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Am J Physiol Regul Integr Comp Physiol 274: R677-R685, 1998;
0363-6119/98 $5.00
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Vol. 274, Issue 3, R677-R685, March 1998

K+ channel blockade in the NTS alters efficacy of two cardiorespiratory reflexes in vivo

James W. Butcher and Julian F. R. Paton

Department of Physiology, School of Medical Sciences, University of Bristol, Bristol BS8 1TD, United Kingdom

We investigated the role of potassium conductances in the nucleus of the solitary tract (NTS) in determining the efficacy of the baroreceptor and cardiopulmonary reflexes in anesthetized rats. The baroreceptor reflex was elicited with an intravenous injection of phenylephrine to evoke a reflex bradycardia, and the cardiopulmonary reflex was evoked with a right atrial injection of phenylbiguanide. Microinjection of two Ca-dependent potassium channel antagonists (apamin and charybdotoxin) into the NTS potentiated the baroreceptor reflex bradycardia. This may reflect the increased neuronal excitability observed previously in vitro with these blockers. In contrast, the Ca-dependent potassium channel antagonists attenuated the cardiopulmonary reflex, whereas voltage-dependent potassium channel antagonists (4-aminopyridine and dendrotoxin) attenuated both the baro- and cardiopulmonary reflexes when microinjected into the NTS. The possibility that the reflex attenuation observed indicates a predominant distribution of certain potassium channels on gamma -aminobutyric acid interneurons is discussed.

baroreceptor reflex; cardiopulmonary reflex; 4-aminopyridine; dendrotoxin; apamin; nucleus of the solitary tract


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