Neomycin: A novel potent blocker of communication between T‐tubule and sarcoplasmic reticulum

Abstract

Ca 2÷ release from the sarcoplasmic reticulum (SR) was induced in isolated triads by direct stimulation of the SR moiety by polylysine, or stimulation via chemical depolarization of the transverse tubule (T-tubule) moiety. Polylysine-induced release was blocked by neomycin with an IC50 (the concentration for half-maximal inhibition) of 0.3 pM. However, the IC50 for neomycin block of depolarization-induced Ca 2÷ release sharply decreased in a voltage-dependent fashion, and it was 5.3 nM at a maximal extent of T-tubule depolarization. These results suggest that the high affinity binding of neomycin to the triad leads to the specific blocking of the signal transmission from T-tubule to SR.

Polyamine Triggering of Exocytosis in Paramecium Involves an Extracellular Ca 2+ /(Polyvalent Cation)-Sensing Receptor, Subplasmalemmal Ca-Store Mobilization and Store-Operated Ca 2+ -Influx via Unspecific Cation Channels

“…This may occur from the inside, though unrelated to IP 3 . One possibility is inhibition by neomycin of communication be- tween cell membrane and cortical stores, as found in muscle cells [99]. Would our conclusions be compatible with previous extensive experiments by other groups applying neomycin to ciliates?…”

“…As stated, neomycin can permeate into cells when applied for min [55,65]. It then can block some intracellular functions, like communication between cell membrane and SR in striated muscle [99] or in smooth muscle cells [65], as it could in our unpublished results with Paramecium. Particularly the multiple effects of neomycin, e.g., in pyramidal neurons [50], restrain us from any further interpretation of any effects seen in ciliates.…”

Proton pumping by NADH:ubiquinone oxidoreductase. A redox driven conformational change mechanism?

“…N1a is bound to the 24 kDa subunit [27,28]. In bovine complex I, this cluster has the lowest redox midpoint potential (E m;7 = 3370 mV) and exhibits a pH dependence of 360 mV/ pH [29,30].…”

Ferredoxins of the third kind

“…A signi¢cant example is NADH-ubiquinone oxidoreductase (complex I) of mitochondrial and bacterial respiratory chains [8]. The NuoE (or NQO2, or 24 kDa) subunit of this complex displays sequence similarities, particularly with respect to the cysteine distribution pattern [38], and shares spectroscopic idiosyncrasies with thioredoxin-like [2Fe^2S] Fds [43]. The main di¡erences are the larger size of NuoE (180^240 residues), mostly due to the presence of a ca.…”

“…The CbiW protein (total length 127 residues, GenBank CAA04306) from B. megaterium is encoded by a gene belonging to the cobalamin biosynthesis operon (cob) [37]. The NuoE subunit (total length 239 residues) of complex I is from Paracoccus denitri¢cans ( [38], Gen-Bank A40296). The HydC (or HndA [9]) subunit (total length 161 residues) of hydrogenase is from Thermotoga maritima ( [39], GenBank AAC02684).…”