Alejandro Elizalde

Selective reinnervation of twitch and tonic muscle fibres of the frog.

The electrical properties and innervation of piriformis muscle fibres and the conduction velocities and thresholds of the corresponding motor axons were studied. In normal muscles all fibres clearly fell into the category of twitch or tonic. Tonic muscle fibres were selectively reinnervated by small motor axons after crushing or cutting the piriformis nerve. Twitch fibres were reinnervated by large motor axons. Tonic fibres were also selectively reinnervated by small motor axons when the proximal stump of the piriformis nerve was cut and attached to the caudal end of the muscle. With this procedure the possibility of mechanical guidance by remaining neural sheaths was eliminated. Polyneuronal innervation in twitch fibres in piriformis muscles of normal frogs was 4.7% and in contralateral muscles of operated frogs with the piriformis nerve cut it was 22.6%. Unexpectedly three out of seventeen tonic fibres in contralateral muscles were simultaneously innervated by both small and large motor axons. It is concluded that reinnervation is highly specific for fibre type in frog skeletal muscles.

Cannabinoid receptor type 1 activation by arachidonylcyclopropylamide in rat aortic rings causes vasorelaxation involving calcium-activated potassium channel subunit alpha-1 and calcium channel, voltage-dependent, L type, alpha 1C subunit

Cannabinoids are key regulators of vascular tone, some of the mechanisms involved include the activation of cannabinoid receptor types 1 and 2 (CB); the transient receptor potential cation channel, subfamily V, member 1 (TRPV1); and non-(CB(1))/non-CB2 receptors. Here, we used the potent, selective CB(1) agonist arachidonylcyclopropylamide (ACPA) to elucidate the mechanism underlying vascular tone regulation. Immunohistochemistry and confocal microscopy revealed that CB(1) was expressed in smooth muscle and endothelial cells in rat aorta. We performed isometric tension recordings in aortic rings that had been pre-contracted with phenylephrine. In these conditions, ACPA caused vasorelaxation in an endothelium-independent manner. To confirm that the effect of ACPA was mediated by CB(1) receptor, we repeated the experiment after blocking these receptors with a selective antagonist, AM281. In these conditions, ACPA did not cause vasorelaxation. We explored the role of K(+) channels in the effect of ACPA by applying high-K(+) solution to induce contraction in aortic rings. In these conditions, the ACPA-induced vasorelaxation was about half that observed with phenylephrine-induced contraction. Thus, K(+) channels were involved in the ACPA effect. Furthermore, the vasorelaxation effect was similarly reduced when we specifically blocked calcium-activated potassium channel subunit alpha-1 (KCa1.1) (MaxiK; BKCa) prior to adding ACPA. Finally, ACPA-induced vasorelaxation was also diminished when we specifically blocked the calcium channel, voltage-dependent, L type, alpha 1C subunit (Ca(v)1.2). These results showed that ACPA activation of CB(1) in smooth muscle caused vasorelaxation of aortic rings through a mechanism involving the activation of K(Ca)1.1 and the inhibition of Ca(v)1.2.

Forskolin versus sodium cromoglycate for prevention of asthma attacks : a single-blinded clinical trial

To determine the efficacy of forskolin in preventing asthma attacks, we performed a single-blinded clinical study in children and adult out-patients at a public hospital in Mexico. Forty patients of either sex with mild persistent or moderate persistent asthma were assigned randomly to 6 months of treatment with forskolin at 10 mg/day orally (capsules) or with two inhalations of sodium cromoglycate every 8 h, i.e. three times a day. The number of patients who had asthma attacks during the treatment period was significantly lower among those receiving forskolin (8/20, 40%) than among those receiving sodium cromoglycate (17/20, 85%). Values of forced expiratory volume in 1 s and forced expiratory flow, mid-phase, were similar in the two groups during the treatment period. We conclude that forskolin is more effective than sodium cromoglycate in preventing asthma attacks in patients with mild persistent or moderate persistent asthma.

Characterization of the effects of histamine on the transmembrane electrical activity of guinea-pig and rabbit SA- and AV-node cells

SummaryThe effects of histamine on the transmembrane electrical activity of cells of small preparations (0.5 × 0.5 mm) of guinea-pig and rabbit sinoatrial- and atrioventricular-nodes were studied. Histamine at concentrations above 10−7 mol/l increased the firing rate, the rate of diastolic depolarization, the maximum diastolic potential, the amplitude and the maximum rate of depolarization of the action potential of pacemaker cells of rabbit and guineapig sinoatrial cells and rabbit atrioventricular cells. These effects were antagonized by the HZ-receptor blocker cimetidine (2.5 × 10−6 mol/1) but they were not modified by the H1-receptor blocker chlorphenamine (2.5 and 5×10−6 mol/1). Small preparations of guinea-pig atrioventricular node did not exhibit spontaneous activity, but it was induced by histamine and blocked by cimetidine. Histamine increased the maximum upstroke velocity of propagated action potential of cells of the central part of complete atrioventricular node in both species studied. These effects were blocked by cimetidine, but not by chlorphenamine. It is concluded that the increase in automaticity induced by histamine in guinea-pig and rabbit sinoatrial and atrioventricular nodes was due to stimulation of H2receptors. Histamine did not depress electrical activity of atrioventricular node cells, but rather increased it. This effect was due to H2-receptor stimulation.

Effects of the novel antiarrhythmic compound TR 2985 (ropitoin) on action potentials of different mammalian cardiac tissues

SummaryRopitoin (TR 2985) is a novel antiarrhythmic drug. In the present work we have found that the main effect of the compound on the normal action potential of different cardiac tissues, guinea-pig atrial and ventricular muscle (1–3 μmol/l), and dog Purkinje fibres (0.5–1.0 μmol/l) was a depression of the maximum upstroke velocity. This effect was dependent on the frequency of stimulation, being stronger at higher frequencies. In the presence of the drug (3 μmol/l), we observed a shift of 9 mV of the resting membrane potential-maximum upstroke velocity relationship to more negative potentials. Under control conditions recovery from inactivation of maximum upstroke velocity was complete in less than 200 ms. Ropitoin induced a very slow component of recovery of the maximum upstroke velocity, explaining the frequency-dependent effects of the drug. The slow recovery of the maximum upstroke velocity induced by ropitoin was dependent on the membrane potential being faster at a more hyperpolarized membrane potential. The time course of the recovery was also dependent on pH; acidosis slowed it considerably. Ropitoin increased action potential duration of atrial muscle at 20% and 90% of repolarization. In contrast, the compound shortened action potential duration of ventricular muscle at 20% and 90% of repolarization, and dog Purkinje fibres at 50% and 90% of repolarization. In addition, ropitoin (1–3 μmol/l) depressed guinea-pig ventricular slow action potentials. This effect was the stronger the higher the stimulation frequency.

ACPA and JWH-133 modulate the vascular tone of superior mesenteric arteries through cannabinoid receptors, BKCa channels, and nitric oxide dependent mechanisms

BACKGROUND Some cannabinoids, a family of compounds derived from Cannabis sativa (marijuana), have previously shown vasodilator effects in several studies, a feature that makes them suitable for the generation of a potential treatment for hypertension. The mechanism underlying this vasodilator effect in arteries is still controversial. In this report, we explored how the synthetic cannabinoids ACPA (CB1-selective agonist) and JWH-133 (CB2-selective agonist) regulate the vascular tone of rat superior mesenteric arteries. METHODS To screen the expression of CB1 (Cannabinoid receptor 1) and CB2 (Cannabinoid receptor 2) receptors in arterial rings or isolated smooth muscle cells obtained from the artery, immunocytochemistry, immunohistochemistry, and confocal microscopy were performed. In addition, the effects on vascular tone induced by the two cannabinoids were tested in isometric tension experiments in rings obtained from superior mesenteric arteries. The participation of voltage and calcium-activated potassium channel of big conductance (BKCa) and the role of nitric oxide (NO) release on the vascular effects induced by ACPA and JWH-133 were tested. RESULTS CB1 and CB2 receptors were highly expressed in the rat superior mesenteric artery, in both smooth muscle and endothelium. The vasodilation effect shown by ACPA was endothelium-dependent through a mechanism involving CB1 receptors, BKCa channel activation, and NO release; meanwhile, the vasodilator effect of JWH-133 was induced by the activation of CB2 receptors located in smooth muscle and by a CB2 receptor-independent mechanism inducing NO release. CONCLUSIONS CB1 and CB2 receptor activation in superior mesenteric artery causes vasorelaxation by mechanisms involving BKCa channels and NO release.