-7 and its analogs block the Ca channel by a mechanism that is independent of their action on calmodulin. In addition, the sensitivity to W-7 or dihydropyridines of Ca channels present in a number of eukaryotic phyla has been used to identify similarities in Ca channels from widely diverse organisms. It appears that the pharmacological specificity provides a means to group Ca channels.

Calcium in ciliated protozoa: Sources, regulation, and calcium-regulated cell functions

“…Alternatively, anti-CaM drugs can affect behavior on the basis of the effects on a variety of currents, which are activated more or less by a Ca 2 +/CaM complex. For instance, W7, i.e., N-(6-aminohexyl)-5-chloro-lnaphthalenesulfonamide, chlorpromazine, R24571 (calmidazolium), or TFP can block voltage-dependent Ca 2 + channels in cilia and, hence, block backward swimming (Haga et aI., 1982;Ehrlich et al, 1988). Inhibitory effects have been recognized with somatic Na+ currents and Kt currents, as we could confirm (Erxleben and Plattner, 1994).…”

Blockade by calmodulin inhibitors of Ca2+ channels in smooth muscle from rat vas deferens

“…These compounds blocked the Ba2+ current flowing through Ca2+ channels ( Figures 3, 4 and 5) at concentrations similar to those required for the inhibition of ionic currents through Ca2+ channels in other cells (Klockner & Isenberg, 1987;Ehrlich et al, 1988). Moreover, the calmodulin inhibitors inhibited [3H]-nimodipine binding (Figure 2).…”

“…However, it has been suggested that these compounds exert effects that are not related to calmodulin inhibition when applied extracellularly (e.g., Klockner & Isenberg, 1987;Hori et al, 1989). Inhibition of Ca2`channels by these compounds was also investigated by electrophysiological techniques in cardiac cells (Klockner & Isenberg, 1987) and in Paramecium (Ehrlich et al, 1988). Klockner & Isenberg (1987) reported that several calmodulin inhibitors reduced Ca2" currents in smooth muscle cells from bovine portal vein.…”

Inhibition of olfactory cyclic nucleotide‐activated current by calmodulin antagonists

“…W-7 has been reported to block various Ca2+ channels and currents (Greenberg et al, 1987;Ehrlich et al, 1988;Nakazawa et al, 1993), voltage-dependent Na' current (Ichikawa et al, 1991), and Ca2"-activated K+ channels (Kihira et al, 1990). Trifluoperazine inhibits Ca2" currents (Greenberg et al, 1987;Nakazawa et al, 1993), voltagedependent Na' current (Ichikawa et al, 1991), Ca2+-activated (McCann & Welsh, 1987;Kihira et al, 1990;Ikemoto et al, 1992) and ATP-sensitive (Muller et al, 1991) K+ channels, and GABA-activated Cl-current (Yang & Zorumski, 1989).…”

“…In ventricular and vascular myocytes, trifluoperazine depressed 'Ca, INa, and IK (Kldckner & Isenberg, 1987). Many of these studies (Greenberg et al, 1987;Klockner & Isenberg, 1987;McCann & Welsh, 1987;Ehrlich et al, 1988;Kihira et al, 1990;Nakazawa et al, 1993) included evidence suggesting that inhibition of channel activity was not mediated by calmodulin.…”