Effect of acetylcholine on the norepinephrine-induced positive chronotropy and increase in cyclic nucleotides of isolated rabbit sinoatrial node.

Abstract

SUMMARY Transmural stimulation of, or application of nicotine to, the isolated rabbit sinoatrial (SA) node resulted in initial negative and late positive chronotropy. Simultaneous application of acetylcholine and norepinephrine produced a similar biphasic chronotropic effect. These procedures produced an initial increase in cyclic guanosine 3':5'-monophosphate (cyclic GMP) and a delayed elevation in cyclic adenosine 3':5'-monophosphate (cyclic AMP). The initial and late effects on rate and nucleotide levels were inhibited by pretreatment with atropine and propranolol, respectively. Pretreatment with atropine shortened the time of maximum increase in cyclic AMP level and heart rate from 3 to 1 minute after the simultaneous application of acetylcholine and norepinephrine and enhanced the positive chronotropic effect. Physostigmine prolonged the duration of the increase in cyclic GMP and negative chronotropic effect after the simultaneous application. These results suggest that when acetylcholine and norepinephrine are present simultaneously in the SA node region, the former interacts predominantly with muscarinic receptors and stimulates the cyclic GMP system, which in effect delays the cyclic AMP elevation and reduces the positive chronotropic effect of norepinephrine. However, these effects of acetylcholine cannot be explained solely on the basis of changes in the cyclic GMP level, because sodium nitroprusside produced a marked elevation of the cyclic GMP levels without decreasing the heart rate and did not affect the norepinephrine-induced increase in pacemaker rate and cyclic AMP. Sodium nitroprusside may affect cyclic GMP pools other than those susceptible to acetylcholine. These cyclic GMP pools may not exert chronotropic effects. Ore Res 45: 493-504, 1979 THE sinoatrial (SA) node of the mammalian heart receives its nerve supply from both the parasympathetic (James and Spence, 1966) and sympathetic (Shindler et al., 1968;Taniguchi et al., 1977) divisions of the autonomic nervous system and, although these two nerves reciprocally regulate the heart rate, the parasympathetic nerve predominates (Voile and Koelle, 1975). Carrier and Bishop (1972) found that when both acetylcholine and norepinephrine were present, the former had a greater effect on heart rate.Previously Taniguchi et al., 1977) that cyclic adenosine 3':5'-monophosphate (cyclic AMP) in the SA node was involved in the positive chronotropic effect of norepinephrine. However, George and associates (1970) snowed that perfusion of the rat heart with acetylcholine resulted in an elevation of cyclic guanosine 3':5'-monophosphate (cyclic GMP) level which paralleled the negative inotropic and chronotropic effects. Watanabe and Besch (1975) suggested that, in the isolated guinea pig ventricle, cyclic GMP mediates the antiadrenergic effects of acetylcholine by specifically antagonizing the inotropic actions of cyclic AMP.Recently, Diamond et al. (1977) showed that sodium nitroprusside markedly increased cat atrial cyclic GMP levels but did not decrease ...

Are acetylcholine‐induced increases in 42K efflux mediated by intracellular cyclic GMP in turtle cardiac pace‐maker tissue?

“…Other possible actions of cyclic GMP which have been suggested include: (i) a specific antagonism of adrenergic, cyclic-AMP-mediated phenomena (Watanabe & Besch, 1975;George, Ignarro, Paddock, White & Kadowitz, 1975;Bailey, Watanabe, Besch & Lathrop, 1979;Taniguchi et al 1979;Bigeon & Pappano, 1980; but see Keely & Lincoln, 1978);…”

“…In addition, their data show that application of sodium nitroprusside (10-3 M) produces a 300 % increase in cyclic GMP concentration but no change in action potential duration, and that cyclic GMP analogues cause no significant electrophysiological changes. Taniguchi, Fujiwara, Lee & Hidaka (1979) found that either transmural stimulation or application of acetylcholine (10-8-10-6 M) in rabbit sino-atrial node causes a marked, atropinesensitive elevation ofcyclic GMP. However, increased levels ofcyclic GMP (500-600 %) produced by application of sodium nitroprusside (10-4 M) did not result in a decrease in heart rate.…”