Modification of potassium‐evoked release of noradrenaline by various ions and agents

Abstract

(1968) showed that high K+ evokes secretion of noradrenaline (NA) from the sympathetic nerves of the cat spleen in a calciumdependent manner. It has also been reported that agents which increase the duration of the action potential, such as tetraethylammonium (TEA) and 4-aminopyridine (4-AP), markedly potentiate the release evoked by nerve stimulation (Thoenen, Haefely & Staehelin, 1967;Gillespie & Tilmisany, 1976;Wakade, 1980) Wakade (1981aWakade ( , 1982 further extended these observations in the guinea-pig heart, showing that TEA (20 mM) enhanced the response to 35 and 70 mM K+ i) The Macmillan Press Ltd 1983 278 S.M. KIRPEKAR, J.C. PRAT & M.T. SCHIAVONE by 5 fold and 1.5 fold, respectively, and that TTX blocked this potentiation. They suggested that a part of the release induced by high K+ is due to regenerative activity, since the response was partially blocked by TTX and potentiated by TEA.The primary purpose of this study was to reassess the secretory response to excess K+ in the cat spleen. Our previous investigations of K+-evoked NA release in the cat spleen focused on responses to very high K+ concentrations (bolus injection of 3.7 M K+ or prolonged application of 140 mM K+) (Kirpekar & Wakade, 1968;Kirpekar et al., 1976; Kirpekar etal., 1977;Garcia, Kirpekar & Pascual, 1978). In the present study, we have used intermediate concentrations of K+ to re-examine the role of regenerative depolarization in K+-evoked secretion and the mechanisms of muscarinic inhibition and aautoinhibition in the splenic nerve terminals. Methods Spleen slicesCats were anaesthetized with ether. The abdomen was opened by a midline incision, then the spleen was quickly removed and cut into transverse sections (0.5 to 0.7 mm thick), using a tissue slicer. To label the NA stores of the splenic nerve, the slices were incubated for 30 min with 10 ml of Krebs solution containing 10 pCi of (±)-[3H]-NA (specific activity 7.5 Ci/mmol), then washed 3 times in 20 ml of Krebs solution over a 30 min period. In each experiment, a number of slices (approximately 100 mg) were incubated in 10 ml of Krebs solution for 5 min to determine the background release, then transferred to 10 ml of a test solution for 5 min. The incubation temperature was 37°C. Perfused adrenal glandLeft and right adrenal glands were prepared for retrograde perfusion at room temperature according to the procedure of Garcia, Hernandez, Horga & Sanchez-Garcia (1980). The perfusion rate was about 1 ml/min. Glands were perfused for about 30 min before the start of each experiment. Perfusion and incubation solutionsKrebs bicarbonate buffer consisted of (mM): NaCl 118, KCl 4.7, CaCl2 2.5, MgSO4-7H2O 1.2, KH2PO4 1.2, NaHCO3 25, and glucose 10. When excess K+ (as K2SO4) was added, an osmotic equivalent of NaCl was concomitantly removed. For studies with La3", 2+or 10mMNa, a Tris-buffered solution was used, consisting of (mM): NaCl 143, KCl 6.7, CaC12 2.5, MgSO4-7H20, 2.4, Tris (hydroxymethyl)-aminomethane (Tris) 5.0, and glucose 10. When NaCl was decreased to 10 mM, 266 mM su...

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

“…Enhanced transmitter release has a common underlying mechanism bothfor tetraethylammonium and 4-aminopyridine TEA had been shown previously to enhance the spontaneous release of catecholamines from perfused guinea-pig heart (Wakade & Wakade, 1981), cat splenic slices and perfused adrenal gland (Kirpekar et al, 1983). Here, we have demonstrated a similar effect for 4-AP, guanidine being a much weaker secretagogue.…”

“…In a recent paper (Kirpekar et al, 1983) we observed that La3+ and Mn+ inhibited the release of tritium evoked by TEA; however, in the s present paper high Mg2" did not affect the secretory responses to TEA or 4-AP (Figure 4). This was a paradoxical finding since it is well known that Mg2", f La3+ and Mn2" behave as inorganic Ca2" antagonists I that inhibit equally noradrenaline release evoked by depolarizing stimuli (Kirpekar & Misu, 1967;Kirpekar & Wakade, 1968;Kirpekar et al, 1972).…”

“…Depolarization is likely to be involved in the secretory response Because TEA and 4-AP, by specifically blocking K' conductance, cause depolarization in a variety of cell: (Bowman & Savage, 1981), it is reasonable to assume that such a depolarizing effect might be implicated ir the secretory effects of the drugs (Kirpekar et al 1983). On the other hand, if depolarization of sym pathetic nerve terminals were the unique mechanisn involved, the releasing effects ofTEA and 4-AP shoulc mimic the secretory response obtained by other de polarizing stimuli such as high K+ or veratridine.…”

The Effect of Barium on [3H]Noradrenalin Release from the Human Neuroblastoma SH‐SY5Y

“…This in turn would open voltage-sensitive Ca2+ channels, enabling Ba2+ to enter the cell. Additional support for this hypothesis is provided by the observation that tetraethyl ammonium (a potassium channel blocker) stimulates catecholamine release from sympathetic neurons (Kirpekar et al, 1983) and chromaffin cells (Sorimachi et al, 1990) and prolactin secretion from GH4Cl cells (Wang eral., 1991). Studies with digitoninpermeabilized chromaffin cells (Izumi et al, 1986;TerBush and Holz, 1992) suggest that Ba2+ has a direct effect on exocytosis rather than stimulating catecholamine release indirectly via release of Ca2+ from internal stores.…”

Ca(2+)‐activated K+ channels modulate muscarinic secretion in cat chromaffin cells.

“…After an initial secretary peak (around 2000 ng 30 s-1) the rate of catecholamine release declined to a plateau at around 700 ng 30 s-5. Stimulation by TEA of catecholamine release from perfused cat adrenals was previously reported by Kirpekar, Prat & Schiavone (1983); they attributed this effect to depolarization by TEA of chromaffin cells which, as demonstrated later on, caused marked fluctuations in cytosolic Ca2+ concentrations (Sorimachi, Yamagami & Nishimura, 1990). (Fig.…”