Pharmacology of pH effects on carotid body chemoreceptors in vitro

Abstract

SUMMARY1. The carotid body and the carotid nerve were removed from anaesthetized cats and placed in a small Perspex channel through which Locke solution (at various pH values and usually equilibrated with 50 % 02 in N2) was allowed to flow. The glomus was immersed in the flowing solution while the nerve was lifted into oil covering the saline. Sensory discharges were recorded from the nerve and their frequency was used as an index of receptor activity. At times, a small segment of carotid artery, containing pressoreceptor endings, was removed together with the glomus. In this case, pressoreceptor discharges were recorded from the nerve.2. The amplitude of either chemo-or pressoreceptor discharges was not changed by strong acid solutions. Acid decreased the frequency of the baroreceptor discharges only when pH fell to less than 4-0. Solutions at low pH increased the chemosensory discharge, but acid depressed the increased chemoreceptor discharge elicited by KCI. These experiments indicated that H+ ions probably acted as membrane 'stabilizers' without depolarizing either the nerve fibres or endings.3. Acid solutions increased the action of acetylcholine chloride (AChCl)

Effects of Dihydro‐β‐Erythroidine on the Cat Carotid Chemoreceptors

“…In the present experiments DHE had no immediate or long-term effect on spontaneous chemoreceptor discharge, in contrast to the marked stimulation found in vitro by Eyzaguirre and Zapata [1968b], and nor was the reduction in response to ACh as long-lasting as they found. These disparities could result from fundamental differences in the preparations.…”

“…very rapidly and effectively [see Curtis and Eceles, 1958] and is a good antagonist of the nicotinic action of acetylcholine (ACh) on Renshaw cells [Eccles, Fatt and Koketsu, 1954;Eccles, Eceles and Fatt, 1956;Curtis and Ryall, 1966]. It seemed worth using quantitative neuropharmacological techniques to investigate whether DHE could prevent the effects of physiological and pharmacological stimuli on the cat carotid chemoreceptors in vivo, as it is apparently capable of doing in vitro [Eyzaguirre and Zapata, 1968b].…”

The release of acetylcholine from carotid body tissues. Further study on the effects of acetylcholine and cholinergic blocking agents on the chemosensory discharge

“…EYZAGUIRRE AND P. ZAPATA Evidence has been presented elsewhere which indicates that the sensory terminations are probably activated indirectly by different stimulating agents such as low Po2, high PcO2, acidity or electrical currents (Eyzaguirre & Koyano, 1965a, b, c; Ezyaguirre & Zapata, , 1968. In fact, activation of the nerve terminals seems to be accomplished by a chemical released from the glomus tissue (Eyzaguirre, Koyano & Taylor, 1965).…”

“…METHODS The general methods employed in this study have been described elsewhere (Eyzaguirre & Koyano, 1965a;Eyzaguirre et al 1965;Eyzaguirre & Zapata, 1968). Details of the various experiments are given in the Results.…”

Evidence for two types of nicotinic receptors in the cat carotid body chemoreceptor cells

“…thectomy Gomez-Nino, unpublished .Õ ur findings with mecamylamine vs. a-BT clearly demonstrate that part of the nicotinic receptors in the cat CB are not sensitive to the snake toxin. Although the present pharmacological study does not allow to identify the subtypes of nicotinic receptors, it is clear that chemoreceptor cells should express nicotinic receptors with a or 7 a subunits, because only these subunits bind a-BT; it is 8 also clear that they must express nicotinic receptors with other a subunits, probably of the subtypes a or a 3 5 which are the most commonly found in sympathetic neuw x rons, and PC12 cells 19 which are embryologically related to the CB. Our findings in turn indicate that previous identification of nicotinic receptors on the basis of a-BT binding and autoradiographic studies have let out part of the nicotinic receptors in the CB, and the possibility exists that a part of these missed receptors are located in the sensory nerve endings.…”