Inhibition by ω‐conotoxin GVIA of the chronotropic responses to sympathetic and parasympathetic nerve stimulation in the isolated, blood‐perfused atrium of the dog

Abstract

1. We investigated the effects of omega-conotoxin GVIA (omega-CgTX), a blocker of N-type voltage-operated calcium channels, on the chronotropic response to stimulation of the intracardiac sympathetic and parasympathetic nerves in the isolated, blood-perfused right atrium of the dog. 2. omega-CgTX (0.3-3 nmol) itself did not affect the sinus rate significantly, but it inhibited the negative followed by positive chronotropic response to simultaneous stimulation of sympathetic and parasympathetic nerves in a dose-dependent manner. 3. omega-CgTX at higher doses (1-3 nmol) inhibited the positive response to sympathetic stimulation more strongly than the negative response to parasympathetic stimulation. omega-CgTX (3 nmol) abolished the positive chronotropic response to sympathetic nerve stimulation in the atrium treated with atropine, but did not abolish the negative response to selective parasympathetic stimulation. Neither the chronotropic response to noradrenaline nor the response to acetylcholine was affected by omega-CgTX. 4. These results indicate that omega-CgTX inhibits not only the response to sympathetic stimulation but also the response to parasympathetic stimulation in the dog heart and it inhibits the positive chronotropic response to sympathetic stimulation more strongly than the negative chronotropic response to parasympathetic stimulation.

Effects of Neuropeptide Y on Intrarenal Hemodynamics, Plasma Renin Activity and Urinary Sodium Excretion in Rats

“…NPY might have either no or a positive chronotropic effect [27,28]. Similar observations have been made in innervated heart preparations [29][30][31]. The situation is particularly complex in intact animals.…”

Heterogeneity of prejunctional NPY receptor‐mediated inhibition of cardiac neurotransmission

“…The lack of postjunctional modulation or potentiation of the e ects of exogenous agonists acting at the sinoatrial node has been reported by others in dog (Potter, 1987;Ren et al, 1991), rat (Pardini et al, 1992) and guinea-pig Pardini et al, 1992). These experiments suggest that the site of action of NPY at the parasympathetic neuroe ector junction is most likely to be prejunctional.…”

Characteristics of the Responses of Isolated and Perfused Canine Splenic Arteries to Vasoactive Substances and to Periarterially Electrical Stimulation

“…Even though the cannula insertion method has been used for about ten years, perivascular nerve stimulation has not been well established (6)(7)(8). According to our experience with direct electrical stimula tion to the tissues that contain sympathetic nerve fibers (32,33), a stimulation with a pulse duration of more than 2 msec and a voltage of more than 20 V will burn the tis sues that come in contact with the electrodes, and a stimu lation with much higher frequency and potent current will evoke muscle contraction. The use of an excessive amount of electrical stimulation in the past may be due to the lower levels of innervation of the arteries used and pos sibly the experimental technique (6 8).…”