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At least 1,207 records · Page 67Linked to original sources
PubMed1988

Time course of transmitter action at the sympathetic neuroeffector junction in rodent vascular and non-vascular smooth muscle.

1. Transmitter release from sympathetic postganglionic nerve terminals innervating the guinea-pig and mouse vas deferens and the rat tail artery has been studied in vitro by focal extracellular recording with particular emphasis on the time course of transmitter action underlying the intracellular potential changes. 2. In the absence of stimulation, spontaneous excitatory junction currents (SEJCs) were recorded with amplitudes up to 500 microV and durations between 40 and 100 ms. SEJCs were unaffected by the competitive alpha-adrenoceptor antagonist prazosin but blocked by alpha, beta-methylene ATP which desensitizes P2-purinoceptors. 3. During trains of supramaximal stimuli at 0.1-4 Hz stimulus locked excitatory junction currents (EJCs) were evoked intermittently from the population of varicosities located under the suction electrode. 4. SEJCs were similar in amplitude and time course to EJCs evoked by low-frequency stimulation in the same attachment in all three tissues. 5. SEJCs recorded using either a conventional AC amplifier or a patch clamp amplifier had the same time course. 6. These studies show that the time course of the current underlying the excitatory junction potential is brief and essentially the same in three different tissues. The prolonged time course of the excitatory junction potential in different tissues can be accounted for by the passive membrane properties.

Action Potentials↗
PubMed1984

Dietary manipulation of cardiac and aortic smooth muscle reactivity to isoproterenol.

The responsiveness to isoproterenol of isolated atria and aortic strips was examined in two groups of male Fischer 344 rats. Group A (control) was composed of 5-mo-old rats fed ad libitum; group R (experimental) was composed of rats whose food intake had been restricted for 2 mo to 60% of that consumed by group A. Aortic strips obtained from group R and preconstricted with 30 mM K+ relaxed by 18% when challenged by a maximal concentration of isoproterenol (1 microM). This relaxation was significantly less than the 28% relaxation observed with strips from group A. No effect on the inotropic response of the left atria or on the chronotropic response of the right atria to maximal concentrations of isoproterenol was observed. A slight but statistically significant increase in sensitivity to isoproterenol was observed in the inotropic response of the left atria. The 50% effective concentration (EC50) for the isoproterenol-stimulated increase in force development observed with group R was 0.87 +/- 0.16 X 10(-8) M, which was significantly less than the value of 1.56 +/- 0.28 X 10(-8) M obtained with atria from group A. Food restriction exerted no significant effect on the EC50 for the chronotropic response of right atria to isoproterenol. Both the body weight and the heart weight of group A were greater than those of group R. However, the ratio of heart weight to body weight was significantly greater in group R than in group A.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗