Heterogeneity of calcium channels in mast cells and basophils and the possible relevance to pathophysiology of lung diseases: a review

Protective effect of T-type calcium channel blocker in histamine-induced paw inflammation in rat

The aim of this paper was to investigate the protective effect of the T-type calcium channel blocker in a model of acute local inflammation (histamine-induced). The intraplantar injection of histamine elicited an inflammatory response that was characterized by a time-dependent increase in paw oedema and neutrophil infiltration in paw tissue. The maximal increase in paw volume was observed at 90 min after histamine administration (maximal paw volume: 0.97 +/- 0.07). In addition, polymorphonuclear leucocyte (PNL) number was markedly increased in the histamine-treated paw tissue (144 +/- 25.56). However, histamine-induced paw oedema was significantly reduced in a dose-dependent manner by treatment with mibefradil (given at 10, 25, 50, and 100 mg x kg(-1)) at 30, 60, 90, 120, 150, 180 min after injection of histamine. Mibefradil treatment also caused a significant reduction of the polymorphonuclear leucocyte number in the paw tissue. Our findings support the view that mibefradil exerts antiinflammatory effects.

Inhibition of voltage-dependent Ca2+ channels of porcine tracheal smooth muscle by the novel Ca2+ channel antagonist RWJ-22108

1. We compared electrophysiological effects of the bronchoselective Ca2+ channel antagonist RWJ-22108 on voltage-dependent Ca2+ channels (VDCs) of porcine tracheal smooth muscle cells to the effects of nicardipine and verapamil. 2. Each of the three Ca2+ channel antagonists tested inhibited inward Ca2+ currents (ICa) measured by whole-cell patch clamp techniques. Inhibition was dose-dependent with approximately 50% inhibition of peak ICa at +20 mV obtained with 3 x 10(-6) M RWJ-22108, 3 x 10(-7) M nicardipine, or 10(-5) M verapamil. 3. Both RWJ-22108 (3 x 10(-6) M) and nicardipine (3 x 10(-7) M) shifted the voltage dependence of steady-state inactivation to more negative potentials; however, the change in the potential of half-maximal inactivation induced by RWJ-22108 (-18 mV) was significantly greater than that induced by nicardipine (-12 mV). Verapamil did not alter the voltage dependence of inactivation. 4. We conclude that inhibition of VDCs by RWJ-22108 is qualitatively similar to that by nicardipine but with a greater stabilizing effect on the inactivated channel state.

The human inflammatory response

Inflammation is a protective response of vascularized tissue normally elicited toward nonself-determinants or tissue injury. Inflammation functions as part of normal host surveillance mechanisms to destroy or quarantine both harmful agents and damaged tissue. Most forms of inflammation are exaggerated out of proportion to the stimulus, because humoral amplification systems recruit additional components of the immune system initiating the production of proinflammatory mediators, including cytokines synthesized by activated macrophages. These act as secondary messengers to induce synthesis and expression of specific adhesion molecules on endothelial cells and white cells. Polymorphonuclear leukocytes play a central role in the acute inflammatory response. Anaphylaxis, an immediate hypersensitivity reaction to substances administered in the perioperative period, serves as a useful model for some of the problems of acute inflammation because there are important interrelationships with the cardiovascular system, endothelium, and coagulation. Mast cells and basophils produce the acute inflammation associated with anaphylaxis mediated by immunoglobulin E (IgE) antibodies, whereas the immunoglobulin G (IgG)-antigen interaction activates the complement cascade to generate anaphylatoxins, specifically C5a. Activation of white cells causes release of proteolytic enzymes, production of oxygen-derived free radicals, and the synthesis of a variety of lipid mediators. Protamine sulfate is one of the most common causes of life-threatening anaphylactic reactions during cardiac surgery. Differing responses occur, dependent on the presence of either IgE or IgG antibodies with the activation of the mast cell or the complement system, respectively. The many different amplifying pathways that can be recruited during anaphylaxis and the array of mediators involved are important when therapeutic intervention is considered. The challenge for the future will be to identify a pharmacologic agent that will arrest the inflammatory cascade and thus prevent further amplification and resultant host injury.

The ideal agent for perioperative hypertension and potential cytoprotective effects

Perioperative hypertension is primarily due to increased systemic vascular resistance (SVR). Therefore, the major therapeutic approaches are directed at reducing vasoconstriction, using drugs that increase cyclic nucleotides or block calcium entry into vascular smooth muscle. Nitroprusside and other nitric oxide-derived vasodilators affect both the resistance vessels and the vascular capacitance bed. Antihypertensive drugs that affect venous return can have unpredictable effects on blood pressure and calculated SVR. The new intravenous dihydropyridine calcium antagonists have arterial vasodilating actions and are especially promising as new therapeutic approaches for perioperative hypertension. Following coronary bypass-grafting, patients have undergone direct mechanical manipulation of their native grafts, coronary arteries, and internal mammary artery, creating a potential risk for coronary or internal mammary spasm. Calcium antagonists may be an important therapy for perioperative hypertension in such patients. Experimental models have demonstrated that calcium antagonists can attenuate the production of inflammatory mediators and thereby reduce cellular damage following reperfusion. These potential anti-inflammatory drugs may prove to offer additional benefits in the therapy of perioperative hypertension. The potential anti-inflammatory and cytoprotective effects of calcium antagonists may make them the ideal agents for the treatment of acute perioperative hypertension.

RWJ-22108--a novel airway tissue--selective calcium channel blocker

RWJ-22108 is a novel calcium entry blocker that has potential therapeutic use as an antiasthmatic agent. Although displaying typical potent inhibition of 45Ca uptake into aortic rings (IC50 = 7.1 nM) and displacement of [3H]nitrendipine from cardiac membranes (IC50 = 137 nM), RWJ-22108 demonstrates tissue selectivity in the inhibition of KCl-induced contractions. RWJ-22108 inhibits the calcium-dependent contraction of canine bronchiolar smooth muscle with an IC50 of 5.7 nM. The IC50 femoral artery/IC50 bronchiolar ratios are 2.85, 8.02, 1.47 and 1.96 for nifedipine, RWJ-22108, verapamil, and gallopamil, respectively. Furthermore, this selectivity ratio (range 2.8-5.5) of RWJ-22108 is also observed when inhibition of other pulmonary and cardiovascular smooth muscles are compared. Using canine tracheal muscle and rabbit aortae, the IC50 aorta/IC50 trachea ratio is 1.75 for RWJ-22108 compared to approximately 0.5 for several calcium blocker standards. These results indicate that in vitro RWJ-22108 is a bronchoselective calcium channel blocker.

Divalent cation dependence of the inhibition by phenothiazines of mediator release from mast cells

1. The divalent cations calcium, strontium and barium--and in that order of decreasing effectiveness--were capable of supporting the stimulated release of histamine from rat peritoneal mast cells (RPMC). 2. The responsiveness of mast cells to stimulation in the presence of divalent cations was, in general, markedly enhanced when the cells were first depleted of their intracellular calcium stores. 3. The putative calmodulin antagonists, chlorpromazine, promethazine, thioridazine (phenothiazines) and W-7 (a naphthalene sulphonamide) all inhibited histamine release in the presence of divalent cations in both untreated cells and in RPMC depleted of their intracellular calcium. 4. Histamine release induced by antigen, compound 48/80 and ionophore A23187 was inhibited by this class of compounds most effectively in the presence of extracellular barium, less so in the presence of strontium and least so in calcium-containing media. 5. In the experimental situation where the extracellular calcium concentration was reduced (less than 1 mM), the phenothiazines inhibited the stimulated release of histamine more effectively. 6. In toto, these results suggest that strontium and barium, as well as calcium, can support histamine release from RPMC by directly interacting with an intracellular divalent cation-binding site that may be calmodulin. As a consequence, one mechanism by which the phenothiazines and W-7 may modulate the secretory response could reflect an antagonism of a divalent cation interaction at that same site, although other additional potential sites of inhibitory action are indicated, dependent on the stimulus employed for secretion.

Dual effect of dihydropyridines on 45Ca uptake induced by the K+ -channel blocker, 4-aminopyridin on mast cells

The 1,4-dihydropyridines (DHP) are calcium antagonists and represent a new class of drugs which act by a selective inhibition of Ca++ influx through voltage-operated calcium channels. We report the effect of nifedipine (Bay A 1040), nisoldipine (Bay K 5552) and nitrendipine (Bay E 5009) on the histamine release and on the 45Ca uptake promoted by 4-aminopyridin in mast cells. These cells treated with DHP (10(-12)-10(-3) M) activated the secretory response in a dose-dependent manner in the range of concentrations 10(-6)-10(-3) M, whereas concentrations of 10(-12)-10(-6) M did not significantly inhibit the secretion. 4-Aminopyridin, a known K+ -channel blocker, induced 45Ca uptake. Pretreatment of mast cells with DHP prior to 4-aminopyridin stimulation inhibited or stimulated 45Ca uptake depending on concentration; thus, concentrations of DHP below 10(-12) of nitrendipine and 10(-9) for nisoldipine and nifedipine were inhibitory, while higher doses potentiated 45Ca uptake. These results demonstrate a diversity of pharmacological effects of DHP on mediator secretion and 45Ca uptake in mast cells and throw into question their only properties as Ca++ antagonists.

The obligatory role of calcium in the development of antigen-induced airway hyperreactivity to cold provocation in the rat isolated trachea

The effect of antigen challenge on cold provocation (30-10 degrees C) in isolated tracheal segments from control (normal) and ovalbumin-sensitized rats was studied. Sensitization alone or acute cold provocation (10 degrees C) alone was not sufficient to cause contraction of tracheal smooth muscle preparation. Following recovery from antigen-induced responses (Schultz-Dale phenomenon) in sensitized rat segments, cold provocation induced strong contractile responses. Both the antigen-induced contractions and the subsequent development of airway hyperreactivity to cold were dependent on extracellular Ca2+ and inhibited by verapamil. The data in this study indicate that extracellular Ca2+ plays an obligatory role in the mediation of antigen-induced contractile responses as well as the subsequent development of hyperreactivity to cold provocation in rat tracheal smooth muscle.