On THE RELEASE OF CATECHOLAMINES AND DOPAMINE‐β‐HYDROXYLASE EVOKED BY OUABAIN IN THE PERFUSED CAT ADRENAL GLAND

1 Cat splenic slices prelabelled with [3H]-noradrenaline were incubated in oxygenated Krebsbicarbonate solution at 37°C, and the spontaneous total 3H release into different incubation media monitored. In normal Krebs bicarbonate solution, the spontaneous tritium fractional release amounted to 3.7% of the tissue radiactivity content per 5 min collection period. 2 Tetraethylammonium (TEA) increased spontaneous transmitter release in a concentrationdependent manner; the release was maximal at 30 mM and was 3.5 times the basal release. 3 4-Aminopyridine (4-AP) also enhanced the spontaneous release of tritium. The response increased linearly with 4-AP concentration (1-10 mM). With 10 mM 4-AP, the release was as much as 6 times the basal transmitter release. Guanidine was much less potent than either TEA or 4-AP. 4 The secretory response to TEA or 4-AP was little affected by changes in external Ca2", Mg2+, Na+, Cl-, H2PO4 or by tetrodotoxin. 5 However, transmitter release evoked by TEA or 4-AP strongly depended upon the concentration of HCO3-of the incubation solution; in fact, the secretory response varied almost linearly between I and 25 mM HCO3 . 6 The mechanisms underlying these effects are probably related to the well-known ability ofTEA and 4-AP to block K+ conductance that would cause depolarization of the splenic sympathetic nerve terminals. The HCO3-requirements for the secretory response are probably related to the ability of C02/HCO3-solutions to mobilize and release Ca2+ from intracellular organelles.

Section: Discussioncontrasting

confidence: 54%

Ion dependence of the release of noradrenaline by tetraethylammonium and 4‐aminopyridine from cat splenic slices

Ceña¹,

Garcı́a

González-García³

et al. 1985

“…Left and right adrenal glands were isolated and prepared for retrograde perfusion at room temperature, as described by Garcia, Hernandez, Horga & Sanchez-Garcia (1980). The perfusion rate was approx.…”

Section: Perfusion Of Isolated Adrenal Glandmentioning

confidence: 99%

Effect of Muscarine on Release of Catecholamines From the Perfused Adrenal Gland of the Cat

Kirpekar

Prat

Schiavone

1982

The secretory effect of muscarine was studied in the perfused adrenal gland of the cat. During perfusion of the adrenal gland with Krebs‐bicarbonate solution containing muscarine 480 μm, the rate of catecholamine (CA) secretion was 2.02 ± 0.43 μg/2 min in the first 2 min; thereafter, CA output declined only moderately, to reach about 70% of the initial value after 10 min. Secretory responses to brief infusions of muscarine remained reproducible for at least the first 3 infusions. When the adrenal gland was perfused with muscarine (480 μm), infusions of high K+, nicotine, or veratridine produced their usual responses. A 100 fold lower dose of muscarine also failed to modify these responses. During perfusion with high K+, muscarine evoked a secretory response that was only slightly smaller than the response to muscarine alone. It is concluded that muscarine and nicotine activate CA secretion in the cat adrenal gland by independent mechanisms and that the muscarinic response, unlike the nicotinic response, is not readily desensitized.

“…Both adrenal glands were dissected and prepared for retrograde perfusion as described by Garcia et al (1980). Glands were perfused at a rate of 4mlmin-1, at 37°C with Krebs-HEPES solution pH 7.4, continuously bubbled with pure 02 and having the following composition (mM): NaCl 144, KCl 5.9, MgCl2 1.2, CaC12 2.5, HEPES 10 and glucose 11.…”

Section: Methodsmentioning

confidence: 99%

(+)‐Isradipine but not (−)‐Bay‐K‐8644 exhibits voltage‐dependent effects on cat adrenal catecholamine release

López

Michelena

Gandı́a

et al. 1991

1 Catecholamine release from cat adrenal glands perfused at a high rate (4mlmin-1) at 37°C with polarizing (1.2 or 5.9 mm K+) or depolarizing (17.7, 35, 59 6 Potentiation of secretion by (-)-Bay K 8644 was concentration-dependent from 10-8 to 10-6 M. At 10-5M, such potentiation largely disappeared in both polarized and depolarized glands. However, this dual effect of (-)Bay K 8644 was better seen in depolarizing conditions, suggesting that using the same enantiomer, the voltage-dependence is only seen when blockade of secretion dominates. 7 In the presence of increasing concentrations of (-)Bay K 8644 (3 x 10-9, 3 x 10-8 and 3 x 10-7M), the concentration-response curves for (+)isradipine to inhibit secretion were displaced to the right. However, a Schild plot of (dose ratio -1) against (-)-Bay K 8644 concentrations gave a slope of 0.6, suggesting that the interactions between (+)-isradipine and (-)Bay K 8644 were non-competitive in nature. The pA2 for (-)-Bay K 8644 was 9.13. 8 Overall, the results suggest that potentiation of secretion by (-)Bay K 8644 (a voltage-independent phenomenon), and blockade by (+)-isradipine or (+-Bay K 8644 (a voltage-dependent phenomenon) might be exerted through binding of the dihydropyridines activators and blockers to separate sites on chromaffin cell L-type Ca2 + channels.