Biomedical subjects

R F McMichael

Publications and source records attributed to R F McMichael.

8 recordsLinked to original sources

PubMed1984

The calcium dependency of mucus glycoconjugate secretion by canine tracheal explants.

Canine tracheal explants, incubated overnight with [14C]-glucosamine, elicited an enhanced secretion of ethanol-precipitated 14C-labelled glycoconjugate when challenged with methacholine, 10 microM. Explants were rendered deficient in total calcium content and unresponsive to methacholine, 10 microM, by incubating them in calcium-free medium for 18 to 22 h; however, the secretory response to the cholinergic agonist was restored with the addition of calcium to the medium. A dose-response relationship resulted when explants were challenged with methacholine in nutrient medium containing varied calcium concentrations (0.45 to 7.2 mM); alterations in the calcium concentration in the absence of methacholine had no significant effect on the basal secretion of 14C-labelled glycoconjugate. The calcium-selective ionophore A23187, 10 microM, stimulated [14C]-glycoconjugate secretion and induced the most significant effect in the presence of nutrient medium containing calcium. Verapamil, 10 microM, a calcium-entry blocker failed to inhibit basal or stimulated [14C]-glycoconjugate secretion; however, the intracellular calcium antagonist TMB-8, 10 to 100 microM, inhibited methacholine-induced [14C]-glycoconjugate secretion in a dose-dependent manner. These data suggest that respiratory mucus secretion is a calcium-dependent process and that intracellular calcium is more vital than extracellular calcium in supporting this phenomenon.

Animals↗

PubMed1983

Effects of calcium and verapamil on vesicourethral smooth muscle of rabbits.

Isolated smooth muscle strips from the rabbit bladder body, bladder base, and proximal urethra were contracted with ionic calcium (Ca2+) alone and with the calcium-selective ionophore A23187, acetylcholine, norepinephrine, adenosine triphosphate (ATP), and direct electrical stimulation. The effects of Ca2+ and the calcium entry blocker verapamil on spontaneous muscle activity and on contractions induced by these agonists were examined. Ca2+ -free Tyrode's solution and verapamil, 1 x 10(-7)M and above, relaxed all of the vesicourethral smooth muscle strips. In addition verapamil, 1 x 10(-8) to 1 x 10(-6) M depending on the particular stimulant employed, noncompetitively inhibited smooth muscle contractions elicited by Ca2+, acetylcholine, norepinephrine, ATP, and direct electrical stimulation. It was concluded that transmembrane Ca2+ influx was important not only in the maintenance of tone and spontaneous phasic muscle activity, but also for the activation of contractions induced by all of the stimulants tested. The data also suggest that intracellular Ca2+ fraction(s) participate in the contractile responses to acetylcholine and norepinephrine challenge, but not to contractions evoked by ATP or electricity.

Acetylcholine↗

PubMed1983

A small animal model study of perlite and fir bark dust on guinea pig lungs.

Fir bark (Abies) and perlite (noncrystalline silicate) dusts have been reported to cause pulmonary disease in humans. Guinea pigs were exposed to either fir bark or perlite dust in a special chamber. Severe pathologic changes occurred in the lungs, consisting of lymphoid aggregated and a perivascular inflammatory response. Both dusts caused similar changes although one was vegetable (fir bark) and the other mineral (perlite). Fir bark and perlite dust appeared to be more than just nuisance dusts.

Aluminum Oxide↗

PubMed1981

The effects of adrenergic agonists and antagonists on vesicourethral smooth muscle of rabbits.

The effects of alpha and beta adrenergic agonists and antagonists on isolated smooth muscle preparations from the rabbit bladder body, bladder base and proximal urethra have been studied. The predominance of alpha receptors in the proximal urethra and the bladder base was observed via contraction of these areas by norepinephrine and blockade by phentolamine. Alpha receptor-mediated contractile activity could be unmasked in the bladder body when beta receptors were blocked with propranolol. Isoproterenol, 1 X 10(-10) to 3 X 10(-7) M, had a strong, dose-related relaxant effect on the bladder body, but little effect on the bladder base or proximal urethra. Selective beta-2 agonists such as terbutaline, salbutamol and ritodrine elicited tissue responses similar to those of isoproterenol. The pD2 values for isoproterenol, terbutaline, salbutamol and ritodrine were 8.59, 7.87, 7.34, and 6.52, respectively. Dobutamine, a selective beta-1 agonist, failed to cause significant relaxation of these tissues. The nonselective beta receptor blocker, propranolol, and the selective beta-2 receptor blocker, butoxamine, competitively antagonized the relaxant effects of the four active beta agonists; however, atenolol, a selective beta-1 receptor blocker, was inactive. On the basis of the selective action of these agonists and antagonists, we concluded that beta-2 receptors mediate relaxation of the vesicourethral smooth muscles of the rabbit and the participation of beta-1 receptors in the areas is insignificant.

Animals↗

PubMed1978

Helium effect on isolated nerve activity.

Various gases were administered to isolated frog sciatic nerves in which action potential amplitudes were recorded in sheathed and desheathed preparations. In the sheathed preparation, nitrogen and argon showed significant anesthetic effects while in the desheathed preparation, helium also depressed the action potential amplitude. In the desheathed frog sciatic nerve, helium demonstrates an anesthetic effect similar to 10(-6) M lidocaine suggesting that at long exposure periods helium may demonstrate anesthetic properties.

Action Potentials↗

PubMed1977

Histamine receptors in urethrovesical smooth muscle.

Through the method of pharmacologic antagonism, the contractile effect of histamine was studied simultaneously on isolated smooth muscle preparations obtained from the body and base of the bladder and from the proximal urethra of the guinea pig. Histamine had a contractile effect mediated specifically through H1 receptors, with no H2 activity. This effect was most marked in the body of the bladder, comparatively moderate in the base, and slight in the proximal urethra. It appears that histamine effect is not mediated through either a cholinergic or an adrenergic mechanism. Clinical implications are discussed.

Acetylcholine↗

PubMed1975

Effect of helium on membrane resistance.

Resistance measurements were made of bimolecular lipid membranes (BLM) according to Mueller and Rudin (10). With the addition of excitability inducing material (EIM), a bacterial protein, the electrical resistance of the BLM was reduced to within biological limits. Frog pericardium was used in the same system as a natural membrane comparison. Exposure of these membranes to air, oxygen and nitrogen resulted in no significant change in the resistance of the bilayers or the pericardium. Exposure to helium and helium 79%-oxygen 21% mixutre resulted in a significant increase in the membrane resistance.

Animals↗

PubMed1975

Cardiovascular and antiarrhythmic effects of carnitine.

Thresholds for electrically induced atrial fibrillation were measured in response to IV carnitine. Mean arterial pressure, heart rate, and mean aortic flow rate were also monitored. Carnitine 100 mg/kg resulted in an increase in mean aortic blood flow. The antiarrhythmic effect was much less than with 5 mg/kg quinidine, but after atropinization, 100 mg/kg carnitine was similar in antiarrhythmic effect to quinidine and did not result in the blood pressure depression seen with quinidine.

Animals↗