Effects of histamine on the contractile and electrical activity in isolated lymphatic vessels of the guinea-pig mesentery

Abstract

1 The effect of histamine on the rate of lymphatic vessel constrictions and lymphatic smooth muscle membrane potential was examined in the guinea-pig mesentery. 2 Histamine (0.01-5 micro M) increased the frequency and decreased the amplitude of constrictions in lymphatic vessels under intraluminal perfusion. This response was accompanied by a depolarization of the smooth muscle membrane potential, an increase in the activity of spontaneous transient depolarizations (STDs), the proposed pacemaker for constrictions in these vessels, and an increase in the occurrence of action potentials. 3 Responses to histamine were inhibited by the H(1) receptor antagonist pyrilamine (0.2 micro M), but unaffected by NO synthase inhibition with N(G)-nitro L-arginine (L-NOARG, 100 micro M) and lysis of the endothelium. 4 In about 50% of the vessels, a decrease in constriction frequency, STD activity and a smooth muscle hyperpolarization were observed in response to dimaprit (10 micro M), suggesting the presence of H(2) receptors. These vessels had also a significantly lower basal contractile rate. Lymphatic vessel pumping was not affected by R-alpha-methylhistamine (10-50 micro M), ruling out a role for H(3) receptor stimulation in the histamine response. 5 The present results suggest a direct action of histamine on the lymphatic smooth muscle via stimulation of H(1) (and in some vessels H(2)) receptors. H(1) receptors enhance and H(2) receptors slow down lymphatic pumping, the dominant effect being an increased contractile activity. Correlation of these effects with histamine-induced changes in membrane potential and STD activity suggests the involvement of these electrical changes in the initiation of the contractile response.

Figure 1

Effect of histamine on the contractile activity of lymphatic vessel of the guinea-pig mesentery. (A) Original traces of vessel diameter changes in an actively constricting lymphatic chamber where downward deflections represent constrictions. Histamine increased the frequency and decreased the amplitude of the constrictions in a concentration-dependent manner. (B) Time-course histogram showing the mean response (±s.e.m.) of seven vessels to 1 μM histamine applied for 4 min. ^*P<0.05; ^**P<0.01 vs mean of 5 min of control (paired Student's t-test).

Figure 2

Effect of the NO-synthase inhibitor L-NOARG (100 μM, (A)) and the histamine receptor antagonists pyrilamine (0.2 μM) and cimetidine (1 μM, (B)) on the concentration–response curve to histamine. The same concentration–response curve to histamine (control) was used in both graphs.

Figure 3

Effect of H₂ receptor activation in lymphatic vessels. (A) Time course histogram of the effect of dimaprit (10 μM) on the lymphatic vessel contractile activity. Half of the vessel tested responded to dimaprit with a decrease in constriction rate (closed columns), whereas the other half did not respond at all (open columns). ^*P<0.05 vs mean of 5 min of control (paired Student's t-test). (B) Concentration–response curves to histamine in vessels that responded to dimaprit and in vessels that did not respond to dimaprit. These latter showed a higher basal rate (closed column in right inset panel) and a flatter slope to reach a maximal response similar to that of the vessels responding to dimaprit.

Figure 4

Effects of histamine on membrane potential and action potential and STD activity in guinea-pig mesenteric lymphatic smooth muscle. (A) Intracellular microelectrode recordings from two different preparations in response to 0.1 μM (a) and 0.5 μM histamine (b) applied for 1 min (horizontal bars). Histamine caused a depolarization and an increase in the occurrence of action potentials. These events were observed to be coupled to vessel constrictions that led in one case (b) in the lost of the impalement. (B) In the presence of nifedipine to block action potentials, application of the same concentrations of histamine to two other vessels caused a depolarization and an increase in the frequency and amplitude of STDs (upward deflections). (C) STD frequency and amplitude measured during the maximum response to histamine (0.1 μM, a) and (0.5 μM, b) expressed as a percentage of the values obtained during the same impalement, before histamine application. Column values are means±s.e.m. of eight (a) and 13 experiments (b), some of which were carried out in the presence of nifedipine. Resting membrane potential values in this and subsequent figures are indicated on the left side of the traces.

Figure 5

Effect of pyrilamine on the membrane potential response to histamine. The marked depolarization caused by a 1-min application of 0.5 μM histamine (horizontal bar, (A)) was completely abolished while the preparation was superfused with 0.2 μM pyrilamine. (B) Scale bars apply to both recordings, obtained from the same impalement. Nifedipine (2 μM) was present throughout the experiment to avoid histamine-induced action potential-associated constrictions.

Figure 6

Effect of dimaprit on the membrane potential of lymphatic smooth muscle. (A) Dimaprit (10 μM) applied for 1 min (horizontal bar) induced a hyperpolarization and a decrease in STD activity in about 50% of the vessel tested. (B) Histograms of STD frequency and amplitude measured during the maximum response to dimaprit in the responding preparations, expressed as a percentage of the values obtained during the same impalement, before dimaprit application. Column values are means±s.e.mean of four experiments. ^*P<0.02 vs control (paired Student's t-test).