Xaviera García

Vasoconstrictor effect of Cissus sicyoides on guinea-pig aortic rings

1. The effect of the aqueous extract of Cissus sicyoides (CS) on isolated guinea pig aortic rings was studied. CS contracts the smooth muscle of the aorta in a dose-response relation. 2. The extract of CS increases the norepinephrine contraction in normal calcium and in solutions without calcium. 3. Lanthanum inhibits the contraction induced by CS. 4. The vasoconstrictor effect of CS was increased in solutions without calcium or with low calcium, which is an inverse calcium-dependent contraction. 5. Prolonged exposure to calcium-free solution did not abolish CS contraction. These contractions can be elicited repeatedly even after 6 hr of continuous exposure to calcium-free solutions. 6. Caffeine reduces contractile response induced by CS in normal calcium, as well as in solutions without calcium. 7. Our results support the idea that the aqueous extract of CS acts at the membrane level, increasing the calcium entry through the membrane as well as acting on the internal calcium deposits, possibly on the sarcoplasmic reticulum.

Actions of perezone on rat smooth muscle.

1. Perezone (PZN) on the in vitro intestinal smooth muscle of the rat relaxes the basal tonus of the smooth muscle, interrupts spontaneous activity and also blocks the contractile response induced by ACh, K+, and Ba2+; these actions are dose dependent. 2. Although in presence of small doses of PZN, the isometric contractile response to ACh was increased. 3. In calcium free intestinal smooth muscle preparation, the addition of PZN in low dose before Ca2+ increased the contractile effect of added calcium to the bath, but in presence of high doses of PZN the response to calcium was depressed. 4. PZN in calcium free preparations antagonized the contraction caused by adding barium. 5. These findings suggested that with small doses of PZN more availability of intracellular calcium free exist and/or an increase in excitability and/or an inhibition of AChase could coexist. 6. The responses of the intestine to high doses of PZN were possibly in part by blocking calcium entry. 7. The smooth muscle responses to PZN suggest that it has a membranal effect and/or an action on the internal calcium stores possibly increasing the intracellular calcium concentration. It is likely to be the expression of an increase in the intracellular calcium concentration above the levels normally reached that would be responsible for uncoupling of the smooth muscle, which would occur if the [Ca2+]i rises excessively.

An electrically operated micro-tap

Summary A device is described which allows controlled application of non-ionized drugs and proteins to discrete areas of the surface of muscle cells. It consists of two concentric micro-pipettes arranged so that the tip of the inner one, which is attached to a coil moving in a magnetic field, plugs from the inside the tip of the outer pipette which contains the drug solution. The aperture of the tap can be controlled accurately by energizing the coil with current pulses as short as 50 msec. Experiments are briefly described in which the operation of the micro-tap was tested by applying acetylcholine to the end-plates of frog muscle.

Effect of stress on the Schultz-Dale reaction in guinea pig aorta.

The smooth muscle of thoracic aorta from guinea pig sensitized with egg albumin (EA) produced an anaphylactic contraction when it was exposed to EA. Experiments were performed to evaluate stress effects on the anaphylactic contraction in guinea pig aortic rings. Two types of stressors were used as immunosuppressor stimuli: physical restraint and shaking of the animals. Both stressors diminished the amplitude of the Schultz-Dale contraction in aortic rings from sensitized guinea pig. The shake stress stimulus interrupted several times during each session induced higher immunosuppression in animals in which the active sensitization and the stress sessions began the same day. Severe restraint stress, prior to active immunization, also suppressed significantly the anaphylactic response. The Schulz-Dale reaction in guinea pig aorta seems to be a valuable technique to study the stress effects on the anaphylactic response.

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.

Effect of the length of degenerating phrenic nerve fibres on the anaphylactic contraction of the diaphragm.

1. The effect of denervation on the anaphylactic contraction of the diaphragm from actively sensitized guinea pig has been studied. 2. The section of the phrenic nerve took place at cervical and thoracic levels. The sensitization of the animal took place several days before sectioning, simultaneously with denervation and after denervation. 3. The anaphylactic contractions were observed from the fourth day after thoracic denervation, and from the sixth day when denervation was in the cervical region. 4. The hypersensitivity to ACh in the denervated diaphragmatic muscle was present 24 hr after sectioning the phrenic nerve and reached its maximum 3-4 days after. 5. These results support the idea that denervation caused some changes in the membrane of the skeletal muscle fibres to allow the fixation of antibodies. These denervation changes are dependent on the length of the peripheral nerve left to degenerate. Anaphylactic contractions appeared earlier in those animals where phrenic nerve sections were closer to the diaphragmatic muscle.

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.

Anaphylactic contraction of guinea pig smooth muscle passively sensitized with chicken antiserum

1. Actively sensitized guinea pig intestine responds, typically, with a large contraction to the first application of antigen (Ag). This is followed by a spontaneous relaxation of the tissue, while still in the presence of the Ag and a rapid desensitization, i.e. further exposures to Ag fail to evoke new contractions. 2. In contrast when the guinea pig was passively immunized with chicken antiserum, the first dose of Ag produced a sustained contraction. The second and third doses elicited contractions of comparable magnitude and no desensitization occurred. 3. In addition, consecutive Schultz-Dale reactions of guinea pig intestine or uterus from animals passively sensitized with chicken antiserum showed a consistent potentiation. They reached a maximal amplitude when the tissue was exposed to the Ag 6-7 times. Such a potentiation is abolished by storing the preparations up to 48 hr at 4 degrees C. 4. The tissues from chickens passively immunized with homologous antisera showed the same behaviour as those taken from actively sensitized chicken, i.e. no desensitization was observed. 5. These results agree with those previously observed in our laboratory suggesting the existence of a special property of the chicken antibodies (Ab). Indeed, the characteristic features of the anaphylactic reaction in actively sensitized chickens were transmitted to both chickens and guinea pigs passively sensitized with chicken Abs.