José del Castillo

Fine structure and innervation of an annelid muscle with the longest recorded sarcomere

Abstract The fine structure of myoepithelial cells of the proventriculus of a marine annelid ( Syllis spongiphila ) is described. The contractile system of these muscle fibers includes a single medial Z band. The thick filaments possess a ~140 A paramyosin-like periodicity, but the filament disposition in these cells corresponds to that of other striated muscles, and actin orbitals in the A band number up to 20. The distance between the centers of the two H bands in the largest cells is ca . 40 µ Dyads involving T-system invaginations and isolated vesicles of the sarcoplasmic reticulum are situated at all sarcomere levels. Insertions of the contractile material onto invaginations of the inner and outer cell surfaces are described. Presumed polyaxonal neuromuscular junctions are established across wide synaptic clefts and include terminals with spherical and non-spherical synaptic vesicles. Inclusions occupying the core of each muscle cell appear to be rich in magnesium.

Depolarization and potentiation of responses to acetycholine elicited by ATP on frog muscle

Abstract Buchtal and collaborators reported thirty years ago an excitatory action of low (10 −3 M) concentrations of ATP on frog muscle, as well as in increase in the sensitivity of the muscle to ACh. These effects have been re-investigated employing both intra-and extra-cellular recording and the technique of iontophoretic drug application. ATP at a concentration of 10 −4 M decreases the recorded resting potential by about 35%. The depolarizing action of ATP is more pronounced in the tibial end of the frog sartorius muscle than in the nerve free pelvic end. In addition ATP, added to the bath and electro-osmotically applied, increases the depolarizing action of ACh. This potentiating effect is particularly marked in denervated muscles.

Release of packets of acetylcholine and synaptic vesicles elicited by brown widow spider venom in frog motor nerve endings poisoned by botulinum toxin

Abstract Homogenates of venom glands of brown widow spiders caused the release of packets of acetylcholine, observed as miniature end-plate potentials (mepps), from nerve terminals in sartorius and cutaneous pectoris muscles of the frog, even though the appearance of mepps which is normally induced by depolarization of the presynaptic membrane had been completely blocked by prior treatment with type A botulinum toxin (BotTX). The distribution of the amplitudes of the recorded mepps resembled that of the mepps in normal muscle and was quite different from the heavily skewed (to the left) distribution of the mepps recorded from BotTX-treated muscles. This suggests that the mepps elicited by brown venom glands homogenates in muscles blocked by BotTX were due to the release of a population of vesicles which is unaffected by BotTX and which is also released on hyperpolarization of nerve terminals.

Generation of calcium action potentials in crustacean muscle fibers following exposure to sulfhydryl reagents

The ventroabdominal flexor muscles of the crustacean Atya lanipes, which are normally completely inexcitable, generate trains of overshooting calcium action potentials after exposure to the sulfhydryl reagents known as alpha, beta-unsaturated carbonyl compounds. The chemically induced action potentials are abolished by protein reagents specific for guanidino and amino groups. Attempts to induce excitability by the use of agents that block potassium conductance were without success. It is proposed that calcium channels are made functional by the covalent modification of a calcium protochannel, via the interaction between the introduced carbonyl group and existing arginine residues.

Succinyl derivatives of N‐tris (hydroxymethyl) methyl‐2‐aminoethane sulphonic acid: their effects on the frog neuromuscular junction

1 Succinic anhydride (SA) dissolved in Ringer solution buffered with N‐tris (hydroxymethyl) methyl‐2‐aminoethane sulphonic acid (SA‐TES solution) potentiates the depolarizing action of acetylcholine (ACh, 10–40 μm) on frog muscle and the tension induced by bath application of this agonist. 2 Applied from one side of a double‐barrelled micropipette, SA‐TES increases the amplitude of iontophoretically elicited ACh potentials. 3 The potentiation of the effects of ACh by SA‐TES does not involve changes in either the activity of the ACh esterase or the input resistance of the muscle membrane. 4 For depolarizations of frog sartorius muscle, dose‐response relationships obtained for ACh concentrations from 0.5 to 20 μm indicate that SA‐TES increases the apparent affinity of ACh by a factor of 3. 5 SA‐TES exerts an ‘accelerating’ effect on the responses elicited by bath‐applied ACh; i.e., it increases the rate of depolarization when ACh is added to the bath and the rate of repolarization upon washing out. These effects are particularly marked in preparations treated with neostigmine (3 μm). 6 SA‐TES does not potentiate the depolarizing action of agonists which do not contain an ester group. Moreover, the time course of the responses elicited by these compounds is not influenced by SA‐TES. 7 SA‐TES fails to influence significantly the effects of the neurally released transmitter. Only a 10% increase in the average amplitude of the endplate potentials was observed. 8 SA hydrolyzes in about 30 min at room temperature; however the SA‐TES solution retains its activity for several weeks. Succinate is inactive, and so is SA in Ringer buffered with phosphate. 9 The SA‐TES solution contains seven succinyl‐TES derivatives, which were separated by ion‐exchange chromatography and paper chromatography. At concentrations between 1 to 150 μm, these succinyl‐TES derivatives affected the ACh‐induced contraction of frog rectus abdominus muscle. The most abundant derivative potentiated the action of high doses of ACh, but was inhibitory at lower ones. The other derivatives were mostly inhibitory. 10 These results are discussed in terms of two hypotheses. One postulates the presence of a diffusion barrier formed by groups that bind ACh and are saturated by SA‐TES. The other assumes that SA‐TES acts directly on the ACh receptor exerting its potentiating effect through a cooperative mechanism.

Spontaneous junctional potentials associated with cholinergic transmission in Peripatus muscle

1. Miniature junctional potentials (m.j.p.s.) were recorded from muscle fibers of isolated dorsal longitudinal muscles of Peripatus at almost any location of randomly-inserted intracellular microelectrodes. Before penetration “external” m.j.p.s. were often observed. 2. The m.j.p. population always included a few of large size (3–5 mV) and others with a slow rise-time. 3. Their mean frequency was high, up to 25 per sec. The amplitude histograms were heavily skewed towards the left. 4. The occurrence of m.j.p.s was random, with no coupling between the events giving rise to them. 5. The amplitude of the spontaneous m.j.p.s was enhanced 3–5-fold by neostigmine (3 × 10−6 w/v). 6. Local depolarizations could be elicited by iontophoretically applied acetylcholine, often with a step indicating the presence of two sets of receptors at different distances from the tip of the micropipette. 7. The acetylcholine-induced depolarizations led to spike discharges. 8. The m.j.p.s were not affected by either atropine or tetrodotoxin but they were blocked by high concentrations (10−4 w/v) of D-tubocurarine.

Non-desensitizing in vitro anaphylactic reaction of chicken visceral muscle.

1. The contractions elicited in pieces of small intestine of actively immunized young chickens upon exposure to the specific antigen (Ag), or Schultz-Dale reaction, have been compared to similar responses of sensitized guinea-pig intestine. 2. Guinea-pig intestine responds, typically, with a large contraction to the first application of Ag. This is followed by a spontaneous relaxation of the preparation, while still in the presence of the Ag, and a rapid desensitization; i.e. further exposures to Ag fail to evoke new contractions. 3. In marked contrast, chicken intestine responds to the Ag with a contraction that remains at its maximal initial value for ca 5 min and then declines only slowly. 4. Exposure to the Ag does not desensitize chicken intestine, which relaxes upon washing out the antigenic protein but contracts again when this is re-introduced in the bath. 5. In addition, consecutive Schultz-Dale reactions of chicken intestine showed a consistent potentiation. They reached a maximal amplitude when the tissue was exposed to the Ag 5-7 times. Such a potentiation is abolished by storing the preparations for 24 hr at 4 degrees C. 6. These observations are discussed in terms of the known properties of avian antibodies.

Influence of formamide on the electrical and mechanical properties of the guinea pig ventricle

1. Guinea pig papillary muscle in vitro upon exposure of Formamide (FMD) exerts a dose dependent positive inotropic effect. 2. The increase in tension developed by papillary muscle is associated with a marked decrease in the duration of the action potential. 3. The increase in extracellular calcium concentration does not modify the positive inotropic effect, but increases the duration of the action potential. 4. FMD markedly potentiate the increase in tension induced by caffeine 3 M suggesting a possible synergetic effect upon the release of Ca2+ ions from the S.R. 5. These experiments suggest that FMD increases the intracellular calcium concentration by exerting a direct action on intracellular calcium stores.

Relaxing action of a holothurian toxin on mammalian smooth muscle

Abstract 1. The crude epidermal mucous secretion produced by the sea cucumber Holothuria mexicana Ludwig inhibits the tonus and spontaneous mechanical activity of rabbit ileum at concentrations of 0.1 mg/ml and higher. 2. This effect, similar to that of epinephrine, is attributed to a compound referred to as mucotoxin (MuTX). 3. MuTX also relaxes strips of the rabbit aorta contracted by 10 −8 M norepinephrine and exerts a similar, less marked, effect on the same strips contracted in high potassium solutions. 4. These observations suggest that the relaxing effect of MuTX on mammalian smooth muscle is not mediated by an adrenergic mechanism.