Beta‐adrenergic inhibition of bovine mesenteric lymphatics.

Abstract

SUMMARY1. The f-action of catecholamines on lymphatic smooth muscle was studied by observing the effect of isoprenaline on electrical and mechanical activity in the double sucrose-gap.2. Action potentials and phasic contractions evoked by depolarizing pulses were abolished within 2 min of drug addition.3. Isoprenaline hyperpolarized the membrane and increased membrane conductance.4. Tetraethylammonium (10 mM) did not itself affect membrane resistance but reduced the hyperpolarization and the increase in conductance caused by isoprenaline.5. Removal of K+ from the external solution reduced membrane conductance and increased the hyperpolarization due to isoprenaline.6. When the NaCl content of Krebs solution was replaced with LiCl or choline chloride, isoprenaline no longer blocked action potential firing and its effects on phasic contractions and membrane conductance were reduced.7. In contrast, ouabain (10-5 M) did not block the effect of isoprenaline on membrane potential and membrane conductance.8. These results suggest that fl-adrenergic inhibition of lymphatic smooth muscle involves an increase in an outward K+ current, though an additional metabolic effect cannot be ruled out.

Transient Excitatory Responses to Sustained Stimulation of Intramural Nerves in Isolated Bovine Lymphatic Vessels

“…Thus the complex inotropic response to field stimulation observed in the present study (which could either be positive or negative, biphasic of triphasic) cannot be attributed to the actions of another transmitter. We do know, however, that noradrenaline can have both positive and negative inotropic effects on lymphatic smooth muscle depending on whether the ax-or fl-effect predominates (Allen, Iggulden & McHale, 1986) or because of an inverse relationship between force and frequency of contraction shown by McHale & Roddie (1983) and evident in the response to 18 mM-K' in Fig. 4 of the present study.…”

Outward Currents in Smooth Muscle Cells Isolated from Sheep Mesenteric Lymphatics

“…It is possible that both the voltage-dependent current and the BK current could play a part in repolarizing lymphatic action potentials. In double sucrose gap studies on bovine mesenteric lymphatics, 10 mÒ TEA increased the amplitude and duration of the evoked action potential (Allen, Iggulden & McHale, 1986;Allen & McHale, 1988). Since TEA is a potent blocker of BK channels (see Carl et al 1996) as well as the voltagedependent K¤ current, its effect on the action potential is difficult to interpret.…”

ATP‐sensitive K+ channels in smooth muscle cells of guinea‐pig mesenteric lymphatics: role in nitric oxide and β‐adrenoceptor agonist‐induced hyperpolarizations

“…Lymphatic pumping can be signi®cantly aected by various factors, which in¯uence the rhythm and amplitude of these spontaneous constrictions. Substances like nitric oxide (NO), released by the endothelium which separates the smooth muscle from the vessel lumen, or the badrenoceptor agonist, isoprenaline, have been shown to decrease the frequency of the spontaneous constrictions and to hyperpolarize membrane potential of the lymphatic smooth muscle via the activation of K + conductances (Allen et al, 1986;. Hyperpolarizations evoked by NO and isoprenaline were shown to be mediated by an increase in the intracellular concentration of cyclic monophosphate nucleotides.…”