[Effect of caffeine and glycerin on the Ca transport system of sarcoplasmic reticulum fragments from frog skeletal muscles]. / Vliianie kofeina i glitserina na Ca-transportnuiu sistemu fragmentov sarkoplazmaticheskogo retikuluma skeletnykh myshts liagushki.

Parameters of the Ca2+-ion transport system by a fragmented sarcoplasmic reticulum isolated from phasic and tonic frog skeletal muscles were investigated under the action of caffeine or caffeine in combination with glycerol. No changes were observed in the Ca-transport system of a light fraction of the sarcoplasmic reticulum under the influence of caffeine and caffeine-glycerol combination. Caffeine reduced the value of Ca/ATP and enhanced the outflux of Ca2+-ions from membrane fragments of the caffeine-sensitive sarcoplasmic reticulum fraction of both the muscles; the combined effect of caffeine and glycerol was analogous to the action of caffeine applied alone. It is concluded that the potentiation of muscle contraction in the presence of glycerol is not due to the excess of Ca-release from the sarcoplasmic reticulum caused by this agent.

[Passive binding of Ca2+ by fragments of the sarcoplasmic reticulum of frog skeletal muscles]. / Passivnoe sviazyvanie Ca2+ fragmentami sarkoplazmaticheskogo retikuluma skeletnykh myshts liagushki.

A calcium binding characteristics of outside and inside vesicles as well as effects of K+, Mg2+, and acetylcholine cation on the calcium binding were studied in fragments of sarcoplasmic reticulum (SRF), isolated from frog femoral and abdominal muscles; high permeability of the preparations for Ca2+ was produced by incubation with I mM EDTA (pH 8-8.5) or with 5-10 microM ionophor X587A. Three types of Ca2+ binding were observed in the both SRF preparations: two of them exhibited the specific binding with high (K1) and low (K2) affinity and one type of unspecific binding with low affinity (Kunsp). The number of sites (n- nmol of Ca2+/mg of SRF protein) and dissociation constants (K microM) were the following SRF from abdominal muscle--n1 120, (K(1)15); n2 190, (K(2)135); Nunsp 650, (Kunsp 1625); SRF from femoral muscle--n(1)80, (K(1)64); n(2)265, (K(2)189); nunsp 500, (Kunsp 2240). The specific binding of Ca2+ in the SRF preparations was unaltered under physiological conditions in presence of KC1 0.1 M and MgCl2 1 mM if acetylcholine was added at concentration 10 mM, but the Ca2+ binding was completely inhibited at concentration 20 mM of acetylcholine. The unspecific Ca2+ binding was already inhibited at low concentrations of acetylcholine.

[Some properties of transport ATPases in functionally different muscles]. / Nekotorye svoistva transportnykh ATPaz funktsional'no razlichnykh myshts

The properties of Ca-transporting system in sarcoplasmic reticulum membranes in fast and slow frog muscles as well as some properties of sarcolemma Na, K-ATPase of the same object were investigated. The rate of Ca2+ uptake, Ca-ATPase activity and Ca/ATP ratio for the reticulum of fast muscle demonstrated higher values than those for the reticulum of slow muscle. The rate of Ca2+ accumulation by the fragments of the rectus reticulum and Ca/ATP ratio were found to decrease under the influence of acetylcholine (0.05-5 mM). The transport system of the sartorius reticulum was found to be less sensitive to acetylcholine. The peak activity of Na, K-ATPase in femoral muscles of the frog occurred at 80 mM NaCl and 60 mM KCl, whereas in the rectus abdominal muscle it equalled 100 mM NaCl and 40 mM KCl. Thus, Na, K-ATPase activity in the slow muscle was predominantly higher than that in the mixed (femoral) muscles. If the sarcolemma preparations of the muscles of both types the inhibitory effect of acetylcholine on Na; K-ATPase was registered. The enzyme of slow muscles exhibited higher sensibility to acetylcholine.