The inhibitory effect of manganese on transmitter release at the neuromuscular junction of the toad

Characterization of miniature inhibitory post‐synaptic potentials in rat spinal motoneurones.

“…However, when the Ca2+ was substituted by Mn2+ (3-5 mM), instead of Mg2+, the frequency of miniature i.p.s.p.s markedly increased. An increase of the frequency in Mq2+ saline also occurs with miniature e.p.p.s (Balnave & Gage, 1973). The average frequency and amplitude of miniature i.p.s.p.s in Mn2+ saline was 21-4 Hz and 069 mV, respectively (S.D.…”

“…Secondly, the frequencies of both miniature potentials increased in high external Ca2+ concentrations (Boyd & Martin, 1956;Hubbard, 1961;Hubbard et al 19538a; but see Fatt & Katz, 1952). Thirdly, the frequencies ofboth miniature potentials decreased when external Ca2+ was substituted by Mg2+ (Elmqvist & Feldman, 1965;Blioch et al 1968;Miledi & Thies, 1971), but increased when substituted by Mn2+ (Balnave & Gage, 1973). Fourthly, an increase in K+ concentration markedly increased the frequency of both the miniature potentials only when extracellular Ca2+ was present (del Castillo & Katz, 1954).…”

Calcium dependence of evoked transmitter release at very low quantal contents at the frog neuromuscular junction.

“…Analysis of facilitation at higher quantal contents suggests that with this stimulus pattern the average release to the sixth pulse should be at least 2-3 times the average release to the first pulse (Mallart & Martin, 1967;Magleby, 1973 (Dodge & Rahamimoff, 1967;Balnave & Gage, 1973;Crawford, 1974). Our study of lower evoked release rates demonstrates that during low frequency (0.5-2 Hz) stimulation in 2 mM-Mn2+ (or 4 mM-Co2+) this fourthpower relationship extends down to quantal contents as low as about 0-002, where evoked release rates approach the spontaneous, or 'background', rate of quantal release.…”

“…The most straightforward way to achieve the desired reduction in the quantal content of the (Meiri & Rahamimoff, 1972;Balnave & Gage, 1973;Weakly, 1973;Crawford, 1974), and because higher concentrations of Mn2+ and Co2+ tend to block nerve conduction (our observation; see also Baker, Meves & Ridgway, 1973). Use of these divalent cations allowed us to achieve the desired low quantal contents while still keeping [Ca2+] Solutions were prepared during the course of each experiment from stock solutions containing either no divalent cations, 10 m -MnCl, 10 mM-CoCl2 or 20 mM-MgSO4.…”

Inhibitory Effects of Cations on the Ca2+ Response of Water Fibers in the Frog Tongue

“…Namely, at the neuromuscular junction Ca2+ plays an essential role in the process of the transmitter release (KATZ and MILEDI, 1965) and Sr2+ can replace Ca2+ (MILEDI, 1966;DODGE et al, 1969). In addition, monovalent cations (KELLY, 1965, 1968), Mg2+ (DEL CASTILLO and ENGBAEK, 1954 JENKINSON, 1957), Mn2+ (MEIRI andRAHAMIMOFF, 1972;BALNAVE and GAGE, 1973), Co2+ (WEAKLY, 1973) and La3+ (DEBASSIO et al, 1971) inhibited evoked transmitter release. Similarities of the effects of cations suggest that both tissues have a common mechanism in the process of the activation.…”